Origin of mammals Flashcards
(56 cards)
1
Q
Earliest known synapsid
A
Archaeothyris, 310 mya
2
Q
“pelycosaur” timings
A
upper carboniferous to middle permian
3
Q
“therapsid” timings
A
mid Permian to end Permian
plus a few groups persisting
4
Q
“cynodont” timings
A
upper Permian to upper triassic
5
Q
First mammaliaform date
A
200 Ma
6
Q
Cenozoic
A
Carboniferous-Permian-Triassic-Jurassic-cretaceous
7
Q
Eothyris
A
2 enlarged canines
Temporal fenestra
but broad skull and supratemporal bone (basal)
8
Q
caseids
A
eg. Cotylorhynchus
highly adapted for herbivory; blunt leaf life teeth,, large temporal fenestra for strong jaw closure, large belly, short skull, up to 3m long
9
Q
Eupelycosauria
A
Clade- includes some pelycosaurs, therapsids etc
eg. Ophiacodon
long jaw w short pointed teeth for piscivory
10
Q
Sphenacodontids
A
Advanced carnivorous pelycosaurs
eg. Dimetrodon
large sharp canines, simple jaws and otherwise undifferentiated teeth, powerful jaw
short sprawling limbs
11
Q
Edaphosurids
A
eg. Edaphosaurus herbivorous dentition large temporal fenestra tooth plates short wide jaw
12
Q
Pelycosaur palaeoecology
A
around 50% of terrestrial populations were carnivores, therefore appears they remained close to water, and relied on its productivity in order to support higher trophic levels
however, hard to get accurate information from this distribution due to taphonomic biases, if living near water is it more likely that carnivores will be preserved?
13
Q
Biarmosuchia
A
most basal therapsid group
moderately sized carnivores
eg. Biarmosuchus, Russia
or Hipposaurus, South Africa
14
Q
Pelycosaur and therapsid similarities
A
enlarged canine, reflected lamina of the angular, strongly built back of skull
15
Q
therapsid characters
A
more heterodont, shorter jaws, bigger temporal fenestra, choanal trough in palate, limbs not sprawling and ribcage off the ground, reduced tail size, more gracile shoulder girdle
16
Q
therapsid bone histology
A
higher rates of growth seen in fibro-lamella of bones
17
Q
therapsid palaeogeography
A
could live at higher latitudes and tolerate seasonality
by middle Permian could reach higher latitudes through passage of ‘summer wet’
no competition in new areas so radiation of new ecotypes
proportionately fewer carnivores (3%) so fully terrestrial
18
Q
4 different therapsid groups (distinguished by jaw structure and function)
A
Dinocephalia
Gorgonopsia
Anomodontia
Therocephalia and Cynodontia
19
Q
Titanophoneus
A
Primitive dinocephalian
heavily built skull and body
carnivorous
developed canines millions of years before the gorgonopsids
20
Q
Anteosaurus
A
Dinocephalian
Carnivorous; large canines, interlocking teeth, large skull
21
Q
Moschops
A
herbivorous dinocephalian
big chest, ripping teeth, heavily built, 2-3m long
22
Q
Otsheria
A
Anomodont/ dicynodont small and basal short skull large temporal fenestra teeth not differentiated Permian of Russia
23
Q
Dicynodon
A
Anomodont/ dicynodont
large temporal fenestra
short jaws
lost all teeth- just has horny tooth plates/ beak like (not preserved but can tell from skull)
24
Q
Lycaenops
A
Gorgonopsid late Permian top carnivores huge teeth- canines for killing, incisors for tearing (first known sabre teeth), can't chew big bodies gracile limbed
25
Regisaurus
```
Therocephalian
carnivores
large canines
large temporal fenestra
reduced tail
mammal-like ribcage
survived end Permian mass extinction
```
26
Procynosuchus
```
Cynodont
upper Permian
small carnivore
secondary palate
multicusped postcanines and differentiated dentition
dentary bigger than post dentary
large, elongated temporal fenestra
skull has sagittal crest (present as a result of temporal muscle development) and zygomatic arch
```
27
The Great End Permian Mass Extinction
200mya
largest ever- over 90% of plant and animal life lost, including 95% dicynodonts, all gorgonopsids
due to volcanic eruptions in Siberia 250mya, releasing CO2 and warming atmosphere, and SO2 and making acid rain
Can see volcanic evidence in Siberian traps
28
Faunal changes across Permian-Triassic boundary
phase 1- lowering of water table, fewer ground plants, lose small carnivores and herbivores over 21,000 years
phase 2- increased seasonality, more hot and arid, lose larger plants. Loss of riverine vegetation means bare, fast-flowing rivers. Lose large herbivores and carnivores over 33,000 years (main extinction)
phase 3- onset of permanent arid conditions, very inhospitable, life lost over 8,000 years
29
End Permian mass extinction survivors
Lystrosaurus
dicynodont with teeth, most widespread herbivorous genus on Earth, every continent except Antarctica
survived because lived in burrows and ate plant tubers that grew underground
Kannemeyeria
dicynodont
Regisaurus
therocephalian, small bodied
Cynodonts such as Thinaxodon
burrower
had more progressive physiological regulation of temperature and osmotic pressure, may have helped survival
Can also see cynodont survival due to faster growth, earlier reproduction, shorter lifespan, smaller size in bone annual growth patterns
30
Thrinaxodon
Cynodont
teeth have extra cusps
secondary palate - increases rate of breathing, aids complex mastication because separates air from food
large dentary
pelvic girdle point forwards
reduced tail as limb moving muscles on pelvis
thorax raised off ground because of new gait, increases lung capacity
ribcage in just thoracic region indicates diaphragm attachment
survived Permian mass extinction
31
Cynognathus
```
Eucynodont
middle Triassic
big canines- carnivorous
sectorial hind teeth
tiny reflected lamina of angular and hinge bones
```
32
Massetognathus
Diademondontid (Eucynodont)
| Knees turned in to body, short thin tail, broad, basined teeth w cutting rims for grinding plants
33
Tritylodontids
eg Kayentatherium
Rodent-like teeth, multi rooted, w rows of crescentic cusps for grinding up food
No longer has bone between eye socket and temporal fenestra (post orbital bar)
34
Tritheledontids
eg. Pachygenelus
no postorbital bar
large dentary contacts squamosal
35
Morganucodon
early mammaliaform
upper Triassic
brain 4x larger than early stem mammals and enclosed w bony side wall
multicusped, mulirooted molars that work with triangular movement
only a few plesiomorphs: unfused atlas, cervical ribs, no supraspinatus fossa on scapula
36
Pelycosaur jaw closing musculature
temporal fenestra allowed musculature to be put onto lever arms for greater jaw closing force
adductor mandibularis
origin around edges and across temporal fenestra, and insertion onto upper edge and the connective tissue of coronoid eminence
37
therapsid jaw closing musculature
larger temporal fenestra
pterygoideus muscles pulls jaws forwards
capiti mandibularis pulls jaws back
balance of two forces makes jaw more powerful
pterygoideus orgin in palate, goes backwards and attaches to inner jaw surface (reflected laminar of angular= lever arm)
38
early cynodont jaw closing musculature
capiti mandibularis muscle divided into two, temporalis (inner) and masseter (outer), attach at back of temporal fenestra.
Temporalis pulls jaw inwards and upwards,
masseter pulls jaw outwards and upwards, forces from each balance
Combination of power and accuracy
39
advanced cynodont jaw closing musculature
eg. Chiniquodon
masseter muscle as big as temporalis, slits into deep masseter and superficial masseter
latero-medial balance of forces
deep angular region in lower jaw allows masseter lever arm
muscles rearranged to maximise force at teeth rather than at hinge
40
corresponding jaw and ear bones
```
incus = quadrate
malleus = articular
stapes = stapes
ectotympanic = angular
```
41
Theories for jaw bones to ear ossicles
1. already had stapes, and other bones later joined in
| 2. jaw bones at back of skull were already aiding hearing (correct)
42
Increasing pressure of sound in impedence matching by
1. area effect- make tympanic membrane larger than fenestra ovalis
2. lever arm effect - ear ossicles form lever system, where lever to fenestra ovalis smaller than lever to tympanic membrane (lever = 1.5 x longer)
increases pressure by 30 x
43
Aliin's theory
1978
| Cynodonts could impedence match because sound could be picked up by bones at back of jaw
44
General mammal features
atlas and axis modified for extensive head mobility (dorso-ventral, rotation around long axis)
flexible cervical vertebrae
2 regions of dorsal vertebrae (with and without ribs)differentiated thorax and lumbar vertebrae
highly mobile shoulder girdle
hip muscles attached to femur head, decreases moment of inertia
parasagittal stance
tuber calcis on ankle
45
Reptile vs mammal locomotion mechanics
speed and metabolic cost the same
but maximum sustainable aerobic speed higher in mammals (endurance)
reptile max sustainable speed about 10x lower
due to muscle physiology and oxygen provision
46
Basal tetrapod locomtion
Lateral flexion of axial skeleton
Limb protraction-retraction
Long axis rotation of femur/humerus
Limb extension to push forwards
47
Muscles at pelvis (pelycosaur)
ilio femoralis - lift limb off ground
pubo-ischio-femoralis internus- pulls leg forwards
pubo-ischio-femoralis externus - puts limb on ground and contracts to hold body weight
caudi femoralis - pull femur back (biggest muscle in body- in tail)
48
Mammal muscle positions at pelvis
ilio femoralis extends forwards, up illium and attches to greater trochanter at back of femur head, forms gluteal muscle, pulls leg back
pubo ischio femoralis internus shifts up and forwards and attaches to trochanter minor. Forms psoas and acus muscles, pulls legs forwards
tail reduced and caudi femoralis reduced and lost as retractor
49
Dual- gait hypothesis
Therocephalian therapsid
femur fits into acetabulum parasagittally and in a sprawling stance
muscles would also work for both forms
extra joint between astragalus and calcaneum, potentially allows both flexion and rotation of ankle to allow both stances, as in a crocodile
(but it is a different joint/walk)
50
Forelimb changes pelycosaur --> therapsid
shoulder girdle more mobile, increases stride length
(~50% stride of forelimb due to movement of scapula on ribcage)
forelimb shorter than hindlimb, scapula increases stride length so doesn't need to be longer
retractor and protractor muscles on forelimb roughly the same size, because for holding up body weight, not producing lots of power (done with hindlimbs), because harder to have strong forelimb attachment to body, lungs and ribcage in the way
51
Turbinals
warm and humidify air before going into lungs to reduce stress on alveoli (maxilla turbinals)
increase surface area of olfactory epithelium (ethmo and nasoturbinals)
evidence in Therocephalians- ridges in nose
better evidence in advanced cynodonts eg. Brasilitherium- thin sheets of ossified bone
52
Early evidence of lactation
eg. in morganucodontids
deterministic growth evolves in cynodonts, evidence of juveniles same size as adults, therefore grown quickly
if lactating, dental eruption will be delayed until weaning, meaning there is a reduced time in which teeth of intermediate size are needed, and so a reduced number of dental replacements
because deterministic, growth is truncated in adult stages, meaning that jaw length limited, also means fewer dental replacements.
amyloblast activity is correlated with osteoblast, so reduced skeletal growth means reduced tooth growth. Reduced enamel extension rates (measured in striae of Retzius) => 4.8 micrometres a day vs 86 in cynodonts (because less frequent tooth replacements).
Means mammaliaforms are diphyodont (evidence of teeth embedded in crypts), and there is reduced variability in the relative positions of upper and lower molars. Allows complex occulsuion, tribospheny in mammal crown.
Permanent dentition in adult means need to guard against crack propagation, have prismatic enamel (bundles of crystallines surrounded by interprismatic enamel)
these along with the precise mammalian jaw musculature allows mammals to access more diets on evolutionary timescale
53
Characteristics of endothermy
High basal metabolic rate
High body temperature (28 to 42)
Constant body temp (+/- 2)
High maximum aerobic activity level
54
Advantages of endothermy
Active in wider range of ambient temperatures and at night
More complex organism (enzymes, nerve cells remain better integrates/working more efficiently)
More rapid development of young
Greater foraging potential, mate seeking etc
55
Correlated progression model
(Kemp, 2006)?
different functions all related to each other, each can't evolve too far without other elements also evolving
eg link of changing circulation, changing teeth and jaw musculature, more precise kidney tubules, increased insulation, add diaphragm
problem of integration vs evolvability
strength of the integration may vary over time
functional linkages are flexible enough to allow small changes without loss of fitness
selection acts on overall fitness of organism, not individual characters
lines of arguments for model=
mammal structures and functions are connected
synaspsia Hennigian ladder (fossil record)- characters change between fossils, pattern of acquisition as expected by model
56
Drivers for mammals to evolve
following ridge in adaptive landscape
adaptation for active lifestyle under increasing range of ambient temperatures and humidity
locomotion effective in heterogenous environment
increasingly complex CNS leads to more adaptable behaviour
evolve to become more independent of external environment, homeostasis
