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Acanthostega (autapomorphies)

Answer 1

Acanthostega has the following autapomorphies: Two temporal emarginations (otic notches); one between the temporal and the squamosal (as in several other tetrapods) and one completely enclosed by the tabular. This is not known in any other tetrapod. Loss of the intertemporal (like Ichthyostega

Answer 2

• By end of Devonian CO2 had declined to 2000 ppm, about 5X our present-day levels. • Levels continued to drop and by the middle of the Carboniferous, CO2 concentrations had dropped to around 400 ppm or essentially Ice Age in a Tropical World! • The Carboniferous is generally thought of as a hot, humid period, but the fossil and geological evidence also point to another climate trend *Iwo Ice-ace ouisesi • The first in the Mississppian between 359 and 318 mlye • The second and more significant of the two occurred in the Pennsylvanian between 318 and 299 mya. Continents & Climate • Pangea was a super continent of that time period and much of its land mass occupied the southern memsonere • Does a single land mass such as this contribute to harsher climates? • What evidence do we have? • Only the near equatorial placement of the Euramerican portion of Pangea permitted terrestrial laund and told to survive trouen te second and more severe Ice hee or th rennsvivanar • Oceanic lite was less adverselv attected than terrestriall • Mean global temperatures ranged from 20'C throughout the Mississippian but plunged in the Pennsvivanian to between 12 Cand 1e • Our present-day global average is approximately 16°C Pennsylvanian experienced a great deal of continental movement resulting in increased elevation over much of the earth’s surface. • Increased elevation contributed to cooling trend. • Cooler environments contributed to the appearance of conifers and likely also to the appearance of amniotes. Why? • Cooling is also evident in the pronounced decline of lycopods, a terrestrial primitive plant that had been common in the Mississippian As plants died during the Mississippian, and to a lesser degree the Pennsylvanian, and were buried, decomposition was slow and the continued burial of plants resulted in the coal formation that this period is famous, and which fueled our industrial revolution two centuries ago.

Answer 3

Jaw wless forms were gone except for the fossil remains of conodonts. • The relatives of modern lampreys and hagfish were undoubtedly around but the fossil record is generally silent on this. • Jawed fish continued to diversify • Acanthodians (spiny sharks) were a major constituent of the fauna • Sharks were more diverse and produced some rather interesting forms • Among actinopterygians, the more advanced Neopterygii make their appearance. • Sarcopterygians remain, but it is their descendants, the tetrapods, that are most

Answer 4

Sharks • Dominated the marine environments of the Carboniferous • Two forms were particularly plentiful: xenacanthids, and stethacantids. • Xenacanthids were about 1 metre in length and were unusual in having two divergent cusps on their teeth. • Stethacanthids were more curious with some species being sexually dimorphic (top right)

Answer 5

Actinopterygi- dermal bones with ganoin, rhomboidal scales w/ peg-and-socket articulation. Actinopteri- branching rays in all fins. NODE A: Supraorbital bones present. NODE B: Antorbital bones present. Tooth-bearing elements -Lepidotrichia covering actinotrichia -ganoid scales

Answer 6

Advanced feeding • maxilla not contacting palatoquadrate, maxilla mobile, symplectic present, clavicle lost. • Quadrate separate from palatoquadrate In Amia (a neopterygian), there are new elements in the jaw – the symplectic and supramaxilla. The maxilla is hinged not fixed to the skull and, therefore, is able to rotate about a hinge at the front of the jaw. The maxilla can also bow out increasing the size of the buccal cavity

Answer 7

Reduce maxilla, increase premaxilla -New elements, reduce other elements -Change shape of skull, therefore of mouth -Reduce length of Hyomandibula, with new element-Symplectic -Braincase fusion -Coronoid process of dentary -Lateral Line System in grooves rather than in canals -Scales lose dentine-like layer, then ganoine, reduce articulation btw sinking of scales beneath skin, and associate some with centra -Dermal skull elements also sink beneath skin after loss of ganoine layer-musculature can attach to outside of bone surfaces -Ossification of centra-solid unperforated centra- compact -Development of compact caudal skeleton -Heteroceral-abbreviated heterocercal-homocercal caudal fin, associated with changes in paired fins

Answer 8

They share the following derived characters: • Large interpterygoid vacuities (open palate). These may have been used in breathing as part of a buccal pump (as in frogs). • Occipital condyles present, notochord excluded from skull. • The skull table is firmly sutured with the cheek. There was no mobility between the two units. There are only four digits in hand. Temnospondyl skull anatomy Note the very large openings in the palate of the temnospondyl, Dendrerpeton. These large vacuities may have been important in temnospondyl respiration.

Answer 9

Lepospondyls appear in the Mississippian. They are united by a few synapomorphies: They are all relatively small. They all lack an otic notch. Lack labyrinthine infolding in the teeth The centrum of lepospondyls is large and cylindrical. Usually have a single central element (at least in the presacral series), although recently quite a few taxa have been discovered Very long bodies – aïstopods often have over 200 vertebrae. • All lepospondyls have a single vertebral centrum. In aïstopods the neural arch is fused to the centrum. • All aïstopods lack limbs and appear to have been semi- aquatic. • Some nectrideans were long-bodied, but it was the tail that was long, and all had limbs. However, the limbs were poorly ossified suggesting that they were primarily aquatic. Long-bodied lepospondyls (Aïstopoda & Nectridea) Microsaurs (The reptile- like lepospondyls)

Answer 10

major groups of lepospondyls: Aïstopoda, Nectridea, Microsauria, and Lysorophidae. Together, lepospondyls have been regarded as sister-taxon to Amniota, as sister-taxon to Lissamphibia, or as sister-taxon to Caecilia, which would render Lissamphibia paraphyletic Three key characters in the debate: • 1) Pedicellate teeth. In teeth of this type, the crown is separated from the root (pedicel) by a zone of fibrous tissue. • 2) Cylindrical centra. This applies to taxa in which the vertebrae each have a single, cylinder-shaped centrum, rather than a separate pleurocentrum and intercentrum. • 3) Bicuspid teeth. A bicuspid tooth, which may also be pedicellate, is one that bears two distinct prominences (cusps)

Answer 11

Amniota Oldest fossil eggs: Early Jurassic (194 Ma) Oldest fossil amniotes: Pennsylvanian (316 Mya) - Provide stable environment for development, protected from d Must rely on skeletal features to identify fossil amniotes → two proximal tarsals (ankle bones: astragalus and calcaneum) ?Braincase anatomy Amniotic egg → amniotes  Extraembryonic membranes (amnion, chorion, allantois, yolk sac) → develop from the embryo

Answer 12

Seymouria (another stem amniote) shares the following derived characters with amniotes: Cheek strongly sutured to skull table. No lateral-line canal grooves. A transverse flange of the pterygoid (although it doesn’t have a row of large teeth). Small, crescentic intercentra and large, cylindrical pleurocentra.

Answer 13

Reptiliomorpha Paraphyletic assemblage: containing reptile-like Palaeozoic amphibians alongside the most basal members of two amniote clades that still exist today – Diapsida and Synapsid

Answer 14

Axial skeleton: A proper atlas and axis complex is present. This includes the presence of a proatlas. Appendicular skeleton: Astragalus formed from 3 ossifications.

Answer 15

• Note the exceptionally large rostral portion of the skull (i.e. the part anterior to the orbit) and the recurved teeth. • This taxon had an immense head relative to the size of its body, and appears to have been an ambush predator that lived along the banks of rivers or other bodies of fresh water, playing an ecological role similar to that of modern day crocodiles

Answer 16

Pangeawas the major land mass • Twosmaller land masses corresponding to Asia (China and Siberia) extended out to the east.There were also a number of smaller islands. • ThePalaeo-Tethys Ocean and the much larger PanthalassicOceanwere the two main bodies of water the end-Carboniferous Ice Ageand the decline in CO2 that had taken place during that time, warming continued into the Permian • TheExtensive forest fires of the Carboniferous had returned a great deal of CO2 back into the atmosphere. • With increasing CO2,oxygen rates, which had reached exceptionally high levels during the Carboniferous started to drop. • You may consider: 1) the consequences; 2) relevance of hydrogen sulfide production on atmospheric oxygen and ozone • LatePermian volcanic activity hasbeen linked to the end-Permian extinction event. Large bodies of rock known asbasalt traps, occurring in what is now Siberia Jawless fish are only known from fragments – notably the conodont teeth. • Jawed fish fared a little better. • Sharks appear to have been hit hard by the extreme weather of the Permian and few fossils are known. • Bony fish also remain diverse and two distinct groups can be found: the Teleostei and the paraphyletic Holostei.

Answer 17

Temnospondyls • Permian diversification • Diverse group • Larval stages and metamorphosis • Broad, ornamented skulls with rounded snouts • Includes ancestors of modern amphibians? Temnospondyli are diverse and dominate the semiaquatic habitats of the period. • Somesuch asCacops(top) were fully terrestrial and about 40 to 50 cm in length

Answer 18

Lepospondyls • Early Permian • Incredibly diverse group; some forms limbless • Larval stages and metamorphosis Diplocaulid Nectrideans lown from the Lower Pennsylvanian through the Lower Permian, this taxon represents uatic group of lepospondy • Unlike Aïstopods, nectrideans retained their limbs. • Most nectrideans have a flat, wide, short skull shaped like a boomerang. i the tabular and squamosal are very large and project posterolateraly into a tabular • There is no intertemporal bone on the skull table. • The basicranial articulation is fused. Like the temnospondyls the palate is open (there are large interpterygoid vacuities).

Answer 19

ʻMicrosaursʼ Themost diverse and successful of the lepospondyls. They range from the Mississippian to the Lower Permian. Like the temnospondyls discussed earlier, the “microsaurs” may be the only Paleozoic amphibians to have living descendants! synapomorphies? No intertemporal. No supratemporal. Possess abroad occipital condyle (depression) articulating against the atlantal condyle. NOTE:This is the opposite condition of what is

Answer 20

Stem Amniotes Diadectomorphs (Limnoscelis, Diadectes) • Early Permian (a few basal members in latest Pennsylvanian) • Most amniote-like “amphibians” ➔ similarities in skulls and ankles • Large animals, more erect postures ➔ increased terrestriality in some forms • Includes first terrestrial herbivores • Loss of labyrinthine infolding on teeth • Why do we consider these to be stem amniotes? Diadectes The first herbivorous terrestrial vertebrate. 1 Tricuspid cheek teeth with large central cusp bounded lingually and labially by additional cusps. 2 Spatulate incisors capable of stripping plant material from stems. 3 Expanded cheek teeth (molariform dentition). 4 Jawarticulation below level of dental occlusal surface. 5 Depth of skull exceeds 50%of skull length. 6 Depth of lower jaw at coronoid eminence exceeds33%of lower jaw length.

Answer 21

Exoccipital united with occipital flange of occipital margin of skull table. 2- Supraoccipital exposed occipitally, forming medial portion of dorsal margin of occipital. plate above foramen magnum. 3- Posttemporal fenestra located on verroidicidi oruer or oculout teriesue bounded dorsally by occipital flanges of postparietal and tabular, and dorsal portion o lateral margin of supraoccipital-opisthotic complex, tenestra bounded ventrally by laterally directed paroccipital process. 4- Paroccipital present but ventrolaterally oriented. 5- Occipital and opisthotic flanges of tabular exoanoeo ano ventromed aliv tuseo laterai margin of supraoccipital.

Answer 22

Phylogenetic studies of pelycosaurs have proposed that within this group six major clades (families) can be recognized: Eothyrididae (small insectivores) Caseidae and Edaphosauridae (two different types of large, bulky herbivores) Varanopseidae, Ophiacodontidae and Sphenacodontidae (three different types of medium to large-sized carnivores)

Answer 23

Asprimitive synapsids, pelycosaurs are diagnosed by the presence of synapomorphies that distinguish them from other Paleozoic tetrapods: • lateral temporal fenestra bordered by jugal, squamosal and postorbital bones • anteriorly inclined plate-like occiput • small posttemporal fenestra bordered by the supraoccipital, tabular, and opisthotic bones • pillar-like septomaxilla has a broad base that straddles the maxilla-premaxillary suture. Pelycosaurs retain anumber of features that appearin the derived condition in all other amniotes, including therapsids. These features include: • presence of broad, plate-like supratemporals (small & slender in Varanosaurus) on the dorsal surface of the skull • large tabulars (circled on figure) • two coronoids on the lower jaw • and amedial centrale in the pes

Answer 24

s family was erected asa provisional group by Romer and Price (1940) for the small pelycosaurEothyris, known from a single skull from the Lower Permian of Texas,and fragmentary remains of three large pelycosaurs Wedge-like dorsal process of premaxilla forms an anteriorly pointed rostrum. External narial shelf, formed by each nasal, located beneath the dorsal margin of the narial openings. The external nares are anteroposteriorly elongate, occupying at leastone- fifteenth of the skull length, or 25%of snout length. The external surface of each maxilla faces ventrolaterally rather than being oriented vertically. Marginal dentition reduced to 22 teeth or fewer. Antorbital width of the skull is greatest across the lacrimals. Parietal foramen unusually large, equal or larger in diameter than the foramen magnum. Quadratojugal elongate, extending far anteriorly under the temporal fenestra. Br oa d lateral wing of exoccipital

Answer 25

Caseid post-cranial anatomy Reduction in the phalangeal formula, ranging from 2-3-4-4-3 to 2-2-2-3-2. T w o distinct types of terminal phalanges can be found in caseids. I n Cotylorhynchus (shown here) the claw bearing element is very large and broad, with apparently sharp edges on the sides.

Answer 26

Eupelycosauria Aclade that includes all synapsids except eothyridids and caseids. Eupelycosaurs are characterized by: Reduction in the width of the snout Redictopm in the width supratemporal (blue) Increased contribution of the frontal (green) to the dorsal orbital margin Location of the pineal foramen along the interparietal suture Reduced length of the skull table and in the length of the parietal (beige)relative to the length of the frontal. Archaeothyris (Late Carboniferous) & Ophiacodon (Early Permian) • Pelycosaurs have been distinguished from other synapsids mainly on geological and geographical grounds. • Although easily recognizable, and readily separated from more advanced synapsids, pelycosaurs represent a paraphyletic grade of basal synapsids that includes the ancestors of advanced synapsids (therapsids and mammals).

Answer 27

Sphenacodontids and the origin of therapsids Sphenacodonts have a supracanine buttress of the medial surface of the maxilla. The first premaxillary and second dentary teeth are greatly increased in size and similar in length to the enlarged canine The ventral edge of the premaxilla slopes anteroventrally, giving the snout a slightly hooked appearance. The supraorbital shelf terminates posteriorly of the concave lateral surface of the postorbital. The pineal foramen is located on a slightly raised area of the parietal, with a distinct ridge surrounding the foramen. The ventral keel of the angular is reflected slightly from the long axis of the mandible

Answer 28

Mammalian auditory ossicles: incus, malleus, stapes Ectotympanic - holds tympanic membrane. Theevolution of hearing in synapsids extended from the Carboniferous through into the Mesozoic, but it was in the Permian and Triassicwhere it really made some significant gains

Answer 29

Reptilia or Sauropsida is recognized as the clade that includes the last common ancestor of diapsids and turtles and all of their descendants KeySauropsid/Reptilia Trait • All reptiles and by extension eureptiles possess a sub-orbital foramen or as in Diapsida a fenest Petrolacosaurus vs Cotylorhynchus • The tabular bone - very reduced or lost • The supratemporal bone – dramatically reduced

Answer 30

Orovenator mayorum • Originally thought of as the earliest neodiapsid, many current phylogenies recover it as an early diverging varanopid (however, this is likely not the case) • Notice the upper temporal and suborbital fenestrae, slender triradiate jugal, slender supratemporal • There is considerable current debate that varanopids may be diapsids

Answer 31

Maiothisavros dianeae • Early Permian neodiapsid from Oklahoma, USA • Perhaps some archosauromorph affinities? • Highly autapomorphic down turned anterior tip of dentary • Large palatal dentition, especially on the transverse flange of the pterygoid • Large conical teeth, with some of the maxilla being pronounced

Answer 32

Youngina and the “Younginiformes" • Note the prototypical diapsid skull. • Given that diapsids evolved in the Carboniferous, why would their remains (fossils) be uncommon in the Permian fossil record

Answer 33

Akkedops bremneri • A South African stem saurian from the late Permian previously misidentified as Youngina and currently recovered as sister to Sauria • Several derived morphologies • Tympanic crest for tympanic membrane • Slender stapes • Lacks a lower temporal bar • Lacks tabulars and postparietals • Posteriorly emarginated quadrate • Uniquely, the supratemporal contacts the postorbitl The Foot ❑ Expanded 5th metatarsal and long ❑ Astragalus and calcaneum are unfused ❑ 5th distal tarsal present

Answer 34

Synapsida Carboniferous Synapsida (Figure 28) are represented by a number of complete specimens from North America, and particularly from Kansas and Texas. Within the Carboniferous, the record of synapsids is much more extensive and diverse than that of their diapsid cousins, and Carboniferous synapsids in fact appear to have undergone a modest adaptive radiation. Three distinct, ecologically divergent synapsid lineages appeared during the Upper Carboniferous. These respectively com- prised terrestrial predators such Haptodus and Sphenacodon, amphibious predators such as Ophiacodon (Figure 29) that occupied an ecological niche similar to that of modern crocodiles, and actual or incipient herbivores such as edaphosaurids and basal caseids. Fully herbivorous caseids seem not to have emerged until the Early Permian, but the unspecialized, non-her-bivorous basal taxon Eocasea (Figure 30) has the potential to provide insights into the evolution of herbivory.

Answer 35

Diapsids can be distinguished from all other amniotes by the presence of two openings near the back of the skull on either side (Figure 26), namely the upper temporal fenestra (UTF) and lower temporal fenestra (LTF). Anapsida (with no fenestration), Synapsida (with a lower fenestra only), and Diapsida (with both upper and lower fenestrae).

Answer 36

The amniote astragalus is a large bone in the tarsus (ankle) that contacts both the tibia and the fibula. The astragalus (Figure 24) was long thought to have been derived from the fusion of three bones that existed as separate elements in the anamniote tarsus – the tibiale, the intermedium, & the 4th (or proximal) centrale. This evolutionary hypothesis was proposed as long ago as 1941 by Bobb Schaeffer of the American Museum of Natural History. His work was later amended, but still defined the dominant view of the origin of the astragalus, namely that the three anamniote precursor bones fused into a single structure in basal amniotes such as the Permian Captorhinidae. In modern reptiles, however, developmental studies have failed to demonstrate this fusion. Instead, the astragalus forms in the embryo as an ossification originating from only two centres, usually with no contribution form the tibiale. This is exactly the condition that is found in the ontogenetic development of extant reptiles. Furthermore, the proto-astragalus present in close relatives of amniotes is structurally variable. In Proterogyrinus and Gephyrostegus, the tibiale and 4th centrale are fused to each other but not to the intermedium, whereas the microsaur Tuditanus exhibits fusion of all three elements. This almost haphazard evolutionary sequence renders the phylogenetic history of the astragalus at best equivocal.

Answer 37

Reptiliomorpha In the Carboniferous, the Reptiliomorpha represented a paraphyletic assemblage containing reptile-like Palaeozoic amphibians such as the anthracosaurs alongside the most basal members of two amniote clades that still exist today – Diapsida and Synapsida. Unfortunately, the fossil record of Reptiliomorpha in the Carboniferous is limited. For example, only one Lower Carboniferous reptile is definitively recognized, namely Hylonomus.

Answer 38

Lepospondyli & Lissamphibian Origins No discussion of the Lepospondyli would be complete without a consideration of their possible role in the origin of Lissamphibia (modern amphibians, including frogs, salamanders and caecilians). Historically, the debate over lissamphibian origins has been one of the most contentious in palaeontology, but two main hypotheses have emerged. The first is that Lissamphibia is a monophyletic group phylogenetically nested within the Temnospondyli. The second, more complex hypothesis is that Lissamphibia is polyphyletic, with anurans (frogs, including toads) and urodeles (salamanders, including newts) nested within the Temnospondyli and apodans (caecilians) nested within the Lepospondyli. Which option is preferred depends on how a number of controversial phylogenetic characters are formulated and polarized. The three characters that have been the subject of the most ardent debate are the following. Pedicellate teeth. In teeth of this type, the crown is separated from the root (pedicel) by a zone of fibrous tissue. Cylindrical centra. This applies to taxa in which the vertebrae each have a single, cylinder- shaped centrum, rather than a separate pleurocentrum and intercentrum. Bicuspid teeth. A bicuspid tooth, which may also be pedicellate, is one that bears two distinct prominences (cusps).

Answer 39

The evolution of the Impedance Matching Middle Ear (IMME) was an essential step that made it possible for terrestrial tetrapods to detect airborne sound in an effective manner. The fundamental issue is the difference in density between air and water. Sound waves propagate with much less loss of energy, and accordingly travel much farther, in water than in a less dense fluid such as air. The high density of water also permits the body of an aquatic vertebrate to receive sound through the body wall, rendering an elaborate, anatomically restricted hearing mechanism unnecessary. This is because of the similarity in density between the surrounding water and the vertebrate’s own body, resulting in a fairly seamless transition of the sound waves – the skin doesn’t act as a density interface that causes them to be reflected. Terrestrial vertebrates, by contrast, need a specialized structure capable of picking up sonic vibrations in a less conducive medium – or in other words, an ear. One of the earliest criteria for the diagnosis of Palaeozoic tetrapods was the presence or absence of paired embayments (otic notches) in the back edge of the skull. Similar embayments found in modern reptiles and amphibians accommodate external tympani (eardrums), leading palaeontologists to infer long ago that Palaeozoic taxa with otic notches must have also been endowed with tympani, and hence with an IMME. In effect, a functional IMME requires that there is a substantial difference in area between the tympanum (outer ear) and the fenestra ovalis of the inner ear. The role of a slender stapes (middle ear) is that it is able to amplify the vibrations received at the tympanum, as sound waves hit the outer tympanum. These vibrations are then transferred to the fenestra ovalis where the sound is amplified and transferred to the scala vestibuli, which is the upper part of the cochlea. Although this conclusion sounds logical, there is one very important caveat. A functional IMME requires a slender stapes that is connected to the external tympanum and capable of vibrating when airborne soundwaves impinge upon this structure. However, many Paleozoic tetrapods that possess an otic notch retain a relatively robust stapes that serves mainly as a supporting strut between the cheek and braincase, implying that an IMME could not have been present. What evidence, then, is sufficient the combination of an embayment or opening in the skull that could support an external tympanum (e.g. an otic notch), and a slender stapes that does not serve a supporting role and hence is free to transmit sound to the inner ear by vibrating.

Answer 40

\OL Members of this clade have traditionally been referred to as labyrinthodonts. Temnospondyls, as referred to in this book, also includes what were traditionally referred to as anthracosaurs. The term labyrinthodont is due to the characteristic infolding present on the tooth crowns, which consequently resemble a labyrinth when viewed in cross-section. In fact, labyrinthodont infolding is also characteristic of osteolepiform fish, as well as ichthyostegids, and was among the characters that were originally proposed to support an osteolepiform-tetrapod relationship. In any case, Temnospondyli may represent a monophyletic taxon as depicted in the cladogram presented above (Figure 14), but this is uncertain given that the exact sister-group relationships among the historically recognized temnospondyls are not fully resolved and that colosteids have often been grouped with many presently accepted members of Temnospondyli. Nevertheless, members of this possible clade can be readily recognized and include a number of very well-known taxa, which permits their morphology to be examined extensively. Among the best-known temnospondyls is Dendrerpeton. This taxon is from the Upper Pennsylvanian of Joggins, Nova Scotia, Canada and represents a small (approximately 40-50 cm long) tetrapod with a fully formed manus and pes and a complete lack of grooving on the skull, implying absence of a lateral line system. These features suggest Dendrerpeton was primarily terrestrial, in contrast to most of the Carboniferous tetrapods that we have examined thus far.

Answer 41

The key to the development of the full tetrapod limb is perhaps the role of Hox genes, and specifically their influence on the Apical Ectodermal Ridge (AER). The AER (Figure 23) represents a group of embryonic cells that form at the distal end of each limb bud and are responsible for the proper formation of the vertebrate limb. The AER has been shown to play a major part in the development of both fish fins and tetrapod limbs, but how the AER functions and what mechanism determines whether the finished appendage will terminate in the lepidotrichia of a fish or digits of a tetrapod are issues that have only recently been elucidated. What appears to happen is that, through the influence of the Hoxd complex of regulatory genes, the AER in fish triggers the formation of a fin fold, which is the ontogenetic precursor of the fish fin. In tetrapods, the Hoxd gene inhibits the distal propagation of the AER, so that a fin fold does not form. Therefore, fish already have the ability to develop a tetrapod autopod, but the gene capable of triggering the autopod’s development is not active. This finding effectively puts to rest the notion that the autopod of tetrapods is an evolutionary innovation. Instead, formation of an autopod is simply the result of a change in gene expression, which stops the development of the fin fold, allowing an autopod to develop. In effect, activation of the Hoxd gene permits the encoding of positional information that is necessary for the patterning associated with the development of the tetrapod limb. The entire mechanism is rather complex and beyond the scope of this textbook, but the key difference is that, when the fin fold is not activated, mesenchymal cells that would otherwise not be involved in building the distal portion of the appendage are recruited and establish the scaffolding needed for an autopod to form. The digits of the autopod develop through endochondral ossification of embryonic mesenchymal tissue, whereas in the distal portion of a fish fin the lepidotrichia are derived from dermal ossification of somitic mesoderm. While mesenchyme and somitic mesoderm are distinct tissue types, they are developmentally linked, as both somitic mesoderm and mesenchyme are the biproducts of embryonic mesoderm. The differentiation of embryonic mesoderm is initiated during the process of gastrulation, which is a step in embryonic development. Embryonic mesoderm is just one of three critical germ layers that also include endoderm and ectoderm. The somitic mesoderm is one of the initial derivatives of the embryonic mesoderm and is associated with the segmentation of the embryo that also includes the differentia- From the study of the origin and early evolution of tetrapods we can conclude that, although many stem tetrapods possess a very typical tetrapod limb, the advent of the autopod, combined with other anatomical changes such as separation of the pectoral girdle from the skull, likely took place in an aquatic environment but produced a body plan capable of functioning on land with relatively little further modification. Although Tiktaalik closely approaches the limb anatomy of a tetrapod, as it possesses a tetrapod-like limb axis in which the ulnare is in-line with the proximal portion of the limb, it is still a fish in that it lacks a discrete autopod, the most definitive characteristic of Tetrapoda. However, if additional studies reveal that the five recognized fin radials of Tiktaalik are homologous with the digital rays of tetrapods, then the tetrapod limb axis would likely represent a plesiomorphy present in the common ancestor of Tiktaalik and Tetrapoda. Furthermore, the emergence of numerous additional traits, including separation of the pectoral girdle from the skull (i.e., the development of a neck), zygapophyses, enlarged ribs, and attachment of the pelvic girdle to the vertebral column via a true sacrum, may have been as important as the autopod in equipping the earliest land- dwelling tetrapods to walk and thrive in a comparatively harsh terrestrial environment where buoyancy no longer supported the body against the relentless force of gravity.

Answer 42

the key diagnostic feature of Tetrapoda is not terrestrial habits but rather the presence of an autopod, defined as a manus or pes with endochondrally ossified digits rather than the numerous dermally ossified rays seen in the fins of fish. Ichthyostega is representative of the earliest true tetrapods. Although Ichthyostega is known from relatively complete remains, little information about its manus is available. The pes of Ichthyostega, however, would have been incapable of bending in the manner necessary to facilitate locomotion on land. In a very close relative, Acanthostega, the forelimb and hindlimb are both relatively well-known and again appear too paddle-like and inflexible to have been very useful in terrestrial walking (Figure 19). Although the fact that the limbs of ichthyostegids seem primarily adapted to function as aquatic propulsive organs, it does not eliminate the possibility that they regularly made short ventures onto land; it is likely that these first tetrapods were contribute extensively to movement on land. It also possessed one of the most characteristic features of tetrapods, namely a neck. In fish the bones of the shoulder girdle are directly and inflexibly attached to those of the skull, whereas in tetrapods the two structures are separated so that movements of a series of neck vertebrae can change the position and orientation of the head relative to that of the shoulder girdle. Fish have little need for a neck, as they can turn their entire bodies relatively easily

Answer 43

The diversity of lobe-finned fish far exceeded that of ray-finned fish during the Devonian. Sarcopterygians can be subdivided into three major groups (Figure 11): the Actinistia (coelacanths, including the modern genus Latimeria), Dipnomorpha (lungfish and Porolepiformes), and Tetrapodomorpha (Rhizondontiformes, Osteolepiformes, & Elpistostegalia). A number of additional, less well-known sarcopterygian or at least sarcopterygian-like taxa, including the recently described Chinese taxon Psarolepis and the Silurian form Guiyu, are of dubious taxonomic position and cannot be readily assigned to any of the major lineages. Psarolepis displays a mix of actinopterygian and sarcopterygian features that suggest affinity to each of these groups. In general terms, true sarcopterygians differed extensively from their ray-finned cousins and were already common by the end of the Silurian. The presence of Psarolepis at the Siluri- anDevonian boundary suggests that this taxon was likely not ancestral to either sarcopterygians or actinopterygians, but may instead represent a relic stem osteichthyan. Phylogram depicting the major groups of Sarcopterygii during the Devonian. Note that the Osteolepiformes represent a paraphyletic assemblage that includes all sarcopterygians on the stem leading to tetrapods, other than the nearest relatives of tetrapods

Answer 44

The anatomy of these early ray-finned fish remains primitive in that the skull is a mosaic of numerous individual bones. By contrast, a considerable reduction in the number of skull elements took place during the evolution of more derived actinopterygians into the Carboniferous and beyond. For example, advanced palaeoniscoids possess a specialized skull element known as the dermopterotic, which is the result of fusion between the intertemporal and supratemporal bones found in primitive taxa such as Moythomasia. Close relatives of Moythomasia include the equally well known Cheirolepis and the lesser known Tegeolepis. All of these taxa and many other Devonian palaeoniscoids share a plesiomorphic general body shape characterized by heavy rhomboidal scales, very tightly bound fin radials, and numerous basi-radials (i.e., radials are components of fish fins and their

Answer 45

Osteichthyans (bony fish) are sub-divided into two monophyletic groups, known as Actinopterygii (ray-finned fish) and Sarcopterygii (lobe-finned fish). Both can be distinguished from the Chondrichthyes by the presence of a bony skeleton. The two clades differ in a number of ways, but the most notable difference lies in the structure of the fins. Actinopterygians or ray- finned fish possess a set of slender bony rays, known as lepidotrichia, that extend along most the fin and attach directly to the basal skeletal elements known as the radials, which in turn connect the fins directly to the body, whereas sarcopterygians or lobe-finned fish, while still possessing lepidotrichia, include a number of enlarged bony elements in the fin that separate the lepidotrichia from directly articulating with the body skeleton. As we will see in our introduction to tetrapods, later in this chapter, these additional bony elements are homologous with those of the tetrapod limb.

Answer 46

placoderms were a highly diverse group of jawed vertebrates, which shared a common ancestry with ostracoderms and specifically those taxa that were on the stem leading to the gnathostomes. Superficially, advanced agnathans, such as the osteostracan Cephalaspis, would have appeared quite similar to the heavily armoured, bottom-dwelling placoderm Bothriolepis. However, this superficial similarity reflects little more than convergence, due to a shared benthic lifestyle (Figure 5). Cephalaspis might have fed on small benthic organisms in a manner broadly similar to that of Bothriolepis, but the absence of jaws in the former would have greatly limited the variety of potential prey. Some placoderms belonging to the highly derived group Arthrodira reached the status of apex predators, a role most clearly and iconically exemplified by the monstrous Dunkleosteus (Figure 6).

Answer 47

continuous downward trend in ostracoderm diversity. Although osteostracans (Figure 4) were common in the early part of the Devonian, they were already in decline by the middle of Devonian time. During the Middle Devonian many bodies of water, but especially those that were land-locked, underwent extensive oxygen depletion. Such conditions undoubtedly benefited jawed vertebrates, with their enhanced ventilation capacity. Recall, from the last chapter, that the ventilation hypothesis for the evolution of jaws emphasized the increased capacity for forcefully drawing in greater volumes of water by jawed vertebrates, which in turn increased ventilation. In addition to osteostracans, thelodonts also survived well into the Devonian. The recently discovered thelodont Neoturinia hutkensis, described in 2016, is from the Late Devonian (Frasnian) of Iran – some 375 million years ago. A number of scales and other disarticulated remains of thelodonts were found at this locality, providing further evidence that jawed and jawless vertebrates co-existed for an extended period and thus raises questions as to whether it is appropriate to consider the appearance of jaws as having provided some competitive advantage for those possessing them over putatively

Answer 48

Examination of the pathway proposed by the Neoclassical Hypothesis of jaw origins, which argues that the anteriormost branchial arches went through an intermediate stage in which they functioned to enhance gill ventilation. In this scenario, jaws did not evolve for feeding at all but became coopted for feeding secondarily through contingency alone. This illustration is based on the work of Mallatt, J. (2008). The Origin of the Vertebrate Jaw: Neoclassical Ideas Versus Newer, Development-Based Ideas, Zoological Science, 25(10):990-998-https:// doi.org/10.2108/zsj.25.990 NH supporters argued for the series of evolutionary changes outlined in Figure 15. They postulated that the selection pressure driving initial enlargement of the first branchial arch was a need to improve the ventilation of the gills. This involved more expansive buccal pumping, which serendipitously enhanced prey capture. This enhanced ability to capture prey was simply a serendipitous response to the increased ability of the presumptive jawed vertebrate to increase ventilation. In other words, in order to increase ventilation, it is necessary to expand the volume of the buccal cavity, which in turn results in creating a pressure gradient between inside the mouth and the surrounding environment. This pressure gradient would then serve to draw water into the buccal cavity at an increased rate, in order to fill the increased volume that is now available with the expansion of the jaws. Logically, this increased flowrate would invariably draw in food particles, that would have been nearby, but under normal conditions would not have been available for ingestion. Presumably, one can envision a situation where the hypothetical ancestral gnathostome would not only have increased its ventilatory capacity, but it would have also increased its ability in gaining greater access to food. In effect, the enlarged branchial arch became a more active part of the prey handling system, ultimately developing into the gnathostome jaw. This mechanism differs from the HH in not requiring addition or loss of any significant anatomical structures, instead postulating gradual changes in the function and morphology of existing anatomical structures. Figure 15: Examination of the pathway proposed by the Neoclassical Hypothesis of jaw origins, which argues that the anteriormost branchial arches went through an intermediate stage in which they functioned to enhance gill ventilation. In this scenario, jaws did not evolve for feeding at all but became coopted for feeding secondarily through contingency alone. This illustration is based on the work of Mallatt, J. (2008). The Origin of the Vertebrate Jaw: Neoclassical Ideas Versus Newer, Development-Based Ideas, Zoological Science, 25(10):990-998-https:// doi.org/10.2108/zsj.25.990 The HH requires a great deal more change as it demands that a type of ectomesenchyme known as postoptic crest cells (POC) alter their function. For example, in modern agnathans such as the lamprey, the POC codes for the formation of the upper lip, whereas in gnathostomes the POC codes for the formation of the trabeculae. Its primary contention is that in some putative ancestral gnathostome, a developmental shift led to both the loss of the upper lip and the de novo appearance of the upper jaw. More precisely, the HH postulates that a number of genes (Bmp4, Msx1, Fgf8, and Dlx1) shared by lampreys and gnathostomes are expressed in a more anterior position, along the longitudinal axis of the embryo, in the latter group than in the former. From a morphological perspective, the shift in position is also interpreted as resulting in a shift of the position of the mouth, which in turn leads to the shift in Fgf8 expression. This scenario demands that an association between Dlx gene regulation and the premandibular/ mandibular boundary must diverge when examining the evolutionary history be-

Answer 49

The jawless fish, sometimes placed taxonomically in the Class Agnatha, are now accepted as representing the first successful major evolutionary radiation of vertebrates. Agnathans constitute what is best described as a paraphyletic assemblage rather than a clade, with some members being more closely related to gnathostomes (jawed vertebrates) than others. In other words, gnathostomes evolved from among the diversity of agnathans, as did living myxinoids (hagfish) and petromyzontids (lampreys). These two groups represent the only jawless fish to have lived beyond the Palaeozoic, but some other agnathans persisted until the end of the Devonian, more than 100 million years after the dawn of the Ordovician. FIGURE 5: Conodont “teeth” of the species Manticolepis subrecta (top left); Clydagnathus windsorensis (bottom left), found in Scotland’s Lower Carboniferous strata (the Granton Shrimp Bed) in 1982, was initially misidentified as belonging to the shrimp family. We now know that C. windsorensis represents one of the best-preserved conodonts, displaying soft anatomical features along with the characteristic “teeth”. The entire length of the specimen is approximately 4 cm. The earliest vertebrate relatives are the conodonts (Figure 5), which are overwhelmingly represented in the fossil record by enigmatic, isolated structures that resemble tiny teeth of varying morphological complexity. The term “conodont”, meaning simply “conical tooth”, reflects both the tooth-like appearance of these microfossils and the uncertainty that long existed regarding their true origin. By the

Answer 50

Neodiapsids are characterized by a suite of synapomorphies that are derived relative to the araeosceloid condition. For example, the jugal is slender, and the posterior process tends to be reduced to the point where contact with the quadratojugal is lost. In some neodiapsids, the posterior process is entirely absent, so that the jugal is no longer triradiate. The palate is also modified, the choana being much longer than in araeosceloids and the vomerine process of the pterygoid both longer and more slender. Permian neodiapsids include: Coelurosauravus, a gliding reptile known from a couple of small skulls, and some incomplete post-cranial material, from the lower Permian (Sakmarian) of Germany; Orovenator mayorum, represented by a nearly complete skull; the Guadalupian taxon Lanthanolania ivakhenekoi; and a number of upper Permian forms including Tangasaurus, Acerosodontosaurus, Hovasaurus, Thadeosaurus, Youngina and Claudiosaurus.

Answer 51

Therefore, organisms frequenting lowland areas are likely to die in surroundings where the odds of fossilization are relatively high. In contrast, inhabitants of upland localities that are away from the calm sources of water occurring in the lowlands are less likely to be preserved as fossils. Captorhinomorphs probably occupied upland habitats, and may well be underrepresented in the fossil record for that reason. In fact,

Answer 52

Eureptilia encompass all living reptiles except possibly turtles (see discussion on turtle evolution later in this book), in addition to the vast majority of Mesozoic reptiles. During the Permian, the Eureptilia can be divided into two major clades, one being the Captorhinomorpha and the other comprising the Diapsida and their close relatives. The origins of each clade can be traced to the Carboniferous and even, at least for the diapsid branch of eureptilian phylogeny, to the earliest part of the Middle Pennsylvanian. However, the presence of the captorhinomorph Euconcordia in the Upper Carboniferous, combined with the sister-group relationship between Captorhinomorpha and the diapsid branch that includes Brouffia as its basalmost member, suggests that both eureptilian subgroups originated sometime in the earliest Pennsylvanian (Figure 52). This conclusion

Answer 53

Figure 42: Phylogeny of Parareptilia. The earliest members of this group appear to be the bolosaurids, as Belebey occurs in the Upper Carboniferous. The lanthanosuchoids are a cosmopolitan group, with fossil representatives from North America and Europe. Other parareptiles are known from South Africa, including Millerosauria, the procolophonoid Owenetta, and the Pareiasauria, which are also known from eastern Europe. Procolophonoids represent the only parareptile clade to survive into the Triassic. The Nycteroleteridae are especially noteworthy for their impedance matching high- frequency hearing. Given the phylogenetic relationships depicted above, there must be significant gaps in the fossil record, as a number of parareptile lineages so far known only from the Permian must in fact have evolved during the Carboniferous. The paucity of parareptilian fossil material is not uncommon by Permo-Carboniferous standards, and reflects what is generally referred to as “Romer’s Gap” within the Palaeozoic record. The cause of this gap is hotly debated, but it appears to mark a drastic event when terrestrial life was under significant ecological stress. Based on deBraga & Reisz, 1996, The Early Permian Reptile Acleistorhinus pteroticus and Its Phylogenetic Position, Journal of Vertebrate Paleontology, 16(3): 384-395; Müller et al., 2008, A new bolosaurid parareptile, Belebey chengi sp. nov., from the Middle Permian of China and its paleogeographic significance, Naturwissenschaften, 95:1169– 1174, DOI 10.1007/s00114- 008-0438-0; MacDougall & Reisz, 2012, A new parareptile (Parareptilia, Lanthanosuchoidea) from the Early Permian of Oklahoma, Journal of Vertebrate Paleontology 32(5):1018–1026; & Verrièr et al., 2016, Assessing the completeness of the fossil record: comparison of different methods applied to parareptilian tetrapods (Vertebrata: Sauropsida), Paleobiology, 42(4):680–695.

Answer 54

Figure 39: Comparison of lower jaw morphology between the pelycosaur-grade synapsid Dimetrodon (C & D) and the therapsid Thrinaxodon (A & B). The quadrate (dark blue) is free from articulation with the skull in Thrinaxodon (B), but remains affixed to the posteroventral margin of the skull in Dimetrodon (D). In both taxa, the articular (yellow) is in articulation with the quadrate. In Dimetrodon, the quadrate-articular contact forms the cranio-mandibular joint (CMJ); in Thrinaxodon, this original CMJ persists, but the area over which the quadrate and articular are in contact is small, and the force the jaw joint must withstand is reduced owing to a reconfiguration of the jaw musculature. In Dimetrodon the reflected lamina (light green) is a large ventrolaterally directed flange of the angular (light blue), whereas in Thrinaxodon this structure is smaller and more loosely in contact with the largest element in the jaw, namely the dentary. After Allin (1975), Evolution of the mammalian middle ear, Journal of Morphology, 147(4): 403-437.

Answer 55

Among terrestrial vertebrates, there are two key sensory advantages that mammals possess over most reptiles and birds, namely olfaction and hearing. In particular, the evolution of hearing in mammals has a rich fossil history. The sophisticated hearing complex that characterizes modern mammals began in the Carboniferous, with changes to the lower jaw in the Sphenacodontidae. Dimetrodon, which based on its abundance of fossil material presents as an excellent example, is a sphenacodontid whose jaw has been extensively examined. The primary reasons for this attention are displacement of the jaw joint to well below the tooth row, and the development of an unusual ventrolateral expansion of one of the jaw bones, namely the angular. The lower jaws of early tetrapods are comprised of multiple bones, but an evolutionary trend towards reduction in their number is evident in most amniotes, and in synapsids in particular. The trend has reached an endpoint in modern mammals, in which only a single lower jaw bone is present. However, the nature of the reduction has been the source of much discussion, as it appears to be linked to the evolution of high-frequency hearing capacity in the case of Synapsida. We have noted in previous chapters that a sophisticated high-frequency impedance matching auditory complex has evolved a number of separate times. For instance, amphibians, reptiles (specifically birds) and mammals all appear to have evolved this type of hearing system independently. Among basal synapsids, an impedance matching ear is not known outside the sphenacodontids, in which a ventrolateral expansion of the angular is present and forms a thin sheet of bone contributing to the posterior part of the ventral margin of the lower jaw. This expansion, called the reflected lamina of the angular, would have been capable of detecting vibrations transmitted through the ground, a sounddetecting system that would have been more efficient than the simple bone-conduction mechanism that was likely present in earlier tetrapods including basalmost synapsids.

Answer 56

Nocturnality Modern mammals differ from most other terrestrial vertebrates in that they are active during periods of low light. They are said to be nocturnal, or more precisely can be referred to as scotopic. Scotopic vision is the ability to detect low intensity light. We are all familiar with how domestic dogs and cats seem to have no difficulty seeing in the dark. In fact, 70% of modern mammals are either scotopic (nocturnal) or mesopic (crepuscular); the latter refers to a capacity to see best at dawn and dusk, whereas the former refers to a capacity for vision in very low light. Both scotopic and mesopic taxa require much less light than photopic (diurnal) animals like ourselves. So how do we know which of these light sensitivity categories applied to Permian synapsids? Research published in 2014 used an innovative method to assess light sensitivity, and by extension probable activity patterns, in Permo-Carboniferous synapsids. The method was based on an evaluation of the scleral rings, which comprise circles of small bony ossicles within the orbits. Scleral rings have been lost in mammals, but in reptiles the dimensions of the scleral ring and surrounding orbit are highly informative with regard to light sensitivity, with nocturnal reptiles showing a scleral ring diameter almost equal to the orbit diameter. When Permo-Carboniferous synapsids were examined from the same perspective, the results indicated emphatically that they were primarily nocturnal or crepuscular (Figure 36 & 37). In fact, photopic vision in synapsids does not appear to have evolved until the late Permian and into the Triassic, with the dicynodonts Oudenodon, Pristerodon and Diictodon exhibiting a photopic condition. Aerosaurus wellesi, Dimetrodon milleri, Heleosaurus scholtzi and Sphenacodon ferox, which represent ubiquitous Permian synapsid clades, were all nocturnal, or more specifically would have had scotopic visual capacity. When we consider some of the climatic conditions that we have already noted for the Permian, such as excessive heat coupled with relatively low oxygen levels, it is not surprising that large synapsids may have evolved to avoid the extreme heat of the day and instead be active during nighttime. This finding also raises the possibility of a dichotomy between early synapsids and early diapsids. Diapsids of the Permian were much smaller than their synapsid cousins and may have been more active during the day, as they could have escaped the extreme heat more easily – perhaps hiding in burrows or under vegetation when the heat got to be too much.

Answer 57

Therapsida can be divided into six major clades: Anomodontia, Biarmosuchia, Cynodontia, Dinocephalia, Gorgonopsia, and Therocephalia. All six radiated successfully throughout the late Permian, with three surviving into the Triassic (Anomodontia, Cynodontia, and Therocephalia). Two of these clades, the anomodonts and dinocephalians, were primarily herbivorous, while the other four were primarily carnivorous. Among the herbivorous groups, the anomodonts are more highly derived than the dinocephalians, and underwent a modest radiation throughout the late Permian.

Answer 58

Below is an expanded version of the phylogenetic tree that includes additional groups and subgroups—from early tetrapods through the various amphibian lineages, into the amniote divergence that ultimately gave rise to both synapsids (leading to mammals) and sauropsids (leading to modern reptiles and dinosaurs). This diagram provides a broader context and more details on the evolutionary branching, though keep in mind that many of these relationships remain active areas of research and debate. Tetrapoda │ ┌───────────────────┴─────────────────────┐ │ │ Early Amphibians Amniota │ │ ┌─────────────┴─────────────┐ ┌───────────┴─────────────┐ │ │ │ │ Temnospondyls Lepospondyls Reptiliomorpha Synapsida │ (diverse; potential │ (amphibian‐grade groups (characterized by │ link to Lissamphibia) │ near the origin of a single temporal │ │ amniotes) fenestra) │ ┌──────────┐ │ │ │ │ │ │ │ ┌──────┴─────────┐ │ │ Dissorophoidea Stereospondyli Anthracosauria (Other groups) Pelycosaurs │ (potential origin (large, (stem‐amniotes, (e.g., Dimetrodon, │ of modern amphibians) aquatic) often placed among reptile‐like forms) │ Reptiliomorpha) │ │ │ (Other Reptiliomorphs) │ └─────────────────────────────────────────────────┐ │ │ Other Temnospondyls Lepospondyl groups │ (e.g., Microsauria, Nectridea, │ Aistopoda, etc.) │ └─────────────┐ │ Lissamphibians ├─ Anura (frogs & toads) ├─ Caudata (salamanders & newts) └─ Gymnophiona (caecilians) Amniota │ ┌───────────────────┴─────────────────────┐ │ │ Synapsida Sauropsida │ │ ┌──────┴─────────┐ ┌─────────┴─────────┐ │ │ │ │ Pelycosaurs Therapsida Parareptilia Diapsida (early, reptile-like) (incl. early (basal extinct (reptiles with therapsids, reptile groups) two temporal precursor groups) fenestrae) │ │ │ ┌───────┴─────────┐ │ │ │ │ Lepidosauromorpha Archosauromorpha │ (lizards, snakes, (includes │ tuataras) Archosauria) │ │ │ ┌──────┴───────┐ │ │ │ │ (Other Diapsids) Archosauria │ │ │ ┌──────┴─────────┐ │ │ │ │ Pseudosuchia Ornithodira │ (croc-line) │ │ ├──────┴───────┐ │ │ │ │ Dinosauria Pterosauria │ │ │ ┌────┴─────────┐ │ │ │ │ Ornithischia Saurischia │ │ │ ┌──────┴──────┐ │ │ │ │ Sauropodomorpha Theropoda │ (long-necked (includes Birds) │ herbivores) ⸻ Explanation of Key Branches 1. Tetrapoda & Early Amphibians – Temnospondyls: A diverse group of early amphibians that flourished from the Carboniferous to the Cretaceous. Some hypotheses suggest that a subgroup (such as Dissorophoidea) may have given rise to modern amphibians (lissamphibians). – Lepospondyls: Typically small, with simplified vertebral structures. They include groups like Microsauria and Nectridea, which add to the diversity of early amphibians, though their relationship to living amphibians remains debated. 2. Lissamphibians (Modern Amphibians) – Comprised of three extant orders: • Anura (frogs and toads) • Caudata (salamanders and newts) • Gymnophiona (caecilians) 3. Amniota & the Divergence of Reptiliomorpha and Synapsida – Reptiliomorpha: This grade includes several groups (such as Anthracosauria) that are closely related to the origin of amniotes. These groups help bridge the gap between amphibian-grade tetrapods and true amniotes. – Synapsida: Characterized by a single temporal opening in the skull, this lineage splits early into: • Pelycosaurs: Early, reptile-like synapsids (e.g., Dimetrodon) that dominated Permian terrestrial ecosystems. • Therapsida: More derived synapsids that show increasing mammal-like features. Within therapsids, subgroups such as Biarmosuchia, Dinocephalia, and Cynodontia (from which Mammalia eventually evolved) illustrate a gradual evolution toward the mammalian condition. 4. Sauropsida & the Rise of Diapsids – Parareptilia: A group of basal, often extinct, reptiles outside the main diapsid lineage. – Diapsida: Reptiles with two temporal fenestrae. This clade splits into: • Lepidosauromorpha: Leading to modern lizards, snakes, and tuataras. • Archosauromorpha: A diverse group that eventually gives rise to Archosauria. – Archosauria: Divides into two major lineages: ▪ Pseudosuchia: The crocodile-line archosaurs. ▪ Ornithodira: The group that further splits into dinosaurs and pterosaurs. Within dinosaurs, the two primary divisions are: - Ornithischia: The “bird-hipped” dinosaurs. - Saurischia: The “lizard-hipped” dinosaurs, which include both the massive Sauropodomorpha and the Theropoda (from which modern birds evolved). ⸻ This expanded map integrates additional groups and details across both amphibian and amniote evolution. It highlights the complexity and diversity of early tetrapods, the debated relationships among amphibian-grade groups, and the multiple branches leading to the rich diversity seen in synapsids (and ultimately mammals) as well as sauropsids (including the evolution of dinosaurs).

Answer 59

Important things- Coastline fossils- evidence for plate tectonics Pleycosaurs- primitive synapsids vs eupelycosaurs- more advanced synapsids Thrinaxodon- loss of ribs in lumbar- for flexibility for dorsal ventral flexion underneath ribcage- have diaphragm- this organism prob had diaphragm- important for mammal respiration, need more oxygen due to higher metabolism, endothermic Bones in back of jaw miniaturize and move to inner ear- which ones turn into one- stapes- stapes, incus, malleus – what do they turn into Hybomandibular- fish Sterospondyl- amphibian - in triassic advanced temnospondyl- popular in carboniferous, got hit in end permian- fully aquatic- have a lateral line system only temnospondyl in Triassic, makes past end permian, fill crocodile niche Mastodontonsaurus- large fangs that go through snout, temnospondyl, inpterygoid vacuity- functions to manipulate buccal cavity for brething, manipulates pressure in mouth, force air in and out Suminia- synapsid, leaf shaped teeth for cutting vegetation Phlange of the mandible- related to hearing- hearing low frequency in early synapsids slide 5 feb 5th Synapsids have 2 coronoid process of jaw- defining feature Coronoid processes- articulatins of jaw Dyconodonts- tooth tusk, shrunken face as get more derived- movement of jaw musculature- thought to have big bite force but have beaks to compensate instead, movin of musculature to the backpredentary- synapsomorphy of ornothician dinasours Ornothician dinasours- Heterodontosaurus

Answer 60

Generally, much less common during the Cretaceous. Known only from a few Lower Cretaceous fossils. Lower Cretaceous Wuerhosaurus – possibly a synonym of Stegosaurus – emphasizing the degree to which the material is insufficiently diagnostic. Ornithischia- dinosaurs rare in cretaceous Only thridoria- extensive radiation Synapomorphy- predentary Stegosaurs- 2 diagnosable genera- Wuerhosaurus – fragmentary remains- maybe stegasoarus Less common during cretaceous- Incomplete fossil records Dissepeard at end of cretaceous- when terrestrial evoloution was at high

Answer 61

Appear in Jurassic and become dominant Cretaceous Clade. May have effectively replaced the ecological role filled by stegosaurs during the Jurassic. What information can be extracted from this cladogram? Undergo radiation during cretaceous- one group to do relatively well Other ornithisican dinosaurs Basal ornithicians- survive in cretaceous but undergo decline long before end Diversification of ornithiscians- aligned with KTR- evoloution and proliferation of angiosperms opening niches- sauropoda underwent decline during end of cretaceous 2 separate ornithisican radiation- ankylosaurians- better represenentation of them ,better adapted, nodosauridae- did well but not as well -

Answer 62

Appear in Jurassic and become dominant Cretaceous Clade. May have effectively replaced the ecological role filled by stegosaurs during the Jurassic. What information can be extracted from this cladogram? Undergo radiation during cretaceous- one group to do relatively well Other ornithisican dinosaurs Basal ornithicians- survive in cretaceous but undergo decline long before end Diversification of ornithiscians- aligned with KTR- evoloution and proliferation of angiosperms opening niches- sauropoda underwent decline during end of cretaceous 2 separate ornithisican radiation- ankylosaurians- better represenentation of them ,better adapted, nodosauridae- did well but not as well -

Answer 63

What are the differences?- nodosauridae- lack tail club and have spikes, rely on bony projections along back Is one taxon more successful than its close relative? What are the differences?- nodosauridae- lack tail club and have spikes, rely on bony projections along back Is one taxon more successful than its close relative? Heavily armoured ornithiscians

Answer 64

The prototypical ankylosaurian anatomy! What can we see in this figure? What part of the anatomy are we examining? How does the tail club factor in? A lot of dinasors have ossified tendons- more sturdy, usually made tail more sturdy, have heavy club on tail need sturdy muscles, rigid tail, can smack things with it

Answer 65

What is the primary diagnostic feature of the skull that separates an ankylosaurid from a nodosaurid?- lateral temporal fenestra occluded by ostoderms Hint – visible in all of these figures! What is the primary diagnostic feature of the skull that separates an ankylosaurid from a nodosaurid?- lateral temporal fenestra occluded by ostoderms Hint – visible in all of these figures! Well armoured, sturdy tough What is the primary diagnostic feature of the skull that separates an ankylosaurid from a nodosaurid?- lateral temporal fenestra occluded by ostoderms, rounded crown teeth- herbivores, dorsal vertebrae overlap each other- more rigid less flexible Ossified tendons in distal part of tail

Answer 66

Plot of tooth crown height and skull length Ankylosaurs- distal from regression line and are nosaurid- edmontia and gobisaurus- doing different things Ankylosaurs have smaller teeth- unusual shape of dentition, may have been eating different things, occupying different herbovirous niches

Answer 67

conclusions? Look at the difference in the two nodosaurids (Edmontonia and Sauropleta) when compared to the ankylosaurid Ankylosaurus. Could the Tail Club have served as a weapon? conclusions? Look at the difference in the two nodosaurids (Edmontonia and Sauropleta) when compared to the ankylosaurid Ankylosaurus. Could the Tail Club have served as a weapon? What is club used for- intraspecific combat or defense

Answer 68

Pachycephalosaurs were an exclusively Cretaceous clade. Noted for their domed heads – what have palaeontologists suggested was the function of the unusual skull? What evidence do we have that it was used in combat or for defense? Bipedal ornithiscian dinosaurs with dome on top of head Intraspecific combat? Debate on what use dfome for Intraspecific combat- hemipherisphal shape- not adapting for butting heads, would slide off each other- unlike rams May have been for mating Would these guys of died if rammed into each other- brain bleed- still being debated

Answer 69

Pachycephalosaurs were an exclusively Cretaceous clade. Noted for their domed heads – what have palaeontologists suggested was the function of the unusual skull? What evidence do we have that it was used in combat or for defense? Bipedal ornithiscian dinosaurs with dome on top of head Intraspecific combat? Debate on what use dfome for Intraspecific combat- hemipherisphal shape- not adapting for butting heads, would slide off each other- unlike rams May have been for mating Would these guys of died if rammed into each other- brain bleed- still being debated

Answer 70

22% of examined skulls show trauma that may have been linked to head butting trauma- in adult males Absent in juveniles and females- its only in males- maybe competing for a mate These individuals had traumatic brain injury- was doing this but probably not efficient

Answer 71

Ceratopsia Primarily Upper Cretaceous. Exceptionally successful and species rich. Laurasia origin – appearing in Asia and spreading to North America. Ceratopsia Primarily Upper Cretaceous. Exceptionally successful and species rich. Laurasia origin – appearing in Asia and spreading to North America. Another group of ornithiscians Do well during end of cretaceous Thought to hhave origin in Jurassic Most abundant dinosaur group Poldesnt- yinong Extensive radiation in end of cretaceous, aligned with radiation of pastecians

Answer 72

An early Cretaceous ceratopsian. What attributes/traits in this sma l bipedal ceratopsian can we recognize as ha lmarks of the large quadrupedal Upper Cretaceous forms? One of the most popular early ceratopsian Postural debate and evoloution of quadrupedal from bipedal Has characteristics thought Relationship between premaxilla and maxilla- maxilla is larger Tshaped orbital High position of nasal Dervied feature- no teeth on premaxilla Getting a beak Slighlty expanded shelf for a frill- enlargement of postorbital region to accomadate for processing rough vegetation- seen in triceratops how did it walk? Current accepted view- started as quadraped then moved to bipedal However- may not of had postural shift- forelimbs not a lot shorter than hindlimbs Dinsoaurs have undergone postural shifts

Answer 73

Mosaiceratops azumai Note the expanded postorbital region of the sku l, which is diagnostic of Neoceratopsia. Likely a basal member of the clade Mosaic of primitive and derived charactsristic Stakosaurid- charcateristics- larger premaxilla than maxilla, closed orbital, high position of external naris Derived feature- indentioulous premaxilla- no teeth- defines saurotopsians Premaxilla dentition lost may be synapomorphy- Loss of premaxilla teeth- derived along saurotopian lineage More quadrupedal like, more pronounced frill

Answer 74

Upper Cretaceous (Maastrichtian) of North America. This species probably was primarily quadrupedal, despite being shown here in a bipedal pose. Why would paleontologists believe that this taxon was quadrupedal? Trends towards specializing in fiborous vegetation Larger head than body More pronounced frill Loss of premacilla teeth No predentary teeth Prob both bi-and quadpedial - centre of mass towards front of animal

Answer 75

Key diagnostic traits: 1- prominent nasal horn; 2-teeth with double roots; 3- more teeth in the jaws; 4- shearing dental battery; 5- teeth containing five separate tissue types; 6- sma l dermal ossifications (epoccipitals) along the margin of the frill; and 7- fusion of the anterior cervicals into a syncervical, which would have stabilized the large head and increased its utility as a battering ram. Bigger Key diagnostic traits: 1- prominent nasal horn; 2-teeth with double roots; 3- more teeth in the jaws; 4- shearing dental battery; 5- teeth containing five separate tissue types; 6- sma l dermal ossifications (epoccipitals) along the margin of the frill; and 7- fusion of the anterior cervicals into a syncervical, which would have stabilized the large head and increased its utility as a battering ram. More stabilization of vertebral column to support head

Answer 76

What conclusions can we make regarding the skulls shown here? How compelling is the evidence for sexual dimorphism in ceratopsids? Loss of epocciptila- bony extensions at back of thrill Has supraorbital horns in grown ups Mature males- more ornamentation- ontogentically influenced, also used as horns in buffalo, jesting eachother and fighting for mates- intraspecific combat Ontogenitcally differences- baby different than adults

Answer 77

Ornithopoda Along with ceratopsians, ornithopods are the most abundant large herbivores of the Cretaceous. What information does this cladogram provide? Another group that does well towards end of cretaceous- hadrosauridae - include saurolophinae Origins in Jurassic Ornithopod- modify dentition in cretaceous end- specialized then died during KPG

Answer 78

The general body-form of later hadrosaurs is already evident, but the thumb spike that was diagnostic of Jurassic iguanodontids remains. Quadrapedal Hoof like at end of digits - big toe nails 4th and 5th digits are smaller and lack these hooves Have thumb and thumb spike 2 digits off the ground Later/ most derived heidosaurs- don’t have thumb spike, early ones retain it The arrival of the hadrosauroids in the Lower Cretaceous

Answer 79

Although still plesiomorphically rather similar to Iguanodon in general morphology, Equijubus prese nts a relatively derived dental histology in that the teeth contain additional tissues not seen in more basal ornithopods. Hadrosaurid Derived dental histology- arrangement of bone tissue- have additional bone tissues not seen in basal ones More specialized dentitions Start of it Anterior snout is to left The teeth are not in dental battery Sementum jacket- bone tissue- have it at bottom of tooth

Answer 80

The Hadrosauridae represent in some sense the pinnacle of ornithopod evolution, and members of this derived assemblage can be distinguished from their more primitive relatives on the basis of a suite of synapomorphies including: 1- increased lateral expansion of the premaxilla- do this to have dental battery; 2- substantially greater number of tooth positions, inc surface area; 3- grinding dental battery, resulting in large upper and lower shearing surfaces; 4- complex, unusual tooth microstructure;- sementum 5- fully elaborated pleurokinetic axis between the maxilla and the rest of the skull; - cranial kinesis- related to chewing 6- manual digit I completely absent; and 7- elongation of metacarpals II-IV, further enhancing the locomotor role of the forelimb.- quadraped

Answer 81

Transverse section of an erupted, maxillary hadrosaur tooth. Note the clear separation between the cementum covered side of the tooth and the enamel covering on the opposite side. Dental battery- Sarotypids have 5 seperat tissue these ones have 3 tissues- sementum- anchors tooth to jaw, enamel- outer covering and vascular dentine Enamal- covers outer tooth Dentine undelries enamel In hadrosaur- enamel doesn’t cover all toth- restricted to one side with cementum cobering the other Broad shearing dentary- formed by collection of generation of teeth that replenish grinding surface Dental battery helps replace wore down teeth Lose older teeth instead of retaining them- wouldn’t of had to dental battery- need to retain them Response to new sourve of food- angiosperms- why ornithopoda did so well during late cretaceous Underwent adaptive radiation that changed mastication to eat this new food Grass evoloution also helped among sauropsodians Grinding rough vegetaion

Answer 82

A very flexible skull! Shaded elements are all mechanica ly involved in mastication. Hadrosauridae Have kinetic skull Haded- involved in mastication- maxilla, quadrate, jugal Fully erupted teeth- been attached to bone tissues by periodontal ligament- can absorb compression associated with biting, increased mobility of teeth- helped with kinesis of skull Teeth not cemented in the jaw- flexibility of jaw Pleurokinetic hinge- where bones attach to skull- between maxilla and premaxilla and maxilla and jugal and lacrimal jaw- main one but whole jaw has evolved

Answer 83

Jaw moves forward and back but have lateral movement of the bones as well Quadrate and pyterogoid move together Jaw is moving Jugal and quadratal joint Mandible and quadrate joint Jaw moves to side- upper jaw stable, skull is moving to side

Answer 84

Hadrosaur diverged into lambisordians- perisolarphus- can produce low frequency sounds bc of hollow crest Why?- prob to communicate with each other, mating Crested hadrosaur- at back of head Saurlophians- flat headed hadrosaur Some saurolophians had small crest During inhalation- draw air in lungs then exhale and move air through the crest- sexual selection

Answer 85

Note the differences when comparing taxonomic diversity to morphological disparity. What conclusions can be reached? Note the differences when comparing taxonomic diversity to morphological disparity. What conclusions can be reached? In Jurassic some came well adapted to fast swimming See decline in diversity A- estimated vs observed phylogenetic diversity B- taxic disparity Decline in species type One group makes into cretaceous and don’t make it through end exctinction Distributed geographically- depending on ecological role Some eat soft prey Other eat fish Others apex predators All uniform ichthyosaurs Apex predator survived past boundary- some last ones to go extinct Decline overall Hit hard in Jurassic- never fully recovered

Answer 86

Uniform ichthyosaur- occupy dolphin niche During the Cenomanian-Turonian, Earth was undergoing rapid, significant geographic and climatic change. Polar ice caps were absent and sea levels were fluctuating but tending to rise. Oxygen isotope data show that mean global temperature was increasing. The combination of sea level fluctuations and increasing global temperatures contributed to changes in oceanic circulation patterns that led to oceanic anoxic events, imposing further environmental stress on marine life. The Cenomanian was a difficult time not only for ichthyosaurs but also for many other organisms, with microplankton, belemnites, ammonites, and various reef-building invertebrates all suffering sharp declines in abundance and in taxic diversity. The decline of belemnites and ammonites was probably the primary reason for the early Cenomanian disappearance of the ophthalmosaurines, ichthyosaurs that relied primarily on soft-bodied prey

Answer 87

Uniform ichthyosaur- occupy dolphin niche During the Cenomanian-Turonian, Earth was undergoing rapid, significant geographic and climatic change. Polar ice caps were absent and sea levels were fluctuating but tending to rise. Oxygen isotope data show that mean global temperature was increasing. The combination of sea level fluctuations and increasing global temperatures contributed to changes in oceanic circulation patterns that led to oceanic anoxic events, imposing further environmental stress on marine life. The Cenomanian was a difficult time not only for ichthyosaurs but also for many other organisms, with microplankton, belemnites, ammonites, and various reef-building invertebrates all suffering sharp declines in abundance and in taxic diversity. The decline of belemnites and ammonites was probably the primary reason for the early Cenomanian disappearance of the ophthalmosaurines, ichthyosaurs that relied primarily on soft-bodied prey

Answer 88

Maybe moving into ichthyosaur niche Leptocledia- Only other prominent group in cretaceous pleisosauroidea Both morphologically and taxonomically diverse Some have long necks and small heads Some have short necks large heads Thought to be 2 distinct groups What defines these groups?- know

Answer 89

Long paddles- propel through water Small head- adapted for catching fish Originally grouped with long neck lapisoarida

Answer 90

Pliosaurids (not related to cryptoclidids) Polycotylid cryptoclidids (more closely related to the long-necked leptoclidids) Holotype of the polycotylid plesiosaur Edgarosaurus muddi. Short necked Head is bigger

Answer 91

Short neck Large skull Stiffened torso Cretaceous polycotylid plesiosaur, Polycotylus latippinus, a Campanian aged plesiosaur. The emergence and early diversification of polycotylids coincided with the decline of ichthyosaurs. Coincidence? Emergence of short necks- radiation coincide with decline of ichthyosaur- similar to chuncky ones Maybe filling the vacant niches Confuse with pleiosaurd- short neck larger head Paddles- pronounced compression of phalanges- modifications of flippers to limit drag- compression of hyperphylangated fins More little fnger bones- more phalanges Most derived ichthyosaurs- lose phalanges- thin and can cut through water Pleisousaur- catching up to ichthyosaurs by modifying body Pursiuing soft bodied prey

Answer 92

Kronosaurus – An apex predator with the colossal bite force.- huge head short neck giant animal Note the similarity in bite force calculated for C. porosus (Salt-water crocodile) and Kronosaurus in BOLD. Observe the part of the table highlighted in RED. What is the basis for this data? Bone crushing ability, pursuing apex predator niche

Answer 93

Elasmosaurids- last group of pleisosaurs (Long- necked fish eaters) Dominate the Western Interior Seaway- important, sea level in cretaceous so high, low latitude ateas cut in half, shallow sea cuts fom northwest territories down to gulf of mexico where depth likely never exceeded 500 metres. Contributor to flatness of alberta and stuff Why find a bunch of the marine fossils Waters were warm and tropical and bioproductivity was high, owing to the high levels of nutrient-rich sediments that were deposited by the numerous deltaic environments that dotted the coastlines. Continental shelf conditions- most productive area of ocean Elasmosaurids- sister to cryptocykdia

Answer 94

Mosasaurs (The whales of the Cretaceous!) Marine reptiles that are most popular and successful large teeth on top of mouthh

Answer 95

the shallow seas (light blue) located through what is now N. America and Europe during the Coniacian around 88.5 mya. Europe mostly underwater and tropical areas- environment that allows marine animals to thrive Switch from terrestrial to water- they were thought to

Answer 96

Related to veranids morphologically Squamates before cretaceous- the last period of Mesozoic that they became diverse Major clades came about Most important for squamates- evoloution of mosasaur Phylogenetic debated- maybe closer to veranids, but the closeness is prob due to convergebce Trying to exploit water resources Closely related to snakes Emergence of snakes and lizzards is confusing- mosasaur maybe part of that evoloution They are squamates, similar morphology to veranids- because of convergence but roots may lie closer to liards

Answer 97

The earliest mosasaur Terrestial lifestyle suited limbs

Answer 98

Adapted to swimming On islands Competing for land resources so start to go to water and develop adaptations to pursue aquatic lifestyle Don’t have paddles Prob had webbing digits Long tail- rutter Mosasaur- fins start to develop, tail has fin like the elongate body and short limbs members of the extant genus Varanus be related to mosasaurs? Still has limbs for teresstial lifestyle

Answer 99

Typical mosasaur from the Cretaceous of Kansas. Note the very large thecodont dentition and the mandibular hinge. Pterygoid teeth Conical teeth, large meant for piercing and gripping Ball and socket joint for jaw- permit anterior part of jaw to pivot so have exaggarated gape to, open jaw more and swallow larger organisms Teeth on top of mouth Craonecous Teeth for piercing and gripping

Answer 100

The Streptostylic Skull- highly kinetic skull- intermandibular joint and ratchet feeding Note the incredibly kinetic skull. What other taxa have we studied this year that possess such flexible skulls? What might this flexibility suggest? Cranial kinesis- squamate thing, bones of head can move Improves efficiency of chewing Seven separate joints Intermandibular- modified to form ball socket- to cause wider gape of jaw Rotation of quadate- can allow lower jaw to extend forward Bend slightly when biting on prey- reducing strain on braincase Jaw muscles contract without hurting brain Jaw extends past snout Ratchet deeding- used by snakes Cranial kinesis- used by snakes

Answer 101

Mosasaur paddles. Note how they vary extensively based on preferred habits. The most cetacean-like paddle belongs to the late Cretaceous mosasaur Plotosaurus. More advanced have hyperphalange condition More hydrocaraul fin Paddles Kink in tail- tail fluke Rigid Evidence for aquatic lifestyle

Answer 102

Plotosaurus – The Cretaceous equivalent of modern-day cetaceans Note the long, slender fore-paddles and the fusiform body, which would have been Plotosaurus – The Cretaceous equivalent of modern-day cetaceanscapable of generating speeds sufficient for open water pursuit. The caudal fluke is large and the caudal peduncle is wel-developed. This mosasaur was the fastest of its time and in less than 30 million years had evolved an anatomy that riva led that of ichthyosaurs falling just short of the thunniform morphology which took ichthyosaurs over 150 million years to evolve. Note the long, slender fore-paddles and the fusiform body, which would have been Plotosaurus – The Cretaceous equivalent of modern-day cetaceanscapable of generating speeds sufficient for open water pursuit. The caudal fluke is large and the caudal peduncle is wel-developed. This mosasaur was the fastest of its time and in less than 30 million years had evolved an anatomy that riva led that of ichthyosaurs falling just short of the thunniform morphology which took ichthyosaurs over 150 million years to evolve.

Answer 103

Plotosaurus – The Cretaceous equivalent of modern-day cetaceans Note the long, slender fore-paddles and the fusiform body, which would have been Plotosaurus – The Cretaceous equivalent of modern-day cetaceanscapable of generating speeds sufficient for open water pursuit. The caudal fluke is large and the caudal peduncle is wel-developed. This mosasaur was the fastest of its time and in less than 30 million years had evolved an anatomy that riva led that of ichthyosaurs falling just short of the thunniform morphology which took ichthyosaurs over 150 million years to evolve. Note the long, slender fore-paddles and the fusiform body, which would have been Plotosaurus – The Cretaceous equivalent of modern-day cetaceanscapable of generating speeds sufficient for open water pursuit. The caudal fluke is large and the caudal peduncle is wel-developed. This mosasaur was the fastest of its time and in less than 30 million years had evolved an anatomy that riva led that of ichthyosaurs falling just short of the thunniform morphology which took ichthyosaurs over 150 million years to evolve.

Answer 104

After initial decline during the Santonian-Campanian, mosasaurs recover and come to dominate the Maastrichtian. What finally wiped them out? Meausre of species diversity Globally distributed Went extinct after kpg Inc diversity from end of camodian through to mastrictian- 2 episodes of decline in diversity within the canodian and mid cambanian Sea level- average May have been in decline before extinction Ocean temp was declining by end of early Campanian Hit the halisorians the most- small and medium sized mosasuars Known from western inland sea Occupied coastal Cooling surface temp trend caused the decline in them- no direct evidence inc in surface oceanic temp- restored the diversity of halisorians So temp of ocean surface prob oayed a role Maybe halisorians sensitive to temp change But go extinct at end of cretaceous- maybe cause of cooling? Mosasurs are squamates Go from hand to flipper- hyperphalangation, compression of the phalanges, lose of digits

Answer 105

What can we note from the cladogram shown here? Are there any possible evolutionary scenarios that we can propose? Modest radiation into cretaceous- several make into end Evolved back in Triassic underwent radiation in Jurassic that continued More in lower cretaceous By end of cretaceous- decline in diversity- ornithon clade- evoloution of birds may of caused this- but prob not cause they coexsisted for many years Only in later cretaceous birds advance pterosaurs decline Pterosaur- little evidence in fossil record

Answer 106

-evolution of membraneous wing -divergent pedal digit -prepubis (supports gut) -enlarged skull -hollow bones Compare Triassic- small, big tail, large head, membraneous windg, bipedal digit, modifictation of prepubis to support gut, reduction in bones- modifed to fly, loght weight skeleteon, respiratory, soft tissues of wing Cretaceous- mastered the sky, firm wings compossed of tissues and supported ventrally, reduce drag Compare Triassic- small, big tail, large head, membraneous windg, bipedal digit, modifictation of prepubis to support gut, reduction in bones- modifed to fly, loght weight skeleteon, respiratory, soft tissues of wing Cretaceous- mastered the sky, firm wings compossed of tissues and supported ventrally, reduce drag

Answer 107

Pterosaur Anatomy What is special regarding the fine ultra-structure of the pterosaur wing? Actinofibrils- fibrous element of membrane- well adapted structure to stay firm and fly Hollow jaws supported by bony struts- reduce weight of skull Patagium- wing membrane- soft tissues and actinofibrils along ventral surface- helped maintain stiffnes to prevent flapping around and reduce drag Large pectoral muscles- well ventilated- high efficiency lungs and airsacs through body to oxygenate muscles

Answer 108

Wing- elongation 4th finger. Evolution of Pteroid supported anterior membrane Wing- elongation 4th finger. Evolution of Pteroid supported anterior membrane Pteroid- extension from wrist area that supports wing membrane Specific to pterosaurs

Answer 109

What are the differences between the Triassic and Jurassic pterosaurs (A) and their Cretaceous descendants (B)? Note how fusion of the rib cage and associated pectoral elements reduce movement of the anterior sternum, eliminating elliptical rotation (twisting of the body). Posterior vertebral ribs, sternal ribs, sternum, and prepubis can be distended, alowing for volumetric changes of the thorax during inspiration-expiration. Optimizing efficiency Reduced movement of front of sternum Avoid random movements to reduce drag- stiffen sternum Consolidation of thoracic region to reduce turning Similar to birds Thorax has air sacs Pneumastic bones Contninous air flow through lungs- more energy to fly A- primitive condition, red = movement B- in cretaceous, limited movement and tortion, fused ribcage and shoulder girdle fusing with the sternum Fused neural spines

Answer 110

What did the giants eat? Were all pterosaurs piscivores as historically portrayed? Given where the fossils have been found is piscivory even possible? What does this artist rendering suggest? Giant pterosaurs What did they eat- baby dinosaurs 60 m wingspan- huge wingspan How was it air borne? Could hurdle itself into air using upright stance take off from ground Fossils are found inland- not near cliffs Maybe occupying vulture niche- scavenger Terrestrial stalking

Answer 111

Note the increasing species diversity in the Upper Cretaceous. Best studied group of dinasours- therapods Very diverse- can be grouped into fauna based of geography Compprised birds- emerged in Jurassic Cretaceous- continents splittungf appart Divereged on into cretaceous- separating into different continets Tetenurae- diverged in Gondwana- eventually gave rise to birds Africa and south America

Answer 112

Averostra- all encomposing group Diversify During the Jurassic, the Averostra divide into two main clades – the ceratosaurs and tetanurans. The Ceratosaurs go on to dominate the southern continent Gondwana, whereas the tetanurans although present in the south become the dominant theropod lineage in Laurasia. We will explore the Gondwanan distribution here and in our next lecture we will consider the Laurasian assemblage. Are the two continental assemblages distinguishable phylogenetically or is it simply that various theropod lineages were more common in certain regions?- there is some phylogenetic sugnaliing

Answer 113

Ecologica ly equivalent to some large Laurasian Tetanurans. The Jurassic progenitor of the Abelisauridae is shown above. Earliest known representative (Rugops) is from the Cenomanian of what is now Niger. that is dominant in Gondwana. Headless taxon Sleek, gracile, slender, bipedal Primary component of fauna Teratsour lineage Descended from smaller therapods Give rise to psatesourous Short limbs Large Apex Predators The southern continent’s version of Tyrannosaurus rex, the ceratosaurs. Large representative of satosaur lineage

Answer 114

Largest known abelisaurid. Note the incredibly sma l forearms, which are even more diminutive than those of the unrelated tentanuran tyrannosaurs. Don’t know what the forearms are for Prominent ormentations of head 4 digits

Answer 115

Unlike in many other Cretaceous theropods, there appears to be no indication of feathers, or indeed of epidermal integumentary filaments of any kind. The most striking feature of Carnotaurus, albeit one shared with all abelisaurids, is its diminutive forelimbs. Carnotaurus had a robust neck, which lacked the distinct S-curve so typical of theropods. Its neck was instead straight and heavily ossified, undoubtedly to withstand the large forces produced by the large muscles that would have been needed to support the heavy skull. The neural arches of the cervical vertebrae possess large, dorsolaterally directed processes, referred to as epipophyses, which are found in many theropods, but are exceptionally prominent in Carnotaurus. The proximalmost caudal vertebrae have similar dorsolateral protrusions, albeit in the form of transverse processes. Together with the neural spine, these ribs give the upper part of the neural arch a W-shaped appearance in anterior or posterior view. This unique arrangement of the caudal ribs (refer to Figure 52 in the textbook) presumably accommodated a voluminous caudal musculature, ventral to the caudal ribs, and would have served to forcefully retract the hindlimbs, generating significant propulsive power. What would this caudal anatomy have been capable of supporting?- has strong muscles designed to allow it propel itself quickly, appears to be a runner We have skin impressions Big muscular tail, neck and legs

Answer 116

Caudal vertebra of Carnotaurus sastrei (MACN-CH894) in left lateral (A), anterior (B), and dorsal (C) views. Note the dorsolatera ly expanded transverse processes, which form the lateral wa ls of paired V-shaped troughs that would have accommodated expanded caudal musculature. W shape Neural spine B- transverse processes that connect to ribs Need muscles to attach Examine the difference between the two interpretations for the size of the caudal musculature shown here. Which muscle is the largest and what implications does this size suggest? Provides an overview of how orientation of caudal ribs allowed for the support of the tail and rigid body- make it effective for locomotion Vertebrae could interlock- prevent it from slowing down- stabilizing proximal portion of tail Allowing them to go faster Cant bend tail- cant turn quick- cant get agile prey Could of targeted large prey or scavenger- seems inconsistent- designed to run down prey

Answer 117

the massive contribution of the the m. caudofemoralis and the m. ilio-ischiocaudalis. What purpose might this have served? How confident are we in any assumption that might arise? How do we test this putative hypothesis? Vertebrae Muscles attach underneath the tranverse process of the ribs Limited area- m spinalis and longissiumus- quite small, have reduced size, limited to top, function as stabilizers- bend tail laterally and dorsally- wants to reduce this movement so reduce the size of these bones Size- determine how strong force is Note the different percentages of muscle mass attribute to the m. caudofemoralis compared across four separate theropods. What do we notice?- ilio and caudo- represent major body mass in Carnotaurus- enhanced sprinting speed Look at muscles tell them what kind of hunter they were

Answer 118

While certainly not as speciose in Gondwana as their relatives from Laurasia, some interesting morphologies bear consideration. Spinosaurus and Suchomimus are the best known and perhaps present the most intriguing anatomy. Note the very long, narrow snout in Suchomimus shown here.

Answer 119

Why it’s important to look at the entire anatomy before jumping to conclusions. In the Jurassic Park franchise of films, Spinosaurus is depicted as an even more ferocious predator than Tyrannosaurus rex. In fact, in a dule between the two, Spinosaurus comes out on top. Let’s take a close look at Spinosaurus and assess the truth of that narrative.

Answer 120

Long- slender sku l with extensive lengthening of the pre-orbital elements of the skulls. External nares (nostrils) placed high on head. Many conical teeth that are not laterally compressed. Ta l dorsal sail. Large hands with strongly recurved claws. Relatively short hindlimbs. What do a l of these anatomical traits suggest? Are there any that appear to contradict the behavioural role suggested in the Jurassic Park film? Spinosaurus

Answer 121

Note the proportions of the elements of the skull and note specifically the premaxilla as it differs across all laxa • What do you see with respect to the premaxilla in Spinosaurus (skull at the bottom)? Elongation of maxilla area Large conical teeth lacking compression- punctured prey Aquatic affinity? Moving external nares to top of head- common for aquatic vertebraes

Answer 122

Could Spinosaurus have been aquatic? What might the role of the sail have been if Spinosaurus was indeed an aquatic theropod? Life reconstruction of Spinosaurus. Big deep tail S shape neck expanded dorsal spine Argued to be aquatic – prob just hung out near water

Answer 123

The best-known members of the clade include Giganotosaurus, Mapusaurus, and Carcharodontosaurus. All are large and possess serrated blade-like teeth. Compressed narrow teeth Serrated teeth to slice prey

Answer 124

The crowns of the teeth are large, measuring between 60 and 80 mm in height, and in fact are equivalent in size to the teeth of Laurasian tyrannosaurids (Fossil tooth of C. saharicus). How do these teeth differ from those of Spinosaurus and what do these differences support? Metorlateraly compresed- causing serrated teeth Ecological equivalence- have convergence between tyranosurs and caratonosours

Answer 125

The crowns of the teeth are large, measuring between 60 and 80 mm in height, and in fact are equivalent in size to the teeth of Laurasian tyrannosaurids (Fossil tooth of C. saharicus). How do these teeth differ from those of Spinosaurus and what do these differences support? Metorlateraly compresed- causing serrated teeth Ecological equivalence- have convergence between tyranosurs and caratonosours

Answer 126

largest of the known charcarodontosaurids. Common in the Cenomanian but were extinct by the end of the Turonian. Most tetanurans that survive past the Turonian are smaller coelurosaur theropods. Can you think of any reason why this might be the case? Temporal separation for animlas doing the same thing

Answer 127

The last surviving relatively large tetanuran theropods of Gondwana were taxa such as Aerosteon. Noted for their exquisite preservation and the extensive pneumatization of the skeleton.

Answer 128

Pneumatic chambers in the skeleton of Aerosteon. Sections in pink show the camellate (honeycomb-like) pneumatic chambers that are interspersed throughout the skeleton. How does the pneumatization of the skeleton help palaeontologists work out the physiology of these theropods? Reduce body weight inc metabolic efficiency May of flew Bird like mode of ventilation Air sacs permeated much of the skeleton Is pneumacity a saurichian quality- is it ancestral or independently evolved

Answer 129

Albian age Mirischia is one of the earliest known members of the clade. Other taxa include the advanced tyrannoraptoran coelurosaurs: Buitreraptor, Patagonykus and Rahonavis. Patagonykus is notable as it represents a member of the Alvarezsauria,- widespread at end of cretaceous a group that is very common in the Late Cretaceous of Laurasia, but appears to evolve in Gondwana. Most bird like

Answer 130

The sku l is highly elongate, with a laterally compressed snout that contains many small, recurved, unserrated teeth. The absence of serrations suggests that the teeth were more likely used to pierce and grip than to slice and cut. The diet of Buitreraptor has duly been interpreted as comprising smal prey items, possibly including insects, sma l lizards and even mammals. Its gracile proportions would have enabled it to run fairly fast, and its long tail would have acted as an effective counterbalance to help it turn quickly while in pursuit of prey. Reptoral pedial claw- hold prey down

Answer 131

Diverse theropod assemblage that included many of the representatives of the Laurasian theropods that we will explore next lecture. notable difference is that the Large Apex predator role appears to have been played by the abelisaurids as opposed to the tyrannosaurids that filled the equivalent role in Laurasia.

Answer 132

Theropods were effectively separated into Gondwanan and Laurasian forms, but what was the basis for this separation, and did any anatomical features evolve convergently in both geographic groupings? What key attribute of the giant Gondwanan theropod Carnotaurus suggests that it was a fleet-footed hunter, and what further evidence supports this interpretation? Was Spinosaurus a terrestrial apex predator occupying essentia ly the same niche as Tyrannosaurus rex? What are the main arguments for and against this view? Theropods were a very diverse clade of predatory dinosaurs throughout the Cretaceous, some being sma l and agile while others were enormous – what were the typical anatomical differences between taxa in these two broad categories?

Answer 133

Pulses of sauropod evoloution- early starts in end of Jurassic, make it to upper cretaceous Second pulse- more substantial radiation of mostly Titanosaura- big sauropods, largest terrestrial animals- in the cretaceous

Answer 134

Sauropods didn’t get less diverse- early ones replayed by newer ones Absence in fossil evidence- preservational bias, not extinction of these early sauropods Appears theres two pulses but was more of a gradual change Titanosarouforms Brachiosauridae- start in Jurassic

Answer 135

hindgut processors obligate quadrupeds -evolve gigantism -respiratory specializations -physiologically enigmatic -evolution of osteoderms- armour (titanosaurs) Get big and eat herbivores

Answer 136

The first pulse occurred in the Jurassic and produced the popular diplodocoids, which survived into the Turonian Age of the Late Cretaceous; the equaly wel-known brachiosaurids, which persisted into the Cenomanian. The second pulse was an extensive radiation that occurred from the Barremian to the Albian, during the Early Cretaceous, and has been well documented only over the past couple of decades. A brachiosaurid standing by the water’s edge – Note the long forelimbs typical of the clade.

Answer 137

Dominant sauropod clade during the Cretaceous. • All characterized by longer forelimbs than hindlimbs - a trait that was likely shared with brachiosaurids, their common ancestor. • Why might this tendency for increasing forelimb length have been selected? • Can you develop an argument or hypothesis to test your assertion? Groan eding envelope, can get 1 more fod, nreased waking tendey and ably, better stably, high All titanosauriforms have longer forelimbs Specialist consumer of giant trees- genospperms- redwoods Inc vertical feeding reach Get taller to reach them and avoid getting eaten Notes Earlier diverging titanosaurs

Answer 138

Vulcanodon- biggest sauropodomorph- has digits In ancestral condition- lots of small bnes in foot As move up- reduction in phalanges, more robust metatarsal- get longer Titanosaur- no phalanges- walking on knuckles kind of and bones are larger and chunkier- columnar Loose it for weight distribution- like elephants Adaptation for gigantism

Answer 139

This animal competing with other herbivores and only slightly bigger Sauropods- keep forest back- living on edges of forests - have youngest trees- able to eat them Maintain forest boundaries

Answer 140

Exterbal naris at front- more on top- primitive

Answer 141

Examine the figure shown here. Medial (A) and lateral (B) views of the premaxilla and maxilla of the Cretaceous sauropod Euhelopus zdanskyi. Note the procumbent teeth, set at an angle of nearly 45˚ to the alveolar margin formed by the maxilla and premaxilla. What is the relevance of this dental arrangement? Complete skull- rare Big animal Snout is short Peg like teeth- stripping vegetation from branches Differ brom basal sauropods- have a buttress More robust teeth Fed on broad range of vegetation Naris- high on head- seen in Jurassic sauropodomorphs- common trend Upright neck- longer forelimbs- high browising sauropod Percubut teeth- angled out Teeth act to rake vegetation

Answer 142

The internal architecture of the sacral vertebrae is described as camellate! Wat does this mean?air pockets in bones- therapods also have, reduce wieight of skeleton, body mass so can grow bigger Sauropods, including even most early members of the group, display anatomical features whose apparent function was to reduce overall body mass.- reduce of sacral vertebrae Does the camellate morphology have something to do with reducing overall body mass? Does the camellate morphology contribute to pneumaticity? Saurpods- nemasoty- air pockets in vertebrae Starts in sacrum as move up phylogency- most of vertebral column

Answer 143

Pneumaticity could certainly have helped with weight reduction. Unlike early reconstructions of these behemoths, it is now recognized that sauropods used their long necks and tails to balance their bulk over their hips. Centre of mass- in the stomach area

Answer 144

Many advanced sauropod vertebrae are deeply excavated resulting in a honeycomb –like internal architecture. Look at the cross-sections shown here – what does each figure depict? Air pockets in vertebrae- pnemasity Pneumatic chambers in basal sauropods- lack the extensive air pockets Develop cammelate structure- pnemasity throughout vertebral coloumn In basal- in sacrum only

Answer 145

Could heat maintenance have been responsible? If so, what is the evidence? What do we know about the Cretaceous climate that might shed light on a plausible explanation? What environmental events were taking place during the Cenomanian-Turonian boundary, approximately 100 mya, around the time titanosauriforms were apparently undergoing a radiation? Post cranial pneumatozation May have had thermoregulatory function Eleviate heat stress- air pockets wpuld of reduced mass and dec metabolic cost of locomotion Less heavy, less effort to move, costing less energy Climatic event that may of driven this- cretaceous thermal maximum- 100 million years- when titanosaurophorms go under radiation Got hotter at this point

Answer 146

Pneumatized regions of the skeleton (in grey) in two Cretaceous sauropods, a diplodocid (Katepensaurus, above) and an advanced, saltasaurine titanosaur (below). Note that the titanosaur has a much more extensively pneumatized tail, and a pneumatized shoulder girdle. The increased pneumaticity likely evolved in association with the large size of titanosaurs, which would have caused members of this group to experience more severe heat-related stress than the generally smaller diplodocids. Starts in sacral vertebrae then moved to the rest of the body- in titanosaurs- even hips and ribs Pnemacoty- prob primitive Jurassic to cretaceous- gets hotter causing them to need to do this

Answer 147

Osteodorms in titanosaurs- osifications of dermal layer Most advance titanosaurs For defense Some were smaller- exposing to greater risk of predation- have large therapods that prey on them Scutes armour- differ in size and shape larger= oval and short spike on midline- arranged in rows- on the back Smaller- fill in gaps between larger ones- Why would armour evolve in sauropods? Would it be a means of developing protection from predation? If so, why evolve so late during the Cretaceous? Weren’t sauropods being hunted by theropods before the Cenomanian?

Answer 148

Sauropods diversified, with new clades emerging as others disappeared, but why did Gondwanan sauropods succeed even as their Laurasian brethren died out?- prob just lack off fossil record How does armour appear to have aided the survival of the titanosaurs? Did sauropods evolve skeletal pneumaticity separately from theropods? What are the implications of the presence of pneumatic chambers in sauropod bones? Sauropod- fossil evidence incomplete- forst and second pulse

Answer 149

The weasel-like predator Repenomamus robustus – even dinosaurs weren’t safe! Get started in Triassic and do okay in Jurassic- not in high predatory niche In cretaceous- are bolkder and have better fossil representation Looks like a weasel but isn’t Size of a badger – Repenomamus from china Hunt small dinasours, go after the eggs

Answer 150

Overview of mammalian phylogeny- cretacpus Have roots in paleozoic- synapsds, therapsids Crown mammalia- all extant members and most common members Evolvced during Jurassic by cretaceous 3 mjor lineages well established Allotheria- common in jurasic- less diverse Allotherian members- ressemble modern rodents Multituberculate- make it to cenazoic- one of oldest mammalian lineages Their niche today is filled by rodents

Answer 151

Comparison of estimates, from two separate analyses, of the times of earliest divergence within various mammalian clades. • The last column gives the difference between each pair of time estimates. • The most notable difference between the two methods is the absence of a statistically significant signal indicating a delayed increase in the diversification rate of placental mammals. 2 major hypothesis of diversification in crown mammalian Main extent- radiated after cretaceous end exctinction, after dinasours wiped out mammals diversified and filled their niches, 2nd theory- delay and stagnant diversification- not a big boom, already started to diversify

Answer 152

Fossil evidence of cretaceous period mammals- not a lot But some do appear before mass exctinction- placental mammals- before extinction Primates and rodents could have evolved 85 million years ago, no later than 70 million Diversification may have been underway during late cretaceous, before late cretaceous Crown placental and dinasours may have co-existed The climate and the geophysical events during this time- led to inc in diversity and more diverse looking organism Angiosperms- evoloution started 100 million years ago= linked to radiation of mammals angiosperm- flowering fruit producing plant- would of provided novel niches Mammals started after emerging of angiosperms Event- creatacoues terresdtrial evoloution- KTR- emergence of angiosperms and its radiation- linked to radiation of mammals This, the climate and ongoing c hnage of continents helped early mammals diversify Food emerged- then have mammals Comparison of estimated times of earliest divergence within selected mammalian clades in the Late Cretaceous and Cenozoic. Coloured bars associated with individual clades indicate minimum and maximum divergence time estimates, while circles indicate mean estimates.

Answer 153

Stem mammals – monotremes have survived to the present(platypus) Eutricondonts – an early offshoot from the therian stem appear in the Lower Cretaceous and remained common from the Valanginian up through to the end of the Aptian a span of some 30 million years. Some representatives continued into the Upper Cretaceous, such as the taxon Alticonodon from the Campanian of Alberta (e.g., isolated dentary fragment and a couple of molars). The group of montremes- ostralacophins Not well known Weird early diverging group of mammals Origin is hard to pinpoint Lack strong diverse fossil record 30- 100 million years ago- started Kind of a mystery

Answer 154

unique Dentition) All members of this clade can be distinguished from other mammals on the basis of their molariform dentition, which displays a pattern intermediate between those seen in more basal mammaliaforms such as morganucodontids and in crown- mammals more derived than Eutriconodonta. The dentition of eutriconodonts is described as amphilestid-like, which refers to the obtuse angle formed by the molariform teeth. The arboreal Jugulator (seen here) Product of early stem radiation within crown mamallia- Jurassic Molariform denition Arborial- live in tree eat small vertebrates

Answer 155

Repenomamus giganticus- genus, the larger of two species, had a body length of 1 m and a mass of around 12-15 kg. It was considerably larger than almost any other crown-mammal of the Cretaceous, and was about the size of a large racoon. Includes larger carnivores Medium sized dog- larger than most crown mammalian groups

Answer 156

Moving up the stem toward Theria. Some of the largest Cretaceous mammals were allotherians. The taxon Taeniolabis which survived the end-Cretaceous extinction would have weighed as much as 100 kg. Unique dentition- ridges and partitions of teeth Make it past cretaceous Replaced by modern rodents similar to capybara Early diverging mammal; group Thrived in Jurassic- scanscoreal- living in trees End of cretaceous- only multituberculates living- ones like these Mammals- reasonably diverse in cretaceous- before extinction Fourth premolar- tubercular morphology Mystery to why they lasted so long- and why did they die off Survived end cretaceous- arborial- may of expanded into vacant niches after extinction- some already practiced these behaviours, and only sped upo the radiation that was already on way placental mammals- rapid diversification and radiation after cretaceous extinction

Answer 157

Metatheria + Eutheria Present in modern day Mammalian dentition- incisors, molars, canines

Answer 158

Metatherians more commonly known as marsupials arrived in the Lower Cretaceous, but it is likely that their divergence from Eutherians (placentals) would have occurred during the Jurassic, • Nearly complete, articulated postcranium of the Cretaceous metatherian Asiatherium reshetovi, from the Campanian of Mongolia. Notes What is theria Doesn't have lumbar ribs- has lumbar, dorsal and sacral area of vertebral column- associated with articulation Mammals- loose ribs and have vertebral column

Answer 159

As with all mammals the dentition is the most diagnostic feature. “You are what you eat”! Metatherians and Eutherians differ in the arrangement of molars and pre-molars, but are otherwsie quite similar. Observe the molariform dentition in Asiatherium- early metatheria here. Palatal view Disideous pre molar Have 4 molars 3 molars- eutharians No more than 3 premolars – metatheria Basal therians- 4-5 pre molars

Answer 160

Didelphodon from the Upper Cretaceous of North America. The prominent slicing dentition within the heavily-built skull is reminiscent of the carnassial teeth of modern eutherian carnivores. Didelphodon was a relatively large predator, reaching about 1 m in length, and might have been partially aquatic. If so, it may have resembled members of the otter family, to which it is not closely related, from an ecological standpoint. Strong head able to withstand pressure Crown mammalia evolved in Jurassic- but best fossil record is in cretaceous

Answer 161

The metatherians of the Early Cretaceous were shrew-sized at most, with an average estimated body mass of less than 20 g. However, their Late Cretaceous counterparts were considerably larger, with average estimated body masses nearing 200 g and some taxa, such as Didelphodon, reaching around 5 kg. Most of these Late Cretaceous metatherians have been interpreted as scansorial (i.e. able to climb trees and living in trees) and likely would have benefited from the abundance of forest cover during the Late Cretaceous flora.- because of KTR Insectivorous, some may of fed on diverse fruit Upper cretaceous taxa- have dentition good for crushing, ate fruit Largest ones would have scavenged, hunted and ate plant matter- omnivore- raccon, possum Small ones- eat more dainty and larger- eat wjat they can find

Answer 162

Radiating as cretacoues came to close, but by beginning of palosceen- diversity was loss due to mass exctinction Little attention on extinction of mammals during this time, most evidence points to them benefitting from this extinction Smaller= burrow more, can help them survive, more metabolically effivent

Answer 163

Eutharians- specialized for burrowing and metatherians go under massive radiation after KPG After KTR- have radiation of mammals- particulary in herbivore The Cretaceous Terrestrial Revolution, which was associated with the appearance of angiosperms (flowering plants) some 100 million years ago appears to have impacted vertebrate diversity quite extensively. How were metatherians impacted?

Answer 164

- North American/Eurasian origin - North American/Eurasian origin Radiation into Southern Continents Northern extinction, southern diversification Gondwanan distribution (except for possums) South America- retained more tropical floura- contributing to metatherian distribution during KPG North American fauna less strong and went out after kpg Have origin in north America and then radiate and because cretaceous was tropical- once that environment was gone- went to south America

Answer 165

Metatherians appear to have been radiating as the Cretaceous came to a close, but by the beginning of the Paleocene much of their diversity had been lost. Could much of this decline have been caused by the K-Pg mass extinction? Studies of the extinction have tended to focus on how it affected the dinosaurs and many of the other dominant reptile lineages of the Mesozoic, and the impact of the extinction on mammals has received little attention by comparison. What does the evidence show? Demise of them was pure chance event Greater success of eutharians- matter of luck

Answer 166

Fossil skeleton of the early eutherian mammal Eomaia scansoria from the Lower Cretaceous Yixian Formation of China. This taxon has been interpreted as arboreal, and is one of the earliest known eutherian mammals. Note the dark, fuzzy material that surrounds the body of the fossil, and which on closer examination can be seen to represent preserved hair- soft tissue preserved. Fossil skeleton of the early eutherian mammal Eomaia scansoria from the Lower Cretaceous Yixian Formation of China. This taxon has been interpreted as arboreal, and is one of the earliest known eutherian mammals. Note the dark, fuzzy material that surrounds the body of the fossil, and which on closer examination can be seen to represent preserved hair- soft tissue preserved.

Answer 167

Eomaia is remarkable in retaining preserved hair (the dark, fuzzy-looking material visible in Figure 38 of the textbook and the rpeviosu slide). Preserved hair has also been noted in fossils of non-eutherian mammals (e.g. the eutriconodont Volaticotherium antiquum) dating to the Middle Jurassic. It is quite likely that hair appeared very early in the evolution of mammaliaform synapsids- not fur coat but some kind of hair

Answer 168

Eomaia shares a suite of eutherian synapomorphies including: 1- fused pelvic elements (ilium, pubis, & ischium); 2- vertically deep pelvis, as in Zalambdalestes, Ukhaatherium, and multituberculates; 3- short pubic symphysis; 4- patella associated with the knee joint; 5- well-developed medial astragalo-tibial facet that is distinct from the laterally positioned astragalo-tibial facet; 6- modified navicular that is distinctly separate from the astragalar neck; and 7- entocuneiform is long and articulates with metatarsal I, via the joint that is formed between the intermediate cuneiform and metatarsal II

Answer 169

Elongation of distal tarsals-yellow and blue except in multituberculate(primitive) The theria- superposition of astralagus and superimposed calcageus- foot is splated Theriforms- superposition of astralagus and calcenum and lateral position of the phalanges Theria- elongation of tarsals Placental- fully functional morsi-ankle joint- mortisitenon

Answer 170

If we accept that Eomaia and Juramaia are eutherians, then there is a pronounced ghost lineage that exists between the fossil record of these two taxa and the fossil record for the Campanian aged taxon Ukhaatherium (Refer to the cladogram earlier in this presentation). If, however, Eomaia is placed at the root of Theria, then the Campanian taxon Ukhaatherium becomes the oldest known bona fide eutherian mammal (Figure 29). This second evolutionary scenario eliminates the 40=million-year gap that would otherwise result and would imply that divergence between Metatheria and Eutheria took place in the Early Cretaceous rather than the Middle Jurassic. Which of these alternative hypotheses fits best with the fossil record?- early cretaceous diverging- more likely, doesn’t support middle jurasic emergence

Answer 171

Modern mammalian clades continued to diversify, as relatives of the extant Monotremata, Marsupialia and Placentalimade their appearance • The evolution of Mammalia appears to have been very closely linked to the evolution of flowering plants, and mammals increased dramatically in taxic diversity from 100 mya to near the beginning of the Campanian (approximately 80 mya), the approximate time interval during which flowering plants emerged • Eutriconodonts, early members of crown Mammalia, diversified through the Early Cretaceous but appear to have gone extinct by the Campanian • Some eutriconodonts, such as the camivorous but otherwise rather flying-squirrel-like Jugulator, evolved startlingly similar phenotypes to those exhibited by some modern mammals • Allotherian mammals, the group that includes multituberculates, diversified during the Cretaceous and survived through into the Cenozoic before going extinct • Metatherians (marsupials and their relatives) diversified as a widely successful, primarily Gondwanan clade, with some taxa developing a dentition suitable for fruit-eating in response to the rise of flowering plants • Early eutherian mammals diversified, and the exceptionally well-preserved remains of the Chinese eutherian Eomaia provide insight into Mesozoic mammalian physiology

Answer 172

Cartilaganous fish- sharks Fish diversity established by cretaceous- all living clades on cusp of major radiation that continues to modern era Two clades of neocellachi Some members primitive to this group still around in deep water Hexangephprm- still arpund- six gilled shark Skates and rays- most diverse in these clades Make up foundation foe the sharks still living today

Answer 173

Two Major Clades present-day perspective the most well known. • What might have resulted in the galeomorph radiation in the Upper Cretaceous? • Were sharks outcompeting some of the marine reptiles? Photograph of the extant tiger shark (Galeocerdo cuvier). Note the dark, mottled colouring of the upper part of the body, which is typical of the species. The white belly is common to all predatory sharks. Notes Galesmerphi- look like sharks we know Some can tolerate less salty water- swim in any fresh water- started during this time Can find patch of area that is safe to lay their eggs- today and during this time The ability to reside in any water- probably helped them survive during the extinction of cretaceous- maybe why they radiated in this period too Stable climate at this time Coming out of jurasic – reptiles didn’t do good – genetle bottleneck in achesours- populatopn so diminished- no genetic diversity cant support the population- develop defects- inbreeding Shark lineage is older than trees Probably did outcompete the reptiles and found their niche

Answer 174

While there were some large predatory galeomorphs during the Cretaceous, some specialized on smaller prey. The ancestor of the modern whale shark and even some of the benthic – bottom feeder-feeding rays were also abundant. Sharks and rays were a rather diverse clade and many of the modern groups became established at this time. The batoids (rays) were very diverse with many species occurring in the shallow seas that inundated what is today France and the British Isles.- Europe was underwater during this time- shallow water- diverse area that allowed marine life to thrive Several types of sharks that do different things

Answer 175

Shark tooth diversity before the K-Pg boundary (Maastrichtian) – before vretacious extinction and after the boundary and mass extinction event (Danian). Note the absence of broad triangular teeth in the post-extinction Danian. The Maastrichtian sample contains approximately 350 teeth, around 270 of which represent robust morphotypes. The Danian sample contains approximately 160 teeth, but no robust ones. The differences between the two samples suggest that the lamniform sharks that existed following the end- Cretaceous extinction were generally smaller than their predecessors and had undergone a major shift to a primarily fish-eating habitus. Case study Morphology of teeth Vertical axis- number of teeth within sample Don’t have morphology the same after extinction Shift in morphology of teeth pre and post extinction- change in habit and prey- eating smaller fish(slender teeth)

Answer 176

During this period major bony fishes appear Because of geophysic changes- Europe supporting marine life Increasing shallow coastal environments, increasing radiation of fishes and green reptiles Each major group underwent renaissance- did very well Cretacous may be the time when they do the best Stable environment and major marine environemt Lungfish- sepearet into 3 genera- south Africa, America, antartica- where in guadwana before break up of pangea Adedicant- lobe finned, Bony fishes did well and diversified and wnet to cenazoic

Answer 177

Some bony fish during the Cretaceous were exceptionally large. Fossil skeleton of the large ichthyodectiform Xiphactinu s. This fish would have resembled a modern tarpon, and had large, sharp teeth that would have been capable of inflicting severe wounds on its prey. As with all fish, it would then have swallowed the prey whole, even if the prey was relatively large. Note the complete skeleton of a large fish, measuring more than 1 m in length, inside the abdominal cavity of this specimen. Some got rlly big- bony fish Fossil skeletal remains Find whole fish in its body cavity Dies by choking on what they eat Swimming in open and shallow ocean

Answer 178

The Elopomorpha have an interesting anatomical feature that resembles the alien from Hollywood fame. Pharyngeal Jaws that can be extended to help capture and ingest prey. Diagram of extant moray eel, displaying the “pharyngeal jaws” that are found in some elopomorphs. These additional “jaws” can be protruded to help in manipulating and swallowing prey. Pharyngeal jaw in back of jaw, open mouth can extend these secondary jaws firther out Derived structure, no orher fish has this Emmerged during this time Eels- flexible and smart

Answer 179

Many of the major groups around today were established. Of all of the clades, the Percomorpha are the most diverse clade of bony fish today and while they were established during the Cretaceous, they were less wide-spread. Within the Percomorpha, the Perciformes has become the most diverse assemblage accounting for over 40% of all extant bony fish species.

Answer 180

Fossil record is limited but representatives of the three extant groups were established.- frogs salamanders and cicilians Their diversity during the Cretaceous was sensitive to climatic fluctuations as it is today. A and b- ratio of extinction vs origin Synapomorphy of lissamphibians- pedicalate teeth some dissorophoid have this- maybe temnospondyl the ancestors of Lissamphibia Cecilians where do they come from Amphibians- most sensitive to climate change B- diversification of amniotes and amphibians Green and red- amniotes Cretacoesu- lissamphibians sensitive to climate change Lissamphibians- (similar To today) right now are very sencitive to climate change, more than amniotes Today extinction of amphibians is much greater than any time in history

Answer 181

By beginning of cretaceous- modern amphibian groups are established- including salamanders, frogs and caecilla Pedicilate teeth- one group of temnospondyl also have

Answer 182

Best urodele – widely spread, 3 genera fossils Come from the Jehol Biota of the Jurassic- Cretaceous of China Preservation of soft anatomy alongside skeletal- live in muddy shallow water- get better fossils Fossil evidence of salamnders and frogs This is salamander Xrf analyss- look at composition of rock to look at what the structures and elemnts of the fossil are

Answer 183

Palaeobatrachus gigas from the Cretaceous of central Europe (Czech Republic), showing the distinctive urostyle that facilitates jumping in crown- group frogs. Eurostyle- fusion of vertebra to jump better- common in this time Best known group of lissamphibians Appeared sometime in Jurassic Key attribute- attributes for jumping- remodeling of pelvic girdle and sacral vertwebrae to jump better- salatory lifestle

Answer 184

Beelzebufo. This large frog had a skull about 20 cm wide, and could have generated a bite force of approximately 500 N. This is comparable to the force involved in a human bite, and would certainly have been sufficient for it to feed on small lizards and mammals, and possibly even on juvenile dinosaurs. Huge frog Eats little dinasours Madagascar- still attached to Africa at this time- was at higher latitude and climate semiarid and dry seasons with long periods of dryness then heavy rain Enormous head Eurostyle- in middle Lived like a toad- drier environment On head rough patches- osteoderms, armoured head- some look like horns Short limbs Interpret this as an attack animal- sturdy and aggressive Absence of a tympanum- hunting vertebraes, don’t need to hear high frequency sounds- prob eating smaller vertebraes

Answer 185

The Cretaceous witnessed rapid geophysical changes that resulted in major climatic fluctuations, so that global conditions were tropical at the beginning of the period and more temperate at the end The continents began to assume their modern configuration, but were flooded by seas that were as much as 300 m higher than today Oceanic Anoxic Events (OAEs) had a major effect on the Cretaceous marine environment, and may have led to the extinction of the ichthyosaurs, among other groups What trends might exist between the appearance of the Cretaceous Terrestrial Revolution and contemporaneous trends in vertebrate evolution? The Western Interior Seaway (WIS) appeared and became the largest shallow marine body of water ever to have existed on Earth, linking the Arctic to the Gulf of Mexico and having a moderating climatic effect that maintained warm, subtropical conditions at relatively high northern latitudes Galeomorph sharks diversified, with many modern clades appearing and distant relatives of the extant great white shark taking on an apex predator role,- was similar to today as skates and rays underwent their own diversification and shark populations began to assume their modern geographic distribution, foundation is set Sharks survived the end-Cretaceous mass extinction, but the largest Cretaceous forms disappeared at the Cretaceous-Palaeogene boundary Bony fish underwent a major adaptive radiation, with most major modern clades making their appearance by the Early Cretaceous Some bony fish evolved into large pelagic- open sea predators, which included the biggest predatory bony fish to have existed since the Devonian The three major extant lissamphibian clades became firmly established- gave us the modern groups

Answer 186

• Landforms resembling current continents began to appear • Although the climate was mostly tropical, periods of cooling and glaciation occurred, notably during the Late Cretaceous • Continental elevations were generally higher than at present • Sea levels were high, as much as 300 m above present ones • Evidence for Oceanic Anoxic Events (OAEs) • An extraterrestrial impact almost certainly had a major impact on vertebrate extinction at the end of the Cretaceous shark aversity Increased during the late cretaceou. • Bony fish underwent major adaptive radiations • Modern lissamphibian clades diversified • Modern mammalian clades appeared • Cretaceous Terrestrial Revolution (flowering plants evolved) • Dinosaurs underwent major adaptive radiations • Giant pterosaurs, some bigger than small aircraft, evolved • Crown-group crocodilians evolved • Plesiosaurs and turtles diversified • Western Interior Seaway provided an environment conducive to the evolution of the mosasaurs, which were the last major marine reptile groud to appear

Answer 187

Western sea- inland sea over north America- down to Utah Starting to look more like today Lots of continental upheaveal- elevation- Have more diversity because of this geographic situation Continents begin to take-on modern arrangement. Note how the general shapes of the present-day world can be easily recognized, albeit some such as India are in quite a different location.

Answer 188

Could the Cretaceous have experienced a similar climate to that which we experience today? If so, how is it that fossils of tropical fauna and flora could be found at high palaeolatitudes? More tame and stable, more consistent climate- helps evoloution Stlill much warmer- have tropic in higher latitude Subfreezing temps fpr several months causing exctinction- how are the animals surviving Extreme latitudes- have seasonal deepfreeze Updated models- more moderate north and south pole climate existed Thought was seasonal deepfreezes but taking into account topography and sea levels- not correct

Answer 189

Sea level changes suggest a more moderate northern and southern polar climate, falsifying the idea that taxa inhabiting high-latitude regions during the Cretaceous would have faced periods of extreme cold. The polar flora and fauna of the period would still have had to deal with extended periods of darkness, but these would have posed far less of a threat to survival than temperatures low enough to freeze biological tissues and cause severe cellular damage. Darkness- higher latitude, longer days and more dark periods Wasn’t as cold Temp- less threat to survival Temp drops for increasing elevation- drops 4-6 degrees

Answer 190

Areas of higher elevation are more prone to greater rates of erosion. A geologist can calculate the original altitude of a particular region by measuring the volume of sediments that have been deposited in an adjacent sedimentary basin. However, this method of reconstructing palaeotopography works well only if certain assumptions are met. What are these assumptions and what is the evidence?- sediments are ditridal- washed from nearby source, continents haven’t undergone deformation? Igenious and carbonisious rocks- not as accurate They dissolve in the sea water due to acidity- precipitate anywhere in world Sediments erode and end up in near by water- looking at sediment deposition rate can help understand how fast erosion is happening Have salt and dissolve in water- goes everywhere, spreads through the body of water Mountains- primarly carbinicerous rocks

Answer 191

Researchers have made an effort to more accurately estimate the palaeotopography of the Cretaceous by factoring in the expected redistribution of carbonates to lower latitudes and have compared the results with the topography of the modern world. Today, the average altitude of the Earth’s continental land areas is around 830 m above sea-level. This average is increased by what might best be described as modern outlier elevations, including Antarctica’s average elevation of 2250 m and the equally anomalous elevation of Asia’s Tibetan Plateau (4000 m above sea- level). What is a more reasonable estimated average of our current continental elevation? Increased elevations indicate a cooler climate Average estimate- 100 m higher elevation than today- so should be colder, but it wasn’t

Answer 192

For various epochs within the Cretaceous, researchers have determined that, ignoring extreme outliers, the average global elevation was 665 m during the Aptian, 515 m during the Cenomanian, and 525 m during the Maastrichtian. A l of these Cretaceous average values, of course, are at least 100 m or so higher than the average for the modern world if Asia and Antarctica are excluded. Would this greater elevation not suggest a cooler climate?

Answer 193

Could higher sea-level during the Cretaceous have moderated the climate of that time? Could higher sea-level have reduced the impact of elevation during the Cretaceous?- yes If sea-levels played a role, what is the evidence? Could higher sea-levels have actually reduced the average Cretaceous continental elevation? Take into account sea level- more water, more buffer to climatic swings No glaciers at this time- have higher sea level Higher sea levels reduce the impact of the elevation- 100-200 m higher than td Sea levels rose dramatically during lower cretaceous- so elevation decreases

Answer 194

In the modern world, cold arctic waters help to drive the circulation of ocean currents by establishing what is described as a conveyor belt. As the planet rotates the water at the poles cools and sinks, establishing a poleward flow at the surface and an equatorward flow at depth.- tward artic- shallow As the cold water sinks, it brings oxygen down to the lower layers of the oceans, keeping them well- oxygenated and hence capable of supporting a more diverse and more abundant biota. What were the conditions like during the Cretaceous?- not as strong as td, low topography relative to sea level- not as strong climate effect Tropical and appearance of savannahs and grass Gulf stream- reason why Europe is warm, and east coast is warm- warm current from equator Global ocean currents operate on temp gradients warm water rises goes to artic then sinks and. Goes back down- conveyor element Warm in shallow- go to artic, get recycled How the nutrients mix In cretaceous- not as strong temp gradiensts

Answer 195

Warmer waters during this time less capable of skinking, deep water becomes anoxic The modern world and the link between North and South America through the isthmus of Panama interrupts the westward flow of the Atlantic currents. This would not have occurred during the Cretaceous as the two continents were not connected. What might this have permitted? Prange- gulf stream- how nutrients and oxygen cycled through ocean

Answer 196

Evidence points to a cooling trend throughout the Maastrichtian. Used to tropical climate, then gets cooler- impacts the animals First years- inc temp, rising sea levels Some occasional drops- one coincide w middle- late cretaceous Last age- Maastrichtian- drops in global temp, ratios of oxygen and carbon let us know this Why- drop in sea level, reduction in co2 May have been driven by inc forest

Answer 197

Could the Bolide- extraterrestrial(meteor) Impact have been the primary cause or was the cooling trend described in the previous slide or extensive volcanism have been the primary culprits? Let’s examine the evidence.

Answer 198

66.1 million years ago a 10 km wide asteroid collides with the earth.- very big, causes casade effect, vaporizes around it, trigger volcanism, tsunami- nuclear winter, no sun, ash, cold All nutrient cycling stops and food webs shut down temporarily. Many marine animals and plants go immediately extinct. Terrestrial systems experienced catastrophic fires – forests disappear. Epic tsunamis inundate coastal and low-lying areas. Asteroid Impact Theory Helen Michel (far left) and Frank Asaro (middle) – geochemists. Walter Alvarez (standing) – geologist Luis Alvarez (far right) – physicist © Cambridge University Press 2016

Answer 199

Main indicator- A rare element (Iridium)- common in space rock is found in abundance at three locations (Gubbio in Italy, Denmark, and New Zealand) from around the world – all dated to the exact same time interval.- thin layer found all over earth The widespread distribution of this Iridium layer which was found in concentrations 30X that which is normally expected was part of the evidence used to calculate the size of the bollide (asteroid). The Iridium layer has since been found in many other locations as well as in ocean sediments.

Answer 200

The Iridium Signature • Known Iridium Locations Samples all over the world Gulf of mexico clay layer can be readily seen – location in Montana.

Answer 201

The Fort Union formation is part of the Cenozoic and no dinosaur remains present. The He l Creek Formation represents the last part of the Cretaceous and dinosaur fossils are abundant. Common formations in western North America

Answer 202

The Fort Union formation is part of the Cenozoic and no dinosaur remains present. The He l Creek Formation represents the last part of the Cretaceous and dinosaur fossils are abundant. Common formations in western North America

Answer 203

Shocked Quartz Note the striations in the quartz crystal. This implies exposure to sudden catastrophic heat as is found in regions that have been exposed to nuclear blasts or to asteroid impacts. Quartz- pretty sturdy, doesn’t break in this fashion naturally The striations caused by meteor, extremely strong force

Answer 204

Evidence of massive tsunami deposits throughout what is now the central regions of North America. The impact crater itself can be seen in the present-day Gulf of Mexico, which at the time of impact was the south-end of the Western Seaway that cut through North America. © Cambridge University Press 2016 Area during cretaceous Created tsunamis and destroy everything in this area

Answer 205

Note the crater in the centre of the reconstruction and the concentric rings around that centre. Note the oblique strike as shown by the blue and green extensions of impact ejecta leading to the upper left and right of ground zero. Present day Yucatan Peninsula in Northern Mexico. Hard to find the hole- in water

Answer 206

Could other events have contributed to the Cretaceous- Paleogene mass extinction? The Deccan traps in India. These lava traps are the result of extensive volcanism near the end of the Cretaceous. May have had some role Deccan traps- volcanic layers- massive events- siberrian traps Extensive volcanism during this time in india

Answer 207

declined to about 10% of what had the case prior to the impact. Based on ocean cores, limited productivity remained for 1.5 million years after the impact.- took life time to bounce back A l of these organisms went extinct Bio-productivity or the nutrient cycling that is essential for a healthy ocean

Answer 208

Leaf fossil Angiosperm- fleshly leafed plant0 still around today The leaf of a common angiosperm from the late Cretaceous that was native to North America. It became completely extinct at the K-T boundary. How could the elimination of plant species have impacted animal life?- collapse pf food web

Answer 209

Species survival graph from two independent sources. What does the survival graph suggest? Smaller species seem to be less effected Oceanic life- see more survival Anamniotes- hit hardest

Answer 210

The Cretaceous witnessed rapid geophysical changes that resulted in major climatic fluctuations, so that global conditions were tropical at the beginning of the period and more temperate at the end The continents began to assume their modern configuration, but were flooded by seas that were as much as 300 m higher than today Oceanic Anoxic Events (OAEs) had a major effect on the Cretaceous marine environment, and may have led to the extinction of the ichthyosaurs, among other groups What trends might exist between the appearance of the Cretaceous Terrestrial Revolution and contemporaneous trends in vertebrate evolution? The Western Interior Seaway (WIS) appeared and became the largest shallow marine body of water ever to have existed on Earth, linking the Arctic to the Gulf of Mexico and having a moderating climatic effect that maintained warm, subtropical conditions at relatively high northern latitudes

Answer 211

Devonian witnessed major climatic event that had detriemental effect on tetrapod, but some survived and continued to diversify amphibians, reptiles, bird and everything in between First tetrapod- colosteus emerging from basal tetrapods and relatives comes from fish with (limbs) Reduction of bones, evoloution of eating- led to tetrapods Debate- where amphibians came from is a major question- debate stems from temospondylii hard to distinguish between reptiles and amphibians Has word morph in it- designation for animals along stem to crown group- includes all descendants Many grey areas, some don’t fall into classification Lepospondly- sister to temnospondyl Many termed stemmed amniotes

Answer 212

Many of the largest tetrapods of the period were amphibians and on land they were the apex predators. Megalocephalus Note the absence of a large otic notch and the unusual keyhole shaped orbits. Amphibians top predators, ambush predators , not running- not pursuit predators Otic notch- associated with hearing- ear hole that supports membrane, not ossified On land have to adapt ways to hear, smell, eat Has small otic notch to hear

Answer 213

extensive lateral line system. Long bodied amphibian Has ridges and structures on skull, for sensory organs- usual for aquatic animals Reduced limbs, strong tail, swims around the swamp, more than 40 distinct vertebra between hips and neck, poorly ossified limbs

Answer 214

Note the exceptionally small forelimbs and the rather fishlike appearance of the life-reconstruction. • This taxon possessed a special type of dentine known as "dark dentine" or more formally named "petaloid" dentine. • What is the significance of this histology? Aquatic amphibian 4 limbed Don’t go straight into land- find niche or alternate Lay eggs in water or damp environment Initially thought to be derived from antropod lineage- bc of tooth morphology and had dark denting- histology- pelatoid dentive Dark dentint widespread in tetrapod- not a synapomorphy Greater diversity of tetrapod body plans

Answer 215

Temnospondyls and the evolution of the impedance matching middle ear (IMME). Monophylitic taxon- uncertain colosteus- grouped with members of this group Important for understanding evoloution of IMME- important- major adaptation for life on land Sound is vibration through air- IMME- has structures and a tempanic membrane can send the vibrations to the brain

Answer 216

They share the following derived characters: Large interpterygoid vacuities (open palate)- gap in top of mouth. These may have been used in breathing as part of a buccal pump (as in frogs). Get air into lungs by using mouth to force air into lungs Occipital condyles present- spinal cord attached to skull, notochord excluded from skull. The skull table-excludes palate and braincase is firmly sutured with the cheek. There was no mobility between the two units. There are only four digits in hand. Not much flexibility in head

Answer 217

Note the very large openings in the palate of the temnospondyl, Dendrerpeton. These large vacuities may have been important in temnospondyl respiration. Amphibians have flat heads Dominant predators on land at this time Empty space in palate- create pressures to force air down lungs and help them breathe on land – facilitates buccal inhalation, may help them swallow better- using eye contraction to swallow prey, providing space capable of accomadating jaw and may reduce force required to close jaw, allow greater control of jaw closing Dendrerpeton- upper pensylvannian time, tetrapod, fully formed hand and feet, terrestrial- lack head structures of aquatic animals Amphibians today very different from past amphibians

Answer 218

Why the need to hear better on land? Note that sound travels less efficiently in air than in water. Not as far or strong You need to hear if you want to catch prey or avoid being captured as prey. Important for mating- mating call What anatomical changes need to occur? Lateral-line system of fish no longer useful on land. Vibrations could be felt, but these are only low frequency sounds. Early amphibians can hear it To hear higher frequencies, you need an IMME. Greatly enhanced sensitivity of sound Evoloution essential made it possible foor early tetrapods to hear High density of water- interpret vibrations of water through body and jaws

Answer 219

Why the need to hear better on land? Note that sound travels less efficiently in air than in water. Not as far or strong You need to hear if you want to catch prey or avoid being captured as prey. Important for mating- mating call What anatomical changes need to occur? Lateral-line system of fish no longer useful on land. Vibrations could be felt, but these are only low frequency sounds. Early amphibians can hear it To hear higher frequencies, you need an IMME. Greatly enhanced sensitivity of sound Evoloution essential made it possible foor early tetrapods to hear High density of water- interpret vibrations of water through body and jaws

Answer 220

typical rhipidistian fish early temnospondyl Note how the hyomandibular is surreptitiously placed to conduct sound to the inner ear region. Does function in hearing- vibrating of it and jaw and skull stimulate cells in inner ear Imporved by javing reduced hyomanidibular- turned into IMME To adapt this echanism have to co-op mechanism for fish and change it for on land Stapes- sturdy and more of supporting element but in reptiles- used for hearing more Vibrating bones in head to transfer the sound to brain Gradient between inner and outer ear- middle ear can enhance vibrations from outer ear Functuonal IMME- requires moving stapes that is slender- has to be able to move to interact w other ear structures and enhance vibration- higher frequency

Answer 221

The tympanic middle ear of temnospondyls may have been useful to detect prey and predators on land, but it is also possible that temnospondyls emitted mating calls and that the they found their mates this way, like frogs today. This hypothesis is plausible, because frogs and perhaps all modern amphibians are thought to be derived from temnospondyls. This hypothesis is also supported by the great diversity of temnospondyls. The mating calls may have a been a good way for males to attract females of the same species. Temnospondyls- lots of them around, need to be able to hear own species and find them Amphibamis- basal most temnospondyl- stapes slinder enough to have IMME- must of needed this bc strong favor for it, among this taxon stapes wasn’t conserved structurally

Answer 222

A diverse group with a number of specialized anatomies Closer to reptiles Monophylitic group of amphibians

Answer 223

They are all relatively small. They all lack an otic notch. Lack labyrinthine infolding in the teeth- hoe dentine creates bridging along tooth The centrum – body of vertebra of lepospondyls is large and cylindrical. Usually have a single central element (at least in the presacral vertebra), although recently quite a few taxa have been discovered to have small presacral intercentra- smaller element between.

Answer 224

Very long bodies – aïstopods often have over 200 vertebrae. All lepospondyls have a single vertebral centrum. In aïstopods the neural arch is fused to the centrum. All aïstopods lack limbs and appear to have been semi- aquatic., could get very large Some nectrideans were long-bodied, but it was the tail that was long, and all had limbs. However, the limbs were poorly ossified suggesting that they were primarily aquatic. Limbless but terrestrial Similar to cisscilians

Answer 225

The Upper Carboniferous Tuditanus, which is almost a “dead- ringer” for the amniotes Paleothyris or Hylonomus. Lepospondyls- have lots of diversity- so are they directly below reptiles Small Microsaurs- diverse group some are terrestrial some are aquatic some have gills in adult life Three key characters in the debate: 1) Pedicellate teeth. In teeth of this type, the crown is separated from the root (pedicel) by a zone of fibrous tissue. 2) Cylindrical centra. This applies to taxa in which the vertebrae each have a single, cylinder-shaped centrum, rather than a separate pleurocentrum and intercentrum. 3) Bicuspid teeth. A bicuspid- peaks on tooth, which may also be pedicellate, is one that bears two distinct prominences (cusps).

Answer 226

There are 4 major groups of lepospondyls: Aïstopoda, Nectridea, Microsauria, and Lysorophidae. Together, lepospondyls have been regarded as sister-taxon to Amniota, as sister-taxon to Lissamphibia, or as sister-taxon to Caecilia, which would render Lissamphibia paraphyletic!

Answer 227

What is the primitive (plesiomorphic) condition? Is there homoplasy at play?-yes, independent convergance Cylinderical occues in some of these Wide spread \ancestral tetrapods have 2 parts Way that they come up with single cestrum happened differently

Answer 228

At the end of the Triassic, dinosaurs had gained a foothold and arguably had already take the first step to dominance. Was this dominance due to a superior physiology or simply a lucky one? Keep in mind that the end of the Triassic was punctuated by volcanism(large igneous province, central Atlantic, camp and experienced a very hot and dry climate. What possible advantage could these environmental changes have secured for the proliferation of dinosaurs in the Jurassic?- hot and dry, gave them ability to rise started in Triassic, in jurasic diversified more- prob due to Triassic mass exctinction- opened up niches

Answer 229

Major group of dinosaur, very diverse Earluesr- relatively small and bipedal- primitive condition of dinosaurs Eventually diversify into dinosaurs- stickosaurs- small bipedal taxa dissepear before end of Jurassic Neornithiscia- middle Jurassic Do well in start, some make it to the end but mostly replaced by neorithiscia- herbivoires- dental modifications

Answer 230

Major group of dinosaur, very diverse Earluesr- relatively small and bipedal- primitive condition of dinosaurs Eventually diversify into dinosaurs- stickosaurs- small bipedal taxa dissepear before end of Jurassic Neornithiscia- middle Jurassic Do well in start, some make it to the end but mostly replaced by neorithiscia- herbivoires- dental modifications

Answer 231

Heterodont condition of teeth- incisor teeth and then have molars Ornosthician Basal clade Small bipedal Forearms sahorter than hind arms, long tail- bipedalhands could grasp 3 distinct tooth types- incisor(front) canines, and molarphormes- molars in back In red- excavated region of dental, pocket of teeth- supporting fleshing cheeks- muscle for cheeks- help us chew Needed teeth and cheek muscles to chew the plants Function of large canines debated- intraspecific combat Appear in the Lower Jurassic and are recognized for their dramatic dental morphology, as the genus name implies. What function might that large caniniform tooth have served?

Answer 232

Two general patterns of masticatory movement, termed propalinal- back and forth of jaw, upper and lower molars move back and forth to grind food- patterns on , dental wear, striations and scratching arcilineal- vertical biting motion, up and down- need specific jaw moveements, only effecitive if mandible could rotate, quadrate must have been mobile, have been proposed. What are the differences in these two forms of mastication? In which direction does the evidence point?- lower jaw was capable of some movement, supporting arcilineal, ball and socket between dentry and pre dentry- can move relative to dentry- bottom jaw has predentry No consenus on chewing- evidence supports both but arcilineal is more supported

Answer 233

Fruitadens is a sma l (approximately 75 cm in total length) dinosaur from the Upper Jurassic (Tithonian) Morrison Formation near Fruita, Colorado is one of two known heterodontosaurids that were present in the latest Jurassic. Why might there have been a decline in heterodontosaurid species diversity?- no definitive answer, see more specialized organisms advance What is special about Tianyulong?- preserved soft tissue coat Late ornothisician Lower Jurassic Provide evidence for protofeathers- had a coating on their skins-Soft tissue fossils Ornothiscians become more specialized and herbivorous

Answer 234

The clade is diagnosed by three derived characters not present in basal ornithischians: 1- dermal armour, in the form of keeled osteoderms that form rows parallel to the midline of the body on the flanks and the dorsal surface of the body from the neck to the tail; 2- a well-developed postorbital process on the jugal- flaring cheek; and 3- a palpebral (supraorbital) bone.- bony eyelid Another clade Most armoured vertebra- cacolyps Dermal armour- ostifications of dermins, ontop or just beneasth skin, not part of skeleton

Answer 235

Early thyreophoran Ornothiscian- very large group Has a beak- lot of ornothiscians do Quadrapedal Trackways attributed tio this anima- can do both bipedal but primarily quadrupedal Relied on gut fermentation processes- no specialized teeth Big guts= need room to absorb nutrient from the plants Also rely on stones to break up the food Ranged in size from 1.5 metres to 4 metres. All had some armour in the form of dermal scutes or plates. The early Jurassic Scelidosaurus.- quite armoured Basal member of this clade Leaf like teeth- shearing and pulling of vegetation- soft

Answer 236

Life reconstruction of Huayangosaurus taibaii from the Middle Jurassic (Bathonian or Callovian Stage) of Huayang, China. Note the pairs of large spikes along the dorsal midline and the prominent spike above the shoulder and additional dermal scutes cover the flanks. This thyreophoran dinosaur was approximately 4.5 m in total length. Poor fossil record of this time period Spike= protection Therapods- apex predator Skull and leaf like teeth- relied on gut fermentation not mastication

Answer 237

The most derived Jurassic thyreophorans recognized by their fantastic plates and spiked tails. Stegosaurus was the most well known and best fossil representative of the clade. Ranged from the Kimmeridgian through the Tithonian. A mature in a Cypress swamp that was common during the Upper Jurassic. Most derived Plates on back- dermal osifications, well known fossil Largest of Jurassic thyreophorans Come from western north America

Answer 238

Sexually dimorphic Covered in keratin

Answer 239

Were stegosaurs bipedal or obligate quadrupeds? What can we deduce from bio-mechanical studies? What are the cha lenges associated with reconstruction posture in fossil taxa? How can we mitigate the uncertainty? Popular debate Posture in dinasoaurs- contentious Popular view- quadrupedal Had disproportionate limbs- fore limbs shorter= bipedal featyre How did hold its head- long neck- raised neck Head and neck can rotate- can look in any direction Head held in s shape May of balanced on tail One issue- limited fossil record- esp for cartiladge Bones attached by cartiladge Soft tissue- more important

Answer 240

Examined stegosaurs Top is traditional, slower and cant reach high vegetation, Bottom= probable posture

Answer 241

Isaberrysaura- oldest, may not be most basal and diet Collected in 2017 from deltaic sediments of Toarcian-Bajocian age from Patagonia (Argentina), the skeleton was incomplete, but included a nearly intact skull and much of the postcranium, including a substantial part of the trunk region with enclosed gut contents. What did these gut contents suggest?- seeds that are psycedelians Ate them, mutalism going on here, the seeds are poisionous- have something that neutralizes toxins- helped spread the seeds Later on neorthosicians- replased basal ones Asymetrrical tooth enanmel- greater on one side of teeth, keep teeth sharp Earliest= from middle jurasic

Answer 242

As Neornithischia evolved in the Jurassic two distinct clades appear. Marginocepahlians were not very diverse in the Jurassic but did include one important taxon - Yinlong downsi from the Upper Jurassic (Oxfordian) of the Junggar Basin, Xinjiang, China. What can you see in this skull that belies its taxonomic position?- typical serotopyian morphology, quadrupedal, large skull, herbivoire, no specialized dentine

Answer 243

Camptosaurus, Ca lovosaurus, and the dryosaurs Dryosaurus and Dysalotosaurus. All except for Ca lovosaurus, which is from the Middle Jurassic, are known from the Kimmeridgian and Tithonian stages of the Upper Jurassic. All of these taxa possess specialized tooth crowns that are shorter than wide, in addition to a joint that would have permitted the maxilla to rotate laterally as the lower jaw was closed. Kinetic articulation of skull- specialized chewing Cranial kinesis- specialized chewing, more dynamic chewing Sister tacon to margocinphelians

Answer 244

Camptosaurus and the thumb spike Perhaps the best-known Jurassic ornithopod and in possession of the thumb-spike that adorns the hands of members of this clade – the Ankylopollexia. What was the role of the thumb-spike? Reconstruction of Camptosaurus in bipedal pose - by Jack Wood. Basal ornothopod Very large Quadrapedal Preferred bideal though- different from derived seroptyiions Small skull, recessed teeth, fleshy cheeks- greater reliance on buccal methods Dital relative- psauropod Less bulky gut, more agile One non cranial aspect- thumb spike- important Not actually a thumb- loss of phalanges- in this digit- synapomorphy of thyroforms- tear bark, vegation, not definitive

Answer 245

Note the apparent radiation in the Upper Jurassic. Neotheropod synapomorphies: 1- astragalus and calcaneum fused; 2- astragalus with incipient anterior ascending process; 3- calcaneum mediolaterally compressed; 4- tibia bears prominent ridge on posteromedial surface; and 5- distal end of tibia bears distinct scar on anterior surface Undergo first radiation in Jurassic to middle Jurassic Become more astabloshedh- Coelophysis Coelurosauria- leads into birds Theropoda are birds Changes to ankle and its articulation at tibia

Answer 246

plung hape borneans • 1- asymmetric premaxillary teeth • 2- a strap-like scapula expanded fifac sledo. englasars/feasty reached • In addition to prominent nasal and supraorbital homs, it possessed very large maxillary teeth, which are sometimes described as "steak knives" given their serrated, strongly compressed and anteroposteriorly expanded morphology.slicing and dicing meat Notes Dilophosaurus- large therapod Praying on orthiscians Ceratosaurus-Relativeky primitive lacks derived features Ridges on head and above eyes- form grimentation Temnospondyl- have sculpturing, ridges on skull No other therapod has it

Answer 247

What is the evidence for the relationship between the tetanuran Allosaurus and the more primitive averostran Ceratosaurus? How do the sku ls shown here help develop the competition hypothesis? Skulls of theropods from the Upper Jurassic Morrison Formation, including the robust morph of Allosaurus (A) the gracile morph of Allosaurus (B), and Ceratosaurus (C). Orbit shaded in grey. Note the differences among the sku ls in length, width, and proportional maxi lary tooth size. Niche partitioning Teeth and theiur rile Taxa similar to each other in size- large predators, occupy same area and time- would it cause competition Two morpho types- same species allosauraus and ceratosauraus Difficult for them to exist unless have niche partitioning Robust= bulkly Gracile- elongated, narrow, fragile Gracile- looks like ceratosaurus- based on head shape, did they have competition? Length of skulls and teeth- discrepancy in tooth orimentation Ribust- , abundant posterior, capture and kill- smaller prey, crunching on prey gracile= verticle teeth, wider gape, slash and wait, wound prey and wait for animal to die upright teeth- can slash, effective against large and slow prey- ornothiscians Ceratosaurus- abundant animal, more of them= less gracile animals- competing Lack of coocurance of gracile and ceratosauraus

Answer 248

Diagnosed by three distinct synapomorphies, allosauraus: 1- reduction in the posterior extent of the dentition, less teeth in back of jaw, 2- large hands for manipulating prey, and 3- interlocking caudal vertebrae, resulting in a stiffened tail- helped them pivot faster. What might the interlocking caudal vertebrae be useful for? Earliest tetanurans are from the Middle Jurassic in the form of Megalosaurus. The most derived members of the clade include the iconic Allosaurus. Appear that gracile- may be better- may be bc of dtiffened tail- agile, pivot and run fast, allowed them to pivot on feet faster Agility= slash and quick retreat

Answer 249

Note the nearly vertical orientation of the teeth in the fossil cast of Allosaurus. What is the advantage of having this nearly vertical arrangement?- slicing rather than gripping, long jaw, wide gape, feed on lots of different prey Most famous dinasour- one of Steak knife dentition Teeth orientation- verticle- Certasoauraus- couldn’t hunt small prey as well

Answer 250

Used for prey Helped them be more agile Hand was robust- 3 digits, curved claw first digit=larger Narrow claq Tubercule- bulge- attachement of the tendons be able to grip

Answer 251

Avetheropods may be distinguished from basal tetanurans on the basis of three synapomorphies: 1- presence of a maxillary fenestra- most important bound by maxilla, 2- significant reduction or complete loss of manual digit IV, and 3- extensive pneumatization- air pockets, reduce body weigjt of the vertebrae Allosaurus, while not an avetheropod, was clearly on the avetheropod stem and while retaining prominent a hands a trait that was later lost in advanced avetheropods, Allosaurus was able to dispatch different sources of prey and would not have been tied to large prey as was the case for the more primitive Ceratosaurus.

Answer 252

The most advanced Jurassic theropods and the clade that would give rise of Tyrannosaurus. Coelurosaurs are derived relative to other Avetheropoda in having the following characters: 1- increased brain size, 2- hands with long and powerful fingers, 3- exceptionally slender and stiff distal portion of the tail, 4- long and slender metatarsals producing a bird-like foot, and 5- simple filamentous feathers.

Answer 253

The earliest and most basal member of the Coelurosauria is the genus Proceratosaurus from the Bathonian Stage of the Middle Jurassic of England. Younger relatives such as Ornitholestes and Coelurus, from the Upper Jurassic Morrison Formation of Colorado, specialized on prey that was too sma l to attract the attention of the larger and more primitive ceratosaurs and allosaurids. This difference in prey selection would have served what purpose?- niche partitioning, trying not to compete Ironic that these sma l Jurassic theropods would ultimately give rise to the largest ever!

Answer 254

Compsognathus emerged during the Tithonian Age at the end of the Jurassic and represents one of the smallest known non-avian theropods at approximately 1 m in maximum adult length. This taxon would have been very agile and undoubtedly also quick, and probably fed on non-dinosaurian prey including small reptiles and possibly even mammals.

Answer 255

Derived relative to more basal coelurosaurs by possessing: 1- enlargement of the brain, even relative to other coelurosaurs, 2- an elongate forelimb, 3- a large and well-ossified sternum, and 4- a highly convex semilunate carpal in the wrist. What serendipitous function could this special wrist bone come to serve- allow movement Another group, closer to birds Birds nested in this clade Derived forlimb traits- evolve bird like wing Little feathers Pectoral muscles

Answer 256

Yi attracted attention because of the simultaneous presence of feathers and an unusual flight membrane, which superficially appeared to represent an unusual combination of pterosaur and bird characteristics. Yi was heavily covered in feathers. The plumage extended “from head to toe”. The feathers varied in appearance The head and neck sported stiff, filamentous feathers ranging in length from 15 to 20 mm. The body was covered with larger feathers, ranging up to 60 mm in length, which even extended to the metatarsal region of the hindlimb (i.e. the ankle). The forelimb bore feathers measuring from 35 to 60 mm. Feathers and membraneous wing, stem bird Experamentation along the way to birds Glider rather than flyer Equivalent structure of terapoid- tera Extends from wrist to support wing Elongated digit

Answer 257

The first Archaeopteryx feather was reported approximately two years after Darwin’s publication of On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life, on November 24th, 1859 . The first articulated skeleton, now known as the “London” specimen, shortly followed. The specimen was found in Germany and not in London and in the vicinity of Solnhofen, Germany (Bavaria) and came from the same limestones as Pterodactylus and Rhamphorhynchus. Intermediate between dinasours and birds First bird like organism While quite complete, the cranial anatomy of Archaeopteryx would remain unknown until the discovery in 1874 of the nearly complete “Berlin” specimen, which included a virtually intact skull.

Answer 258

Filamentous structures Emmerged sperate times along arthosauria Only feathers in derived therapods Filamentous feathers- basal therapods Large variety of filamanteous feathers among archosauria The study of the structure of filamentous feathers, particularly in Middle and Upper Jurassic theropods, has benefited from the some superbly preserved fossils of feathered taxa from Chinese Lagerstätten dating to around 160 million years ago including: Yi, Ambopteryx, and Epidexipteryx. The filamentous feathers preserved in these non-avian theropods are essentially hollow, tubular structures, resembling early developmental stages in the feathers of extant birds. A modern feather initially forms as a cylindrical sheath that emerges from an integumentary pit known as a feather follicle and as a tubular, hollow structure, on which appear ridges that will subsequently develop into the barbs of the adult feather. Barbs are branches that extend away from the rachis (central shaft) of the feather, which possess additional branches known as barbules that in turn may or may not contain small hooks (barbicels). If the small hooks are present, then the feather is rigid, and resembles the prototypical outer feather that we see in birds, but if the hooks are absent then the feather is fluffy (i.e. the down feather coat that serves in an insulatory capacity). The filamentous feathers seen in many theropod taxa effectively reached the hollow tubular stage, but went on to mature without ever undergoing the additional developmental step of barb ridge formation Were feathers primitive for dinosaurs or did they evolve inpdendently in Ornithischia and Saursichia?- independent or they are lost in sauropodomorphs

Answer 259

Two apparent radiations occur in the Jurassic What might the reason for this be? Does the Jurassic climate gives us any hints?

Answer 260

A basal sauropodomorph that replaces the Triassic Plateosaurus. Why is this taxon so critical to understanding sauropodomorph behaviour and physiology? Massospondylus is less notable for any osteological feature than for its sheer abundance, and particularly for the fact that the specimens of this genus collected in recent decades include a clutch of eggs containing spectacular fossilized embryos. The embryonic remains depict a quadrupedal posture, but the adults are undoubtedly bipedal! What does this finding suggest and how does it help to more fully understand the evolution of later sauropodomorphs? Perhaps the most startling feature of the Massospondylus embryos, especially considering that they were probably close to the hatching stage, was the absence of erupted teeth. If hatchlings were toothless or nearly so, their parents may have had to provide them with some sort of easily processed food in order to ensure their survival. The relatively poor ossification of the limb girdles of the Massospondylus suggests limited ambulatory capacity, another indication that elaborate parental care may have been needed.

Answer 261

The only known material of Vulcanodon was recovered from southern Africa, specifically what is now Zimbabwe. At an estimated length of up to 11 m, Vulcanodon may have been about twice as long as Massospondylus, but was certainly nowhere near as large as many of the sauropods that evolved later in the Jurassic.

Answer 262

The evolution of the sauropods throughout the Jurassic was a story of emerging gigantism, as some of the biggest vertebrates to ever walk the Earth evolved and came to dominate what remained of the period. Predators, in turn, responded by evolving strategies for targeting the ever- larger behemoths that were now prevalent in terrestrial environments. How confident are we regrading the gigantism trend? Could this apparent relationship between predator and prey be simply coincidental?

Answer 263

Ornithischians diversified - what does the fossil record tell us about their evolutionary history? Specialized dentition and the evolution of a masticatory apparatus - did all dinosaurs have fleshy cheeks? • The evidence for, and function of, filamentous, dermal integumentary structures in ornithischians - are feathers primitive for Dinosauria • What function might the bony plates of stegosaurs have served? • How did some theropods specialize on a specific feeding behaviour? Isabenysaura mollensis and the first evidence for mutualism between a plant and a vertebrate What evidence suggests that niche partitioning may have been an important phenomenon in Jurassic theropods snakil and the trent the age awont or foing on ang fay- stach and wal" ad capture What is the most unusual fact about the Upper Jurassic theropod Yiqi? What features indicate that the dinosaur Archaeopteryx is a bird? What is the logic behind the statem at all birds are dinosaurs, but not all dinosaurs are birds? If birds are dinosaurs, can we continue regard Reptilia as a monophyletic group? Did feathers evolve for flight? What evidence might help answer this question? Is it true that early sauropodomorphs were bipedal rather than quadrupedal? What aspects of dinosaur behaviour has the discovery of Massospondylus embryos forced us to revisit? Hint - babies need care! The role of the sauropod neck in feeding, the link between an enlarged neck and quadrupedality, and the mplications of Centre of Mass position for body posture

Answer 264

Ichthyosaurus and Leptonectes, what do they have in common?- smaller After surviving the end-Triassic extinction, they eventually become extinct in the Lower Jurassic – Why? What does the geological, climatological/environmental evidence suggest? Are there similar events that have occurred after previous mass extinctions?

Answer 265

What are they?- population killed off, only few organisms reproduce What are the consequences?- less variety Can we make a case for a similar explanation when looking at ichthyosaurs? Consider the evidence – how confident are we in our interpretation of that evidence?

Answer 266

What does this figure illustrate? A – Morphological disparity B – Morph. Disparity (RED) vs. Taxic diversity (BLUE) How confident are we in some of its inherent conclusions? Pay attention to the BLUE plot in each graph. What do you see? What does the body shape imply?- open ocean swimming How is this taxon different from the Lower Jurassic Ichthyosaurus? Hint – trick question! Are their limits to the body form? Adaptations for Speed

Answer 267

Straight= reduce drag Straight= reduce drag

Answer 268

Is the skin histology informative when assessing swimming capacity? What does it mean to possess a dermis with a cross-fibre architecture?- resist stress, return to original position Examine this cross-section through garden hose designed to resist kinking. What do you see?

Answer 269

Think back to the cladogram for ichthyosaurs and consider how this cladogram differs. What conclusions can be made?

Answer 270

Nothosauridae (exclusively Triassic). Pachypleurosauridae (exclusively Triassic). Nothosauridae (exclusively Triassic). Pachypleurosauridae (exclusively Triassic). Plesiosauria (Triassic, Jurassic, and into the Cretaceous).

Answer 271

Plesiosauria- small heas long neck propulsion - tail driven Pachypleurosauridae propulsion - limb and tail driven Nothosauridae- near-shore habitats lagoonal to shallow coastline habitats propulsion - exclusively limb driven Pistosaurus predominantly Plesiosauria open-water marine habitats tendency to hyperphalangy and a decrease in tail length coupled with stiffening of torso

Answer 272

Plesiosauroids have relatively long necks and small skulls and their fore- paddles are equal of longer than their hind-paddles. Pliosauroids have relatively short neck and large skulls and their fore-paddles being shorter than their hind-paddles. Are these anatomies phylogenetically relevant within Plesiosauria? Whether pliosaur or plesiosaur, the need to stiffen the torso and develop an effective propulsion system was essential in both groups. Note the very heavily ossified underbelly of a typical plesiosaur and the compressed phalanges in the Upper Jurassic plesiosaur below. All plesiosaurs are best interpreted as aquatic fliers (e.g., sea-turtles or penguins). Their mode of locomotion is energy efficient and provided plesiosaurs with the capacity to traverse deeper, pelagic marine environments. Could this efficiency in swimming have minimized the threat of extinction? If so, how?

Answer 273

During the earlier part of the Jurassic, this region was largely inundated by shallow seas, although there were many sizeable islands. As a result, there existed vast areas of suitable habitat for fish-eating aquatic amniotes such as plesiosaurs. Rhomaleosaurus was among the predators that took advantage of these conditions. Although not enormous at a maximum length of around 7 m, it would certainly have been the largest coastal predator of its time.

Answer 274

Competing morphology-based (A) and total evidence (B) phylogenies of Testudines (red circle) and their close outgroups, showing selected extinct and extant turtles. The total evidence phylogeny is based on a combination of molecular and morphological data and shows Pleurodira (in blue) nested within Cryptodira as sister-clade to Trionychia (in red). This arrangement renders Cryptodira paraphyletic. A global phylogeny of turtles reveals a burst of climate- associated diversification on continental margins

Answer 275

The Squamata (i.e. everything closer to modern squamates than to rhynchocephalians) are thought to have appeared during the Triassic (e.g., Megachirella wachtleri), if it is ultimately shown to be a true squamate. Why are squamates so difficult to find in the fossil record? Can we come up with some testable hypotheses for the paucity of the fossil record when it comes to squamates?

Answer 276

Diagnosed by a suite of synapomorphies, including: 1- cranial kinesis, involving mobility of multiple skull elements including the quadrate 2- paired hemipenes; 3- pleurodont dentition; 4- absence of gastralia; 5- double-hooked fifth metatarsal; and 6- an elaborate type of mesotarsal joint. Comparison of traditional, morphology-based phylogeny of crown-group Squamata (A) with modern, molecular-based phylogeny (B). Note the contrasting positions for Iguania and Serpentes.

Answer 277

The snake discoveries that have elicited such interest include four new species from the UK, Portugal and the USA, namely Parviraptor estesi, Diablophis gilmorei, Eophis underwoodi and Portugalophis lignites. • Analysis of snake origins concluded, based on the Cretaceous snake Coniophis precedens, that the snake body evolved prior to the snake head. • How do the new finds mentioned here challenge this view? • Why is it so difficult to track down the origin of snakes? "An important argument that has been put forward in connection with the four new snakes is that modern lizard groups are diagnosed primarily not on the basis of their general body shape and whether they possess long legs, short legs or no legs, but on the basis of their cranial anatomy. Why, then, should snakes not be expected to differ from other squamate groups primarily in their skull anatomy as well? It is important to keep in mind that body and limb proportions can be quite labile in squamates, and that| snakes are not the only elongate, limbless group."

Answer 278

How was Ichthyosaur diversity during the Jurassic impacted by the arrival of plesiosaurs? • Contrasting patterns of change in morphological disparity and taxonomic diversity among Triassic-Jurassic ichthyosaurs • The distinction between caringiform and thunniform swimming) • What is the functional significance of the cross-fibre architecture of ichthyosaur skin, and how does the presence of this architecture support the inference that Late Jurassic ichthyosaurs were fast-swimming predators? • As plesiosaurs diversified into a number of forms during the Jurassic, what was the basis for their success as pelagic predators? • Two basic plesiosaur morphotypes exist - distinguish between them and indicate how they relate to one another phylogenetically if possible • How might the Jurassic geography of what is today western Europe have influenced the evolution of plesiosaurs and other marine vertebrates? • What controversies currently exist with respect to the origination time and phylogenetic interrelationships of crown-group turtles, and what is their basis? • Squamates diversified during the Jurassic, but one taxon — the snakes — has proven enigmatic with respect to its evolution during this period • What is the advantage of using molecular data in combination with morphological data to explore the evolution of various clades? • How does the controversy over the phylogenetic position of Iguania affect our understanding of squamate evolution, and more specifically the origin of snakes?

Answer 279

Tropical World and the Age of Dinosaurs. The diversification of Sauropterygia continued, with the emergence of two distinct plesiosaur morphotypes. • Thunniform ichthyosaurs evolved. • Among dinosaurs, the Sauropoda evolved and the theropods gave rise to birds. • Pterosaurs diversified, and pterodactyloids appeared. • Modern mammalian clades appeared. • Squamata radiated and snakes evolved. • Modern turtle clades evolved. • The Lissamphibia appeared, and adaptations for jumping evolved among frogs for the first time. • Neoteleostei evolved, sharks diversified, and the first large filter feeding fish appeared. • The climate became wet, and atmospheric 02 levels increased. • Pangaea broke apart.

Answer 280

The end-Triassic extinction saw the demise of the crurotarsan terrestrial apex predators. In the Early and Middle Triassic, there were additional smaller scale extinctions. Volcanism is likely to have played a role in these smaller-scale events. Oxygen levels increase throughout the Jurassic peeking at approximately 27%, a trend that continued into the Cretaceous. Note the increasing distribution of recognized vertebrate families.

Answer 281

The end-Triassic extinction saw the demise of the crurotarsan terrestrial apex predators. In the Early and Middle Triassic, there were additional smaller scale extinctions. Volcanism is likely to have played a role in these smaller-scale events. Oxygen levels increase throughout the Jurassic peeking at approximately 27%, a trend that continued into the Cretaceous. Note the increasing distribution of recognized vertebrate families.

Answer 282

Excessive volcanism is evidenced by the LIP that dates to the latest Pliensbachian and across the transition to the Toarcian, about 183 mya. These extensive volcanic events impacted both terrestrial and marine environments, resulting in severe anoxic events that likely influenced the evolution of marine vertebrates. The out-gassing that resulted from these LIPs, increased the atmospheric concentration of CO2. However, unlike the trend in the Triassic, CO2 levels were balanced by Carbon burial and atmospheric CO2 remained stable.

Answer 283

As atmospheric CO2 concentrations increase, the green-house effect warms the earth including the oceans. Warmer waters hold less oxygen as oxygen solubility in water is dependent on temperature. Warmer ambient temperatures also increase the occurrence of more severe weather. More severe weather increases erosion which continues to feed sediment and its organic detritus to the ocean basins, which in turn further exacerbate the anoxic conditions that prevailed during the Pliensbachian and Toarcian. What consequences may result? The buried organic carbon is not accessible to the atmosphere and is unable to check the increasing concentration of atmospheric oxygen, which in turn results in increased phytoplankton activity. As phytoplankton activity continues to increase, O2 levels rise unchecked and the risk of forest fires, as had been the case during the Carboniferous, returns. Evidence is found in fossil charcoal in the early Toarcian. This trend persisted for about 2 million years. After this period, the ocean anoxia seems to abate. Why? During the Jurassic, the climate was somewhat wetter, and therefore considerably less harsh, than in the Late Permian and particularly in the even drier Triassic. It is likely that the wet conditions that prevailed during the Jurassic limited the occurrence of expansive wildfires, even though atmospheric oxygen levels were increasing. The humid conditions appear to have helped mitigate the fire risk.

Answer 284

Pangea breaks-up Note how Gondwana (large land mass bottom centre), which includes the resent- day continents of S.America, Africa, India, Antarctica, and Australia begins to separate from Laurasia (top left), which includes N.America, Europe, and Asia. What would this separation or break-up of Pangea have contributed to?

Answer 285

The oceanic anoxia events (OAEs) impacted life in the seas and sharsk and bony fish were hit hard. Among sharks, the end-Triassic extinction eliminated the Xenacanthiformes and the Ctenacanthiformes, and struck a major blow to the primitive holocephalians. The Galeomorphii, which includes most modern sharks take advantage. Hybodontiformes, which first appeared during the Carboniferous and underwent a modest radiation across the Triassic-Jurassic boundary decline toward the end of the Jurassic, eventually becoming extinct during the Cretaceous.

Answer 286

Paraorthacodus sp. from Eichstätt, Germany. Note the fin and body outline, and the prominent heterocercal tail so typical of most sharks.

Answer 287

They appear to have been more diverse than sharks during the Jurassic. Some forms even became adapted as giant plankton feeders, a role that is paradoxically filled by sharks and rays in the modern biota.

Answer 288

Adapted to living along coastal waters and continue today as tarpons and ladyfishes, which are common sport fish. These fish tend to be silvery in colour. They also have a swim-bladder that functions partly like a lung with some species needing to gulp atmospheric air in order to ensure full oxygenation. What conditions during the Jurassic might have selected for this ability? Hint – volcanism!

Answer 289

Appear in the Late Jurassic. As the name suggests these fish possess a bony tongue-like structure. Some osteoglossomorphs were quite large and would have served top predator roles. Many were well-adapted to fresh-water systems and remain as formidable predators even today (e.g., the south American Arapaima gigas).

Answer 290

A snake-like amphibian and how it sheds light on the origins of Lissamphibia. What is the relevance of Chinlestegophis? How does its phylogenetic position (previous slide) and the Jurassic taxon Eocaecilia help us to understand the origin of Lissamphibia?

Answer 291

Researchers have often argued for a separate origin for Caecilia, usually from microsaurs, whereas frogs and salamanders would have evolved from temnospondyls. While the temnospondyl origin for frogs and salamanders is generally accepted, the origin of Caecilia is less well understood. The finding of Chinlestegophis suggests that Caecilia are nested within Temnospondyls but arose from a separate stock. What is this separate stock and how supportive is the evidence?

Answer 292

As we discussed when exploring the Triassic, stem frogs can trace their origins to the Triassic and as members of the Temnospodyli, their parentage can be traced all the way back to the Carboniferous.

Answer 293

An early Jurassic jumper! Early Triassic frogs such as Triadobatrachus lacked a urostyle. What does the absence of a urostyle imply?

Answer 294

Jurassic salamanders and paedomorphosis. What is the basis for the argument exploring the evolutionary significance of secondary osteons?

Answer 295

A trend of increasing oxygen concentration from the Middle Jurassic into the Cretaceous is apparent in the marine rock record At least two carbon cycle perturbations are known to have occurred, one across the Pliensbachian –Toarcian transition and one later in the Toarcian Jurassic fires - fossil charcoal deposits of Toarcian age Galeomorph sharks diversified during the Middle Jurassic The first large filter-feeding fish, the actinopterygian Leedsichthys problematicus, evolved Innovations in the form and function of the swim bladder led to a radiation of bony fish The origins of the modern lissamphibian clades remain controversial, and stereospondyls may yet shed light on the origin of Caecilia Prosalirus bitis, an Early Jurassic frog, is the oldest known anuran to exhibit direct evidence of adaptations to facilitate jumping The early salamander Kokartus honorarius, and its implications for the phylogenetic relevance of secondary osteons What role did neoteny play in the evolution of salamanders? What fossil evidence is available, and how does this evidence help resolve the evolutionary debate?

Answer 296

Two clades are recognized and can be distinguished on the basis of ankle morphology. Crurotarsi- mobility concentrates at yelloe and calcaneum- 5th metatarsal is hooked Avemetatarsalia- fully optimized for rotational speed, metatarsal and tarsal more connected Can be distinguished based on ankle bones Metatarsal- fifth one is no longer hooked and reduced in size as is the first Cruotarsi- stand up on 2 legs or sprayed out like crocodile Joint cant resist bending Joint relied on musculoskeletal structure, so can withstand the stress on joints How did we come up with the two groups- do morphorlogical analysis- cluster similar traits and connect to phylogenetic interpretations Avametatarsalina- dominate more in Triassic- relitavely small- have one large organsism that makes it through the triassic

Answer 297

Crurotarsi- all living crocidiles- surviving group is modern crocodile- more successful in Triassic, less diverse Avemetartsalia- all living birds and non avian dinosaurs These groups don’t directly compete

Answer 298

Most well-known members of this clade include some forms that were very crocodile-like but are not related. These are best represented by the aquatic phytosaurs. Note the similarity in the skull between the phytosaur (top) and an extant salt-water crocodile (bottom) Can you pick out on major difference?- crocodilian has no antorbital fenestra- have solid bone Most well-known members of this clade include some forms that were very crocodile-like but are not related. These are best represented by the aquatic phytosaurs. Note the similarity in the skull between the phytosaur (top) and an extant salt-water crocodile (bottom) Can you pick out on major difference?- crocodilian has no antorbital fenestra- have solid bone

Answer 299

Early relatives of crodilians Diverse clade- some prob omnivores Had teeth adaptations for herbvore Armour along back Divereged from other curostarian in skull- gracile, large external naris- for smelling Sma l possibly omnivorous or even herbivorous crurotarsans. Comparison of the sku ls of the basal aetosaur Aetosaurus and the more derived aetosaur Stagonolepis. Reconstructions partly based on Desoto & Vizcaíno (2009).

Answer 300

By the Late Triassic, some crurotarsans such as Postosuchus were large hypercarnivores that had the apex predator role. Crurotarsans- carnivores Could run on land Thought to walk on 4 legs but its actually bipedal Prob paraphyltic Smaller one- gracile, quite fast, distinct from large organisms

Answer 301

The Avemetatarsalia represent the most derived members of the Archosauria. Avemetatarsalia They include what is the most successful major group of living tetrapod vertebrates in terms of species diversity - the birds. There are approximately 10,000 species of birds living today, nearly double the roughly 5,500 species of mammals. Smaller seem to do better during mass exctinction Was bipedal Why are they so small? Triassic avemetatarsalians were sma l compared to the contemporary crurotarsans

Answer 302

Comparison of hip joint structure between the crurotarsan archosaur Postosuchus (top) and an avemetatarsalian archosaur such as Lagerpeton (bottom), in left lateral (images on left) and anterior (images on right) views. Femur is straight- dislocation prevented by acetabular buttress- projected laterally from cetebelum- had shelf to protect from dislocating Groups differentiate by locomotion Upright- stabilized by femoral head- fit into cetebellum, femur articulates with head

Answer 303

Shortly after the appearance of Scleromochlus, avemetatarsalians diverged into two distinct clades, the Pterosauria and the Dinosauriformes. The early pterosaur Eudimorphodon- primitive. Note the long tail and prominent teeth. Can fly Fourth digit on hand is elongated to support flight Has pteroid- allowed membrane to extend from wrist to shoulder Terosaurs not dinasours

Answer 304

Last major archelosaur clade Paretical hypothesis*- unlike traditional phylogeny The dinosauriform taxon Silesaurus. Saurischia- plaves theroposda with ornithiscia so saurischian is reduced Early dinasour Stem dinosaur Shared prescense of mesotarsal ankle joint Beak like tip- cracked dense vegetation Herbivore Prob bipedal

Answer 305

Left femur (in anterior, lateral and posterior views, from left to right) and left pes (in anterior and proximal views) of Silesaurus. Note the prominent anterior and fourth trochanters, and also the expanded midshaft of metatarsal III, an adaptation to stiffen the foot for improved cursorial ability. As in many dinosaurs, the first and fifth pedal digits are reduced. How we differentiate them- based on feet Has trochanter shelf as well More primitive- pleasomorphic- gap is lost and head of femur is less in turned

Answer 306

Once we see dinosaurs they have a l the diagnostic characteristics regardless of the phylogenetic details. Recal the earlier alternative hypotheses of relationships (cladogram) a few slides ago, what differences to see here? Saurishcia- Two hypothesis if ornithiscia is sister to sarischia or sister to therapoda New phylogeny- redefine saurischian without therapods Within dinosauria- hard to distinguish between How do they regulate body temp Homeothermy- capacity to regukate internal temp metabolically, maintain temp, endothermy Heterothermy- body temp varies Gigantothermy- bulk endothermy- maintain elevated body temp bc of large size, water on body keeps warm

Answer 307

The basal sauropodomorph Panphagia. Note the relatively slender hindlimbs, which are more typical of theropods than of later sauropodomorphs. At barely 1.5 metres in total length, this taxon is also atypica ly sma l, even in comparison to the Norian-Rhaetian basal sauropodomorph Plateosaurus Shorter arms, bioped, slender head Could Panphagia have been carnivorous or at least omnivorous? What do these teeth suggest? Note the prominent carinae (cutting edges) on the labial and lingual surfaces, which would have been suitable for slicing through animal tissue. Herbivore but looks like therapod- where do therapods sit Eated fleshy vegetation Walks on two legs, gracile skull, long backlegs

Answer 308

Herbivore Bipedal Started in nest as got out of nest- started being bipedal Saupodorph While thus far, the two examples are reconstructed as bi-peds and the evidence strongly supports that posture, one sauropodomorph during the Upper Triassic was much more likely a quadruped – Riojasaurus. Why evolve quadrupedality? Pillar shaped foot- support excessive bulk Why become quadrapedile- may of retained juvenile conditions- pademorphisis

Answer 309

Basically walk on 3 toes • The early theropod Herrerasaurus from present-day Argentina. • Note the grasping hands and the long, narrow skull and jaws, all typical features of theropods. • Herrerasaurus retains five hindlimb digits, unlike more derived members of the clade, but digits I and V are much reduced and would not have touched the ground. The central digit (III) is the largest.

Answer 310

A sma l (about the size of a sma l dog) bipedal carnivore of the Late Triassic. Note the slender build, and the long hindlimbs and grasping hands that are the ha lmark of Triassic dinosaurs. Derived relative to Herrerasaurus in sharing the following synapomorphies with Neotheropoda: 1- premaxillary process thin and bar-like; 2- anteroposterior groove runs below, and parallel to, dentary tooth row; 3- splenial foramen present; 4- clavicles fused into a single furcula; 5- fifth manual digit absent; 6- manual digit IV with only one phalanx; 7- ilium with prominent ridge; 8- ischiadic peduncle distally expanded into “boot”; 9-pedal digits I and V significantly reduced in length; and 10- postcranial skeleton significantly pneumatized.- vertebral column has empty space Eodromaeus is higher up on the Theropod stem than Herrerasaurus

Answer 311

Early therapod- classic carnivore Predator Therapods filled ecological void of predator Jaw could snap close quickly Eyes had binocular vision- not obstructed, inc depth percedption Long tail

Answer 312

Triassic forms were rare but already distinctive. Pisanosaurus was sma l (1 metre in total body length), bipedal and possibly feathered. The dentition is clearly adapted for herbivory. Dominate in credacious Bipedal, long tail, long back legs Dentition- herbivore, grinding surfaces Crurotarsans and avemetarsalians were common and probably filled diverse niches.- bipedal, agile, running By the Jurassic these niches would be become ever more specialized. The Triassic also included some other major vertebrate groups, which will be examined in the next lecture.

Answer 313

Lepidosauromorpha and Archosauromorpha had diverged from one another by the Early Triassic, and the two clades went on to undergo extensive adaptive radiations by the Middle Triassic. Archosauromorpha gave rise to the Crurotarsi and the Avemetatarsalia, clades that differ in their ankle morphology. The Crurotarsi were dominant throughout the Middle Triassic. Bipedalism became predominant among the Avemetatarsalia, and evolved in a few members of the Crurotarsi as well. Avemetatarsalia diversified into a number of clades, including the Pterosauria and the Dinosauria. Both appeared in the Late Triassic, and avemetatarsalians came to predominate ecologically over crurotarsans. Both major archosaur clades experimented with a number of specialized niches, giving rise to aquatic predators such as the crurotarsan phytosaurs and terrestrial herbivorous forms such as basal sauropodomorphs and aetosaurs. The avemetatarsalians also experimented with flight with flight, in the case of the pterosaurs.

Answer 314

Main group are the ichthyosaurs or “fish-lizards” Also includes some enigmatic forms whose affinities have been debated. Most frequently regarded as the sister clade to the clade comprised of [Sauropterygia + Lepidosauromorpha] + Archosauromorpha. Adapted to living in ocean

Answer 315

Main group are the ichthyosaurs or “fish-lizards” Also includes some enigmatic forms whose affinities have been debated. Most frequently regarded as the sister clade to the clade comprised of [Sauropterygia + Lepidosauromorpha] + Archosauromorpha. Adapted to living in ocean

Answer 316

While many studies have pointed to Hupehsuchus as a stem ihcthyopetrygian, others are not so certain and a link to archosauromorphs has gained some supporters. Could ichthyopterygians be an archosauromorph Earliest possible ihcthyopetrygian Long toothless snout Limbs not true flippers Heavy dorsal armour- reminiscent of crocidiles

Answer 317

First well supported ichthyopterygian fossils are from the Olenekian and point to a rapid radiation shortly after the end-Permian extinction. May be own group of diaspida The long-bodied Grippia is the best know example of the ichthyopterygian branch. Note the absence of a dorsal fin and the asymmetry of the tail!- hypercircle, ventral lobe of tail expanded, aids in balance Push head down while swimming, keeping it level No dorsal fin May be sister to basal thersorians Articulation between sacrum and illium reduced- hind imbs not used to support body on land- fully aquatic

Answer 318

Tail ressembles lower Jurassic organisms Phalanges in flipper increased- hyperphallangial Inc elaborate as move up animal clade, more ones makes flippers more secure Mixosaurus was still rather primitive in its general body outline, but its front flippers were much larger than the hind flippers. Why might this anatomical difference been significant?- more control, maneuver in water True ichthyosaur Small dorsal fin

Answer 319

Large orbits Single sku l fenestra- upper temporal Posterior extended nares, moving to top of head Fusiform body- tapered on ends, more streamline Viviparity- live birth While many mid-Triassic species were not very large – about 2 m in the case of Mixosaurus, some were quite large, such as the 10 m long Cymbospondylus. While most Triassic ichthyosaurs focused on a diet of fish and cephalopods as exemplified by their conical dentition, some appear to have chosen larger prey. Note the elongate body and relatively low-aspect ratio tail typical of the more primitive body of Triassic ichthyosaurs. Small dorsal fin, enlarged front flippers

Answer 320

The clade from which all modern lizards and snakes can trace their ancestry, was well established by the Triassic, with most having likely evolved during the Late Permian or around the Permo- Triassic boundary. One primitive member of the clade still lives today, the tuatara (Sphenodon punctatum) from New Zealand.

Answer 321

Squamata- lead into snakes aqnd lizards Sister-taxon to the Rhynchocephalia (Sphenodon punctatum). A l extant lizards are members of the Squamata and most have developed a rather flexible sku l. Noteworthy is the mobility of the quadrate, which is associated with the loss of the lower-temporal bar that once contributed to the ventral margin of the lateral temporal fenestra. There are 5 main points of flexibility in a typical squamate skull: kinetics of head, boundaries of movement 1- Streptostyly, the ability of the quadrate to rotate about its dorsal articulation with the squamosal/supratemporal;opening jaw 2- Mesokinesis, the ability of the anterior portion of the sku l to rotate about the frontal/parietal suture; 3- Metakinesis, the ability of the parietal to slide fore and aft across the supraoccipital elements at the back of the skull; 4- Hypokinesis, the ability of the anterior part of the palate to rotate about a transverse suture in the palatine/ectopterygoid/pterygoid region; and 5- Amphikinesis, representing simultaneous mesokinesis and metakinesis as influenced by mobility of the quadrate (i.e. streptostyly).

Answer 322

Appear by the Middle Triassic Procumbent dentition Enlarged heavily ossified limb girdles.

Answer 323

Placodontoidea & Cyamodontoidea Placodontoids (seen here) can be distinguished from cyamodontoids by retaining a generally elongate body more typical of other reptiles. They also lack the heavy dermal scutes present in the cyamodontoids. Most basal member of clase May be semi aquaric Plate like teeth Break down shells Placodus As in most placodonts the teeth were designed for crushing – Durophagous- distinctive feature (mollusk eating) Note the elongate body and heavy gastralia below the ribs and covering the belly. Why would these heavy bones be necessary in an animal that fed on the bottom of shallow lagoons? Scoop shaped incisors Have dense heavy bones-weighs animal down, on ocean floor

Answer 324

Thought to be ancestor of turtle but is not Baby like filament teeth- harvesting algae and filtyer feeding- herbivore Note the very broad, turtle-like body. Dentition was quite different from that found in Placodus (previous slide). What was its dentition like? Abundant in the sha low waters of the mid-Triassic of Europe and southern China. Reconstruction of the skull of the placodont Henodus, showing baleen-like filamentous structures along the margins of the upper and lower jaws. Henodus is one of only two known marine reptiles from the entire Mesozoic that appear to have been herbivorous, the other being the pachypleurosaurian sauropterygian Atopodentatus.

Answer 325

Stiffen torso- allows them to move straight in water, just propulsion pushing through water

Answer 326

Unlike placodonts, pachypleurosaurs were primarily adapted to capture fish that occupied coastal shallows. The sku l and jaws are slender and elongate, in contrast to the robust and transversely expanded sku ls of many placodonts. Very different eating habits- more after fish have well ossified limbs and long tail Propuslion- lateral movement A fossil of gravid (pregnant) specimen of Keichousaurus hui was co lected in China and published in 2004. What does vivparity in pachypleurosaurs suggest for sauropterygians? Cheng et al., (2004), Nature 432, pages383–386. Know by fossil evidence and weak connection between pelvis and sacral region- widespread in this grouo- wider birth canal

Answer 327

Generally 1 to 4 metres in length. Elongate bodies with short limbs. Large upper temporal fenestra Primarily fish eating, long-bodied sauropterygians not unlike pachypleurosaurs, but larger and with more fully developed paddles. Teeth at front of snout were procumbent and needle-like – suitable for capturing fish

Answer 328

Note the “hammer-head” form of the snout. What alternative reconstruction once led to this taxon being referred to as “Zipper- head”? A filter-feeding sauropterygian?

Answer 329

The earliest plesiosaurs! Partially reconstructed fossil skeleton of Pistosaurus hadgorni on display at the Senckenberg Research Institute and Natural History Museum Frankfurt. Note the long neck, a feature also seen in many of the later plesiosaurs. Although the paddles are only partly preserved, they can be seen to be broader and much less wing-like than in the Jurassic plesiosaurs.

Answer 330

Although heretical in its argument there are many supporters of a sauropsid link to turtles. Rieppel & deBraga (Nature, 1996) identified a suite of plausible synapomorphies that linked turtles to Diapsids. More recently Sues et al. (Nature, 2015 and cladogram on right) have gone even further (recall our discussion on Eunotosaurus when when we examined the Permian). Turtles are diaspids

Answer 331

Jugal is semi-lunate in early development. urtle orphies Some notable Diapsid/Turtle synapomorphies Absence of a true radiale. Topologicaly it is replaced by a centrale. Ossification pattern of hooked fifth metatarsal differs from mammalian & archosaur pattern. Presence of a single proximale tarsal cartilage during ontogenetic development. Odontochelys (oldest Known turtle - China - 220my) Possible aquatic origins for turtles. Note expanded ribs but no true carapace. Turtle debate- have no temporal fenestra Started to make shell

Answer 332

Proganochelys quenstedi Late Triassic of Germany, Morocco, Greenland, Thailand. Turtle Synapomorphies: carapace & plastron dermal + endochondral bone expansion of ear chamber enclosure of stapes by quadrate.

Answer 333

Triassic Sauropterygia diversified into a number of clades including the durophagous placodonts, whose anatomy was very turtle-like, and a grouping composed of the fish-eating pachypleurosaurs and their close relatives. Herbivory appeared for the first time in marine vertebrates, arising in one placodont genus and in the putative stem-sauropterygian Atopodentatus. The turtles made their appearance in the form of Odontochelys and may have been closely related to Sauropterygia.

Answer 334

What does this cladogram show? Which of the three synapsid clades radiates throughout the Triassic? Which group appears to suffer the most in the transition from the Permian to the Triassic? Why might this be?

Answer 335

Anomodontia: The dicynodonts arose from basal anomodonts sometime in the Middle Permian. Key Traits: Shortening of the preorbital portion of the skull, a condition already incipient in basal anomodonts. Reduction in the size of the dorsal spur of the premaxillae situated between the nasals. Expansion of the lateral plate of the squamosal and the external surface of the zygomatic arch, to increase the surface area available for the attachment of m. adductor externus lateralis. Development of long, convex joint surfaces on the quadrate and articular, permitting fore and aft displacement of the lower jaw during the feeding cycle. Reduction in dorsal premaxilla- middle of nose Extension of pallete Squamosal extension to form zygomatic arch- inc surface area for muscles that attach to jaw- for eating Leaf like teeth- chew plants, common in herbivore Fore and aft- bavk and forth

Answer 336

The dicynodonts arose from basal anomodonts sometime in the Middle Permian. Key Traits: Shortening of the preorbital portion of the skull, a condition already incipient in basal anomodonts. Reduction in the size of the dorsal spur of the premaxillae situated between the nasals. Expansion of the lateral plate of the squamosal and the external surface of the zygomatic arch, to increase the surface area available for the attachment of m. adductor externus lateralis. Loss of teeth on the anterior portion of the occlusal margin of the maxilla, which was covered by a horny beak in life. Expansion of the vomers, which form the anterior margins of the interpterygoid vacuities- space in top of mouth. Great elongation of the temporal fenestrae, which extend posteriorly beyond the level of the foramen magnum and have distinct, dorsoventrally wide medial rims, increasing the vertical surface area available to accommodate enlarged temporal musculature. Deepening of the trough on the lateral surface of the dentary for insertion of the adductor musculature. Development of long, convex joint surfaces on the quadrate and articular, permitting fore and aft displacement of the lower jaw during the feeding cycle. Dorsal displacement of the zygomatic arches, increasing the mechanical advantage of the jaw musculature. Have tusks- 2 Arose from anobanat(previous slide) Changes in skull, most likely changes associated w eating

Answer 337

The dicynodonts arose from basal anomodonts sometime in the Middle Permian. Key Traits: Shortening of the preorbital portion of the skull, a condition already incipient in basal anomodonts. Reduction in the size of the dorsal spur of the premaxillae situated between the nasals. Expansion of the lateral plate of the squamosal and the external surface of the zygomatic arch, to increase the surface area available for the attachment of m. adductor externus lateralis. Loss of teeth on the anterior portion of the occlusal margin of the maxilla, which was covered by a horny beak in life. Expansion of the vomers, which form the anterior margins of the interpterygoid vacuities- space in top of mouth. Great elongation of the temporal fenestrae, which extend posteriorly beyond the level of the foramen magnum and have distinct, dorsoventrally wide medial rims, increasing the vertical surface area available to accommodate enlarged temporal musculature. Deepening of the trough on the lateral surface of the dentary for insertion of the adductor musculature. Development of long, convex joint surfaces on the quadrate and articular, permitting fore and aft displacement of the lower jaw during the feeding cycle. Dorsal displacement of the zygomatic arches, increasing the mechanical advantage of the jaw musculature. Have tusks- 2 Arose from anobanat(previous slide) Changes in skull, most likely changes associated w eating

Answer 338

The diet of Eodicynodon and Emydops, as well as other dicynodonts, required the jaws to have some ability to break down the outer covering of tough plant food. Later synapsids would eventually evolve a sophisticated masticatory apparatus involving complex side-to-side chewing, as seen in modern mammals, Permo-Triassic taxa did not possess this capability. Dicynodonts and some of their contemporaries acquired an excellent functional alternative in that they evolved the ability to slide their mandibles forward and backward, so that food could be sliced apart. Vegetation is tough and nutrient poor need appropriate musculature to chew on plants all day Blue quadrate- linked to atrivulature and moves jaw to allow for movement

Answer 339

Skull gradually shortened anterior to the orbit, and much deeper at the back.- accomadate for muscles Coronoid process of the dentary was reduced dramatically. The coronoid processs is reduced even in Eodicynodon (A & B) and is completely absent in Dicynodon (C & D) and Lystrosaurus (E & F). reorientTION and inc in length- lystrosauras had different eating patterns- more efficient The derived jaw anatomy of Lystrosaurus results in an in-lever (i.e., effort arm of the lever on the power side of the fulcrum or where the musculature applies its force) being shorter relative to the out-lever (i.e., the resistance or load arm of the lever, which corresponds to the side of the lever doing the action) than in basal dicynodonts. What purpose would this lever design support?their feeding mechansims made them dominate this time The lever- weak bite and jaw can open wider Finite element analysis- stimulate bite force of the jaw or force of other muscles Stronger bite force than organisms previously Lystrostarus- had strong bite force but oudenodon has stronger force Earlier ones didn’t rely on force to eat, beaks would of sliced the plants, compensating for weak bite force

Answer 340

Increasing size in dicynodonts Lystrosaurus, which survived across the Permo-Triassic boundary was relatively small, less than a 1 metre long. By the middle Triassic, dicynodonts were growing larger. Kannemeyeria reached lengths of 3 metres, and the Late Triassic Placerias grew larger than 3.5 m and appears to have lived in herds. Start of small living in burrows- avoided harsh daytime

Answer 341

Appeared in the Permian and went extinct by the middle Triassic. They are notable for having survived the end-Permian mass extinction. Predatory, but all Triassic forms were noticeably smaller than their Permian relatives. Why was reduced size an attribute of these Triassic taxa?- easier to maintain metaboliccly Could this have been a result of increasing competition from crurotarsans and avemetatarsalians? Sosyer to cynodoptia

Answer 342

Can you explain the basis for this theory? Does the evidence support alternative hypotheses?- measurable skull distance, bone histology reveals size difference represntitive of minature adults, doesn’t explain why it occurred evoloutionarily Supported by fossil record Side reduction tendency is this effect- tend to survive mass extinctions Red-Permian Purple-Triassic Alternatuve theory- may mature early

Answer 343

Most were small, rarely exceeding 60 cm. There is evidence that they lived in burrows and may have been covered in fur. There is also indirect evidence that they were warm-blooded.- need to have high metabolism, endothermy- can function at optimal rate, don’t need to rely on heat sources One aspect of cynodont anatomy where there is ample evidence is the presence of sophisticated hearing and an ever-increasing brain size. Procynosuchus and the lineage leading to mammals appears to have a tendency to smaller body size. What does small body size suggest for cynodonts? Endotherms- maintain breathing while feeding- forms secondary pallete Loss of ribs in dorsal vertebra From lumbar vertebrae

Answer 344

Note the relatively small bones (coloured) at the back of the lower jaw. • Jaws on the left are in medial aspect and those on the right in lateral aspect. • A- Probainognathus • B- Thrinaxodon Notes Minaturiation and evalaution of mammals- shrink bones in back of jaw Acute hearing is essential for taxa specialized to hear high frequency sounds. Being small, cynodonts probably fed more on arthropod prey, which are likely to produce higher frequency sounds. Evolution of the hearing ossicles The position of the primitive post-dentary jaw bones were perfectly placed to detect sound. Initially, low frequency vibration was likely picked up by the bones at the back of the jaw. As selective forces continued to favour sound detection and as synapsids became smaller as they evolved from the Permian carnivores such as Dimetrodon to the small insectivores of the Triassic, prey choices also became smaller and the sound they produced became increasingly higher frequency. Emergence of cmj- permitted miniaturization of dentry elements inc hearing functiokn Muscles for jaw articulation being co-opped for middle ear

Answer 345

Post dentry bones feee to vibrate and had stabilization of jaw Limited vibrating of ossicles- cant hear high frequency Jaw bones become middle ear bones Quadrate and articular vibrate freely Larger area of tympanic membrane Only birds share with mammals the capacity for rapid juvenile growth, and it is not coincidental that birds also resemble mammals in exhibiting a high metabolic endothermic physiology. What do these graphs show? Morganucodon, a shrew sized insectivore that represents the real mammaliaforms.- halted growinh in juvenile Was small size necessary for mammal anatomy to evolve?- allowed to evolve true tympanid ear

Answer 346

Early Triassic terrestrial habitats were dominated by synapsids, with dicynodonts accounting for the vast majority of herbivores. Carnivorous therocephalians were also common, but did not survive beyond the Middle Triassic. Cynodonts diversified in the Middle Triassic and gave rise to proto-mammals (e.g. Morganucodon) by the Late Triassic. The synapsids that survived into the Late Triassic were miniaturized, burrow-dwelling, and almost exclusively nocturnal or crepuscular. Advances in the synapsid hearing system culminated in the first appearance of a true impedance-matching ear in the group. Become endothermic to inc metabolic activity, can be more active, can function more efficently

Answer 347

The appearance of the ”Ruling Reptiles” Affinities to younginiforms are debated Archosaurus rossicus Latest Permian Best-known Permian archosauromorph Enlarged premaxilla for dramatic overbite Preorbital fenestra shallow ventral ridge •Elongate narrow centrum •Zygodiapophyseal laminae •Elongate parallelogram shaped centrum

Answer 348

Tending to develop a parasagittal gait. Development of fully ossified braincase (possibly associated with feeding adaptations). Initially exclusively terrestrial (later forms secondarily aquatic).

Answer 349

An agile active predator. • What does this reconstruction suggest about the ecological role filled by this taxon? • Notice the antorbital and mandibular fenestrae - a trait that distinguishes archosaurs from other reptiles. One Triassic form with an unusual anatomy! Take a look at the long neck and more specifically the very long cervical centra.

Answer 350

Drepanosauromorpha is sister-group to Trilophosauridae among archosauromorphs, thus implying the paraphyly of ‘Avicephala’. Distinctive, triangular skulls, resembling bird skulls. Avicranium, had pointed, toothless, bird-like beak A suite of bizarre, almost chameleon-like skeletal features e.g. two fingered hands, shoulder hump Prehensile tail with claw at the end – arboreal lifestyle?

Answer 351

s Trilophosaurus a Tree Climber? What is the source of the evidence? Can the dentition help us make sense of the claws? Conifers were common in the Triassic? What might this suggest?

Answer 352

The Rhynchosauria are archosauromorphs slightly more derived than Tanystropheus and Trilophosaurus. The earliest members of the clade, such as Howesia and Mesosuchus, measured less than 1 metre in length, but later forms such as the Late Triassic Hyperodapedon "Scaphonyx" would exceed 2 metres

Answer 353

Late Triassic, Kyrgystan Elongate head, very long legs, and a membranous structure – for what purpose? The first delta-winger glider

Answer 354

ssic, Kyrgystan A stem saurian or archosauromorph? Mysterious skin appendages feathers? scales? Or neither?

Answer 355

Early Triassic, South Africa Poorly preserved but demonstrates several lepidosauromorph characters, including… Subpleurodont dentition Quadrate conch Reduced lacrimal Absence of the lower temporal bar A bowed posterior surface of the quadrate

Answer 356

Lizard-like, highly specialized lepidosauromorphs Gliders and parachutists Modifications of the quadrate and no lower temporal bar

Answer 357

Retains a lacrimal in the skull that is considerably reduced, more advanced members lose it completely Pleurodont dentition, teeth attached to a shelf on the inner side of the jaw Typical lepidosauromorph characters e.g. quadrate conch Gephyrosaurus is the most primitive member of Rhychocephalia, the group represented today only by Tuatara Clevosaurus sp Late Triassic Similar morphologies of the skull to Sphenodontian reptiles i.e. Tuatara Insectivorous

Answer 358

Saurian reptiles have a modest beginning but would experience one of the largest radiations in the history of terrestrial vertebrates as they move into many of the major niches in the Mesozoic There is a dramatic degree of experimentation along the saurians stem and in the earliest stages of saurian evolution Lepidosauromorpha and Archosauromorpha had diverged from one another by the Early Triassic, and the two clades went on to undergo extensive adaptive radiations by the Middle Triassic. • Saurian reptiles likely originate in the early-middle Permian • The fossil record for the earliest stages in lepidosauromorph evolution is extremely poor • Several stem saurians/neodiapsids have some lepidosauromorph affinities e.g. lizard-like body plan, morphologies of the foot, lack of a lower temporal bar

Answer 359

Continuing from the end-Permian mass extinction, The Triassic was a difficult place for vertebrate life, both on land and in the sea. The Sauropterygia, which would go on to dominate the Jurassic seas, appeared and began to diversify. • The Ichthyopterygia. or fish lizards, evolved. Upper Norian •Dinosaurs originated, and representatives of all the major clades appeared during the Late Triassic. • Advanced synapsids appeared, in the form of stem-mammals such as Morganucodon. 227 237 Carnian • Lepidosauromorpha and Archosauromorpha diversified. • Pterosaurs appearec • Turtles (Pappochelys and Odontochelys) made their appearance Ladinian some time in the Middle Triassic. • Dicynodonts were the most successful herbivorous clade 242 Middle Lower Anisian throughout the Middle Triassic. • Stereospondyls became dominant freshwater predators. 247 Olenekian Induan • Oxygen levels dropped to 12%, temporarily confining terrestrial life to low-altitude regions. Evidence from oceanic cores • Cores dating to the period point to a very harsh oceanic environment that was not suitable for aerobic life. • Note the very narrow band suitable for aerobic life in the Triassic oceans.

Answer 360

There is strong evidence for athermal maximum event about 1.5 million years after the beginning of the Triassic, at the very beginning of the Olenekian. • Temperature proxies for this period, in the form of δ18O apatite and δ13Ccarb isotopic ratios, indicate that surface water temperatures at equatorial latitudes can be conservatively estimated to have approached 38˚C and may have exceeded 40˚C. • Onland, temperatures would likely have been even higher, possibly exceeding 45˚Con average. • At temperatures above 35˚C, photorespiration dominates over photosynthesis in C3plants (a process by which plants take in oxygen and give off [respire] CO2),and very few plants survive temperatures of sustained global temperatures over 40˚C.

Answer 361

The role of CO2in the Early Triassic • Strong evidence exists for ever-increasing levels of atmospheric CO2 during the EarlyTriassic, which through afeedback system resulted in both extreme heat and severe depletion of atmospheric oxygen, the underlying cause of the increasing CO2 levels has remained difficult to pin down

Answer 362

CAMP(Central Atlantic Magmatic Province) • The rift that led to the eventual formation of the Atlantic ocean was on land during the Triassic (see previous slide) and as such the CO2 emissions would have had a much more pronounced impact on the atmosphere than the rift, which is a few thousand metres below the surface, at the bottom of the Atlantic ocean, has today. Iceland is the only surface reminder of this rift today

Answer 363

Lower Triassic Jawed Fish • The sharks and specifally the neoselachians, the group from which all modern sharks evolved are well established, but all fossils appear to be restricted to what is present-day Europe. • The oceanic anoxia of the Lower Triassic may have reduced shark diversity

Answer 364

BonyFish (Neopterygia) • Three new neopterygian clades appear during the Triassic, and are an example of life taking advantage of an opportunity. • It is important to keep in mind that while the Triassic was certainly a harsh period in earth’s history, it does not mean that all vertebrate life was significantly handicapped. • The Halecomorphi (bowfins) appear to have benefited from the opportunity.

Answer 365

Ginglymodi who have modern relatives known as gars, appearto have taken advantage of the Triassic upheaval and make their appearance in the middle Triassic. • One such taxon is Kyphosichthys grandei from the Middle Triassic of China

Answer 366

The Most successful Triassic Fish (Teleostei) • While not as abundant in the Triassicas the halecomorphs or ginglymodians, they contain a number of species that were the ancestors of the vast majority of modern bony fish alive today. • Sometime in the Middle Triassica taxon that probably closely resembledPholidophorus, a small 40-cm-long herring-like neopterygian that occupied the ever-growing Tethys during the Late Triassic, gaverise to the rest of the Teleostei.

Answer 367

Distinct supramaxillae. • 2- An extension of the myodome (i.e. buccal muscle chamber) into the basioccipital (i.e. basal element of the braincase). • 3- Ural neural arches that are specialized and reduced in number (termed uroneurals) • 4- Premaxillary complex comprising paired lateral, mobile, tooth-bearing elements and a single midline element (the dermethmoid). • 5- Quadratojugal that is fused to the quadrate. • 6- Vomers (anterior elements in the palate) that are fused into a single bone.

Answer 368

The temonspondyls, which were the most common Permian anamniotes gave rise to the most abundant Triassic clade the stereospondyls.

Answer 369

• Some taxa were large and appearto have served an ecological role similar to that of modern crocodiles, at least during the Lower Triassic. • Life reconstruction of the trematosaur Trematosaurus in its natural habitat, a shallow lagoon or freshwater swamp

Answer 370

Continuing a trend that began in the late Permian, oxygen levels plummeted to as low as 12%, resulting in severe anoxia in the deep oceans and at high altitudes on land. • Temperature skyrocketed, reaching global, annual averages of over 30°C. Entire regions of the planet, including shallow marine environments, became uninhabitable, and terrestrial vertebrate life almost went extinct. • Life recovered in the Middle Triassic, which saw a diversification of marine and terrestrial vertebrate faunas. • By the Late Triassic, extensive volcanism and tectonic activity had resulted in the break-up of Pangaea. One large volcanic region, the Central Atlantic Magmatic Province (CAMP), began to separate Africa and Europe from North America. Outgassing of CO2as a result of CAMP activity appears to have been a major factor in the end-Triassic extinction. • Conodonts were the only jawless fish that left evidence of their presence in the Triassic record, and were extinct by the end of the period. Fossils of hagfish and lampreys are lacking, but this likely reflects preservational bias. • Jawed fish continued to diversify to some degree, and teleosts made their appearance. Sharks were present, but did not yet include pelagic predators. • Among anamniotes, only Stereospondyli survived beyond the end of the Permian, if lissamphibians are considered stereospondyls. These specialized temnospondyls came to dominate Early Triassic freshwater habitats, in which they filled essentially the same niche as modern crocodilians.

Answer 371

Crown Mammalia • What is a crown group? • Why is its definition essential for understanding the evolution of a group in this case Mammalia? • Could the end-Triassic extinction have led to the evolution of crown mammals? • What is the evidence? • How can a case be made in support of crown mammals having evolved as a result of the end-Triassic extinction?

Answer 372

Small – shrew-sized. • The braincase is larger than in cynodonts, and it is likely that enhanced sensory capacity of the middle and inner ear is partly responsible for the enlarged brain as an increase in sensory capacity would have been necessary for the additional input coming from the inner ear. Morganucodon (A Mosaic) • While quite mammal-like, this taxon lacked an auditory bulla, which is a chamber on the ventral, posterior portion of the skull of crown mammals that encloses the middle and inner ear and is formed by the tympanic, which is a derivative of the articular. • The fact that the articular retains its position relative to the lower jaw in these basal mammals such as Morganucodon suggests that a fully functional modern mammalian hearing system was not yet fully developed

Answer 373

Morganucodon jaw remains primitive • Note the retention of the post-dentary bones. • What does the continued existence of the post-dentary bones in the jaw suggest about jaw function? What does it also suggest about hearing in mammaliaforms

Answer 374

Morganucodon dentition • Clearly differentiated into incisors, canines, premolars and molars. • In Morganucodon, as in crown mammals, the molars have additional cutting surfaces along the lingual and labial margins of the teeth, known as cingula (singular: cingulum). • In Morganucodon the molar possesses multiple cusps, but the three primary cusps are essentially in a line – a primitive condition for Mammaliaformes, and an indicator of a relatively unspecialized diet.

Answer 375

Morganucodon Post-cranium • Cervical ribs are not fused to the cervical centra, a primitive condition and unlike all crown mammals. • Trunk (dorsal) vertebrae are separated into thoracic and lumbar series (as in the Triassic cynodont Thrinaxodon). • Lumbar vertebrae lack ribs and their zygopophyses are oriented at an an angle of 45˚ to the horizontal axis. • What might be the function for the angle? • Unlike Thrinaxodon and like crown mammals, the neural spines are short and the orientation of the spines alternates in direction between the thoracic and lumbar series. • What is the orientation and why might this be so?

Answer 376

Morganucodon (Shoulder Anatomy) • Reconstructions in lateral view of the left shoulder girdles of three mammaliaforms: a generalized cynodont such as Thrinaxodon (left); Morganucodon (centre); and an extant monotreme. • Note that the glenoid (shaded) is laterally oriented in the cynodont and Morganucodon, but has a ventrally oriented dorsal portion in the echidna. • What does the different orientation of the glenoid suggest?

Answer 377

in lateral view of the left pelves of the mammaliaform Morganucodon (left) and a modern eutherian tree shrew (right). • Note the “rod-like”, anterodorsally directed iliac blade, a typically mammalian feature associated with reorientation of the pelvic musculature and elaboration of the gluteal muscles into the primary femoral retractors

Answer 378

Based on the two competing phylogenies (see earlier slide), where do monotremes fit? • Poor fossil record has made the conclusive assignment of the Monotremata controversial. • While molecular data support a divergence time between monotremes and therian lineages to have occurred before the split between Metatheria (marsupials) and Eutheria (placentals), the fossil record suggests a very different picture with the oldest monotreme fossils being younger than the oldest therian fossils

Answer 379

Multituberculata • Rodent-like mammals date to the middle Jurassic. • Unique dentition which is characteristic of the clade. • Reconstruction of the left mandible (dentary) of the Jurassic multituberculate Rugosodon eurasiaticus from China. Note the very distinct fourth premolar (highlighted in yellow), showing the pattern of rugose tubercles that is so diagnostic of Multituberculata.

Answer 380

Aside from specialized dentition, Rugosodon also had a very peculiar ankle morphology. • What function might have this ankle morphology have served?

Answer 381

Reconstruction of a euharamiyidan in an arboreal pose, showing the prehensile tail and also the prominent dentition that is reminiscent of the Multituberculata.

Answer 382

Takeaways from Jurassic Part 2 • Evolution of Mammaliaformes, and the current debate regarding the phylogenetic position of Multituberculata • Crown-group Mammalia, and the importance of the enigmatic haramiyids for establishing the composition of the crown-group • Morganucodon, and how developments in the Jurassic contributed to the evolution of mammalian hearing and the later radiation of Mammalia • The role of miniaturization in the evolution of the modern mammal morphotype • Orientation of the limbs in early mammals, and the evolution of homeothermy • What do monotremes reveal about the evolutionary path toward therian mammals? • The unusual dentition of multituberculates, and the significance of this group in early mammalian evolution

Answer 383

• While generally the Jurassic saw the replacement of crurotarsan crocodylomorph terrestrial predators with avemetatarsalians, this was not always the case. • Razanandrongobe sakalavae Middle Jurassicof Madagascar

Answer 384

• While generally the Jurassic saw the replacement of crurotarsan crocodylomorph terrestrial predators with avemetatarsalians, this was not always the case. • Razanandrongobe sakalavae Middle Jurassicof Madagascar

Answer 385

Crocodylomorphs and their modern niche! • While present-day crocodiles inhabit semi- aquatic or fully aquatic niches, their Jurassic counterparts continued to display a primarily terrestrial assemblage with both small, fleet-footed forms (Litargosuchus) and some large predators (see previous slide). • The modern-day niche preference did not become fully established until the Cretaceous and we will revisit them when we explore the Cretaceous.

Answer 386

evolution of membraneous wing -divergent pedal digit -prepubis (supports gut) -enlarged skull -hollow bones What aspect of this anatomy speaks to the primitive nature of these Triassic forms Wing- elongate 4th finger. Evolution of Pteroid supported anterior margin of the wing membrane • Pedal posture has always been an intriguing question that has puzzled palaeontologists for well over a century. • Reconstruction of the left pes of Dimorphodon , showing a digitigrade pedal posture with the metatarsals off the ground. Note the bent fifth digit. Based on this reconstruction, the fifth digit would produce a small, possibly circular impression behind the main footprint. Although ichnofossils of Dimorphodon are unknown, those of contemporaneous pterosaurs such as Campylognathoides suggest a similar foot posture. Dorygnathus sp. in the fully quadrupedal pose that has been postulated for all Jurassicpterosaurs. The “fur - like” covering is based on preserved traces of afine layer of epidermal integumentary material that might have provided insulatio

Answer 387

Theloss of the long tail! An example of one of the earliest pretodactyloid pterosaurs - Kryptodrakon progenitor (approximately 1.5 metre wingspan), from Oxfordian Stage deposits just above the Middle -Upper Jurassicboundary in China.

Answer 388

Triassic pterosaurs were generally small and believed to either be insect hunters of possibly preying on small fish. • At least one Jurassic form appears to be well adapted to filter -feeding – Liaodactylus . • What evidence do we have for this feeding preference? • How confident are palaeontologists in that interpretation? • What alternative feeding strategies might present themselve

Answer 389

Liaodactylus • Examine the skull closely. • Can you see the reason why the filter-feeding hypothesis was put forward? • Would you support that hypothesis

Answer 390

Pterodactylus antiquus • Thefirst pterosaur ever discovered near the end of the 18th century. • What pterodactyloid traits can you detect? • SomePterodactylus specimens that have been collected over the last 200 years even retain impressions of muscle fibre

Answer 391

The most critical and arguably the most significant event in the evolution of Jurassicpterosaurs was the major radiation that occurred during the Tithonian at the very end of the Jurassic. • At this point in pterosaur evolution, the short-tailed pterodactyloids diversify into a myriad of ecological roles and the stage is set for the impressive forms that come to dominate the Cretaceous.

Answer 392

transition from small, cursorial crocodylomorphs to large, aquatic ones • Could some large terrestrial crocodylomorphs have existed in the later part of the Jurassic? If so, why? • Pterosaurs underwent a major radiation during the Jurassic, and two new, important clades appeared • Did pterosaurs walk on all fours, or were they bipedal? Fossil evidence form the Jurassic has shed some light on this question, but what conclusions does this evidence suggest? • Darwinopterus modularis and the transition from long-tailed to short-tailed pterosaurs • How has the study of pterosaurs provided a striking example of of “Modular Evolution”? • Anurognathids and the evolution of the Jurassic pterosaurs • The importance of dentition for inferring pterosaur diets – does heterodonty suggest insectivory? • The Solnhofen limestone, the appearance of the Pterodactyloidea, and the early history of pterosaur studies

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