lec 12 Flashcards
(40 cards)
PACHYCEPHALOSAURIA –
- Late Cretaceous of Asia & North America
- Thickened skull roof
- Short ‘frill’ (squamosal) over occiput (back of skull)
- Osteoderms on squamosal
- Obligate bipeds
- Short arms & hands
- Stenopelix, Early Cret. Germany ~ 2 m total length Originally considered to be a basal pachycephalosaur; now considered to be a basal ceratopsian (sister taxon to Yinlong)
- Dracorex (juvenile) Stygimoloch (subadult) Pachycephalosaursus (adult) – as the animal grows it reabsorbs horns on the skull into the body
Development of the Dome
Growth series of Stegoceras validum in dorsal (top) and lateral (bottom) views
Note transition from a flat-headed to domed frontoparietal morphology that occurred through ontogeny
YINLONG DOWNSI XU – earliest member of Ceratopsia – most basal member
Early Late Jurassic, Shishugou Formation of Xinjiang, China
Forelimb <40% hindlimb
Rostral (1) Skull larger than most ornithischians but < other ceratopsians
Thickened jugal, but no flange – no horn (2)
Elevated post skull but no parietal contribution to frill (3)
PSITTACOSAURIDAE Osborn 1923
123-125 Ma (Barremian-Aptian boundary) – mid Albian (~ 112 Ma)
Skulls short and tall.
Adults bipedal; hatchlings probably quadrupedal
Dentary teeth with bulbous primary ridge
Tails have “quills” – modified scales of some sort
Bonebed accumulations suggest social behaviour
NEOCERATOPSIA
Defined by the presence of a well-developed frill
Basal members biped
Frill Size Increases throughout Ceratopsian Evolution
AQUILOPS = Early Cretaceous, Montana
Oldest North American ceratopsian
Aquilops is a basal neoceratopsian
Shows connection between Asia and North America ~105 million years ago
LEPTOCERATOPSIDAE
Unique horizontal shelf (notch) on teeth
Vertical-notch tooth-wear pattern was produced by both vertical shearing and grinding
More basal neoceratopsians exhibit an oblique wear pattern vs. more derived neoceratopsians with a vertical shear wear pattern
1st non-ceratopsid neoceratopsian to be described
Mid-caudal neural spine height 4x centrum height. (1)
KOREACERATOPS HWASEONGENSIS
First dino to be found in Korea
Outgroup to more derived neoceratopsians.
Very tall neural spines over 5 times higher than the associated.
centra in the distal caudals.
Claws, not hoofs.
Probably functionally bipedal
CORONOSAURIA = Protoceratopsidae + Ceratopsoidea
Enlarged frill, enlarged skull, obligate quadrupedality
Ceratopsians laid soft-shelled eggs and that’s why there are no found ceratopsian eggs
CERATOPSOIDEA = Ceratopsidae + closest sister taxa (e.g., Zuniceratops)
Large body size (.5 to 2 tons)
Postorbital brow horns are a synapomorphy
Might have burrowed
Double rooted teeth
ZUNICERATOPS CHRISTOPHERI – New Mexico
Postorbital horncore mediolaterally compressed
No nasal horn.
Two replacement tooth rows with single-rooted teeth
CENTROSAURINAE
Relatively short, deep snout
Pair of long horns (P3) at back corners of the frill
Short, rectangular squamosals
CHASMOSAURINAE
Longer, shallower snouts
Elongate rostral bones
Long squamosals
CERATOPSIAN SOCIAL BEHAVIOUR
Ceratopsid bonebeds are common in the Campanian of W NA, esp. for centrosaurines: Coronosaurus, Centrosaurus, & Pachyrhinosaurus
Carcasses are disarticulated
>100000 elements preserved from 100s or 1000s of centrosaurs
All size classes preserved
EVOLUTIONARY PATTERNS IN MARGINOCEPHALIA
- FEEDING
Pachycephalosaurs have relatively unspecialized snouts and teeth, and so were probably nipping browsers
Basal ceratopsians increased their jaw power and evolved the cropping rostral bone (+ predentary = ‘beak’)
The frill of basal ceratopsians greatly increased their jaw muscle power
Shearing dental batteries in Ceratopsidae gave them one of the most powerful bites to evolve among amniotes
EVOLUTIONARY PATTERNS IN MARGINOCEPHALIA
-LOCOMOTION
Pachycephalosaurs, basal ceratopsians, and basal neoceratopsians were bipedal
Increased skull size forced advanced neoceratopsians onto all fours, such that Coronosaurs were obligate quadrupeds
EVOLUTIONARY PATTERNS IN MARGINOCEPHALIA
-SIZE TRENDS
Most pachycephalosaurs, basal ceratopsians, and basal neoceratopsians were small (all in the 1-3 m range, smaller than humans)
Increased size in pachycephalosaurs (e.g., Pachycephalosaursus) only occurs at the very end of the Late Cretaceous.
For most of its history, Ceratopsia consisted of only small dinosaurs.
Advanced neoceratopsians show a size increase earlier than pachycephalosaurs, culminating in the major size increases at the base of Ceratopsoidea
PATTERNS IN MARGINOCEPHALIA
-SOCIAL BEHAVIOUR
Both pachycephalosaurs and ceratopsians seem to have used their heads for within-species interactions.
Ornamentation (marginal osteoderms, domes, frills, horns, etc.) and possible combat features (thickened skulls, horns) are present in both clades, and some of these only appear at fully adult sizes.
Evidence for gregarious behaviour is present throughout Ceratopsia (e.g., Psittacosauridae, Leptoceratopsidae, Protoceratopsidae, Ceratopsidae)
CERATOPSIAN PALEOBIOGEOGRAPHY
- Ceratopsia originated in Asia (Late Jurassic)
- Initial radiation of neoceratopsians in Asia (Early Cretaceous).
- Dispersal of basal neoceratopsians into Europe before Bering Land Bridge (late Early Cret.). – entry of Leptoceratopsid ancestor into NA via Europe.
- Radiation of basal neoceratopsian in NA via land bridge ~Turonian.
- Origin of ancestral ceratopsid equivocal (Turanoceratops in Asia, Zuniceratops in NA in Turonian).
- Radiation of ceratopsids in NA; possible Late Cret. return of Leptoceratopsids to Asia (Udanoceratops); possible return of ceratopsids to Asia.
LEC 13 - ORNITHOPODA
ORNITHOPODA = Parasaurolophus and all taxa closer to it than to Triceratops
Ornithopoda (“bird feet”)
Basal ornithopods have 4 toes supporting weight; Styracosterna have 3 functional toes
Evolved in the Early Jurassic, survived until the end of the Cretaceous.
Consist of basal ‘hypsilophodont-grade’ taxa (e.g., Thescelosauridae), and large clade of iguanodontians, including hadrosaurs
Primitively ornithopods were small, agile bipeds. Iguanodontians were generally much larger, and quadrupedal.
Hypsilophodon from the Early Cretaceous of England is an archetypical ‘basal’ ornithopod
Most complex jaw vertebrate
‘Basal Ornithopoda’, often referred to as ‘hypsilophodonts’, are ornithopods less derived than Styracosterna
Most are Early to Late Cret., so not basal temporally, but phylogenetically
All are bipedal, but most not well-adapted to fast running
Lack defensive mechanisms
Feathers: Kulindadromeus zabaikalicus (2014)
Middle to Late Jurassic (175 Ma), Siberia
Oldest ornithischian with feathers.
Combination of modified scales and feathers on body.
Multiple specimens from bonebeds = sociality?
Orodrominae
Early to Late Cret. NA & Asia
Oryctodromeus = 1st dino to show burrowing and denning behaviour
Adult & 2 juveniles found in ~2x1 m den
Bipedal with forelimb adapted for digging
Hypsilophodontidae
Early Cretaceous, Isle of Wight
1st discovered 1849; named 1869
~2m long; ~ 20 kg; agile runner;
Pointed snout with sharp beak for snipping plants
Thescelosauridae
Early to Late Cret. of North and South America, & Asia
Cone-like teeth in premax; leaf-shaped teeth in dentary and maxilla
Long snout, larger body size than more basal ornithopods.
Most 2-4 m, but some up to 6 m
5 fingers, 4 toes
Watch Michael Hudgins talk for more details on basal ornithopods and Thescelosauridae
