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Mammals and evolution > week 4 > Flashcards

week 4 Flashcards

1
Q

What are 5 key developments in therapsids?

A

Gait and locomotion - more upright posture, elbows back and knees forwards

Increased size of temporal fenestra

Teeth become more differentiated

jaw joint becomes more mammal-like

secondary palate develops in later forms

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2
Q

In the synapsid lineage as the temporal fenestra gets larger what does it allow for?

A

more muscle development, muscle specialisation, and bulging of muscles

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3
Q

In the synapsid lineage apart from the temporal fenestra what else gradually change?

A

Collectively teeth become more differentiated and jaw joint changes gives much more scope for adaptation, in terms of feeding, food processing, chewing, which becomes important as endothermy also evolves.

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4
Q

In the synapsid lineage the middle ear develops as the jaw develops and also the ____ ___evolves

A

secondary palate

important as it allows feeding and breathing at the same time. This is important as energy requirements increase due to the acquisition of endothermy.

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5
Q

What is the most advanced of the Pelycosaurs?

A

Sphenacodontia

Considered the closest outgroup among the pelycosaurs before the Therapsids appear

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6
Q

Being endothermic is energetically expensive, give some figures

A

in the cold a mammals uses 100 fold more energy than an ectotherm, even in a more temperate climate we are looking at 30 fold more energy required in endotherm than ectotherm.

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7
Q

What makes Dimetrodon one of the more advanced Pelycosaurs? And what is the significance?

A

reflected laminar of the angular bone in the jaw

a popular hypothesis is this may have been the beginnings of a primitive ear because later on this is where the ear drum will be supported by the angular bone.

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8
Q

The link between the Pelycosaurs and Therapsids isnt very clear but what is generally accepted to be the closest outgroup of the Therapsids?

A

Tetraceratops

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9
Q

What is the most basal group of the Therapsids?

A

Biarmosuchia

Primitive features when looking at the evolution of mammals

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10
Q

Dinocephalia are another group of the Therapsids, they are more advanced, what is the well known fossil?

A

Moschops
large animal - the limbs and the gait beginning of rear limbs becoming tucked under the body 0 famous for bony domed skull thought to be used in combat – herbivores

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11
Q

The sub order Dinocephalia is very numerous in number of species, estimated that they make up ___% of the therapsid fauna of south africa

A

90

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12
Q

An example of a fossil from the sub order Therocephalia?

A

Eiciolacerta
dentary bone in the lower jaw is getting larger, it is beginning to form the majority of the lower jaw and other elements of the bony jaw are getting smaller – south African

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13
Q

Example of a fossil from the sub order Gorgonopsia?

A

Lycaenops
predator – top carnivore of the time – elongated skull – hard bite – note the sprawling gait at the front and more upright rear limbs – more advanced and primitive limb girdle structure makes it hard to get around

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14
Q

Early radiations of pelycosaurs gave way to more advanced _____ in the mid to late permian

A

therapsids

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15
Q

A good fossil record shows the gradual acquisition of increasingly mammal like traits such as….(4)

A

skull
teeth
limbs
physiology

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16
Q

What severely reduced the diversity of therapsids?

A

mass extinction at the end of the permian

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17
Q

After the pelycosaurs came the ____ and after came the ____

A

therapsids

cynodonts

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18
Q

what are the cynodonts?

A

they are the more advanced therapsids

their own suborder

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19
Q

As the therapsids become more advanced what happens to their size?

A

decrease

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20
Q

What is the classic cynodont fossil?

A

Thrinaxodon

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21
Q

As we move from primitive to advanced cynodonts we see an amazing transition in which organ?

A

the middle ear

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22
Q

In the early mammal like reptile what were the 5 important parts of the middle ear?

A

dentary
angular
articulate and quadrate (QA jaw joint)
stapes

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23
Q

What forms the primitive ear in the early mammal like reptiles and how did this function?

A 
the stapes (stirrup bone) forms the primitive ear.
It is floating around bracing parts of the skull the quadrate and the otic capsule.
There is some hearing going on where vibrations through the jaw and skull are transmitted by the stapes
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24
Q

What happens to the middle ear in the mammal which bones form what?

A 
Quadrate = incus
Angular = tympanic ring
articulate = malleus
dentary = forms whole jaw joint and only bone in the lower jaw
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25
Q

So the end function of the angular bone in the middle ear of mammals is what?

A

tympanic ring structure which supports the ear drum to which then hinges on to the 3 middle ear bones to form the inner ear

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26
Q

What happens to the bones in the lower jaw as we progress through mammalian evolution?

A

the dentary gets larger and the quadrate, angular and articulate get smaller

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27
Q

What skeletal developmental changes occur in the cynodonts?

A

changes in the gait and a reduction of ribs in the lumbar region

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28
Q

explain further the reduction of ribs that occur in the cynodonts.

A

As we get a muscular diaphragm, the sheet muscle separating the chest and abdominal cavity, this ties in with the loss of the ribs. As the muscular diaphragm is evolving as more efficient respiration is required to support the extra energy required for endothermy

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29
Q

How can we infer the reduction of ribs is to do with the muscular diaphragm? problem?

A

the diaphragm isnt going to fossilise very well but we can infer the evolution of the diaphragm from the reduction of ribs seen in Thrinaxodon

30
Q

How does the posture change in Cynodonts?

A

it goes from the limbs being horizontal and sticking out from the shoulder girdle to beocming more upright and erect like that seen in current extant mammals

31
Q

what are synapomorphies?

A

shared derived characteristics

32
Q

Node A in the phylogeny [procrynosuchidae] is defined by which 3 synapomorphies?

A

double occipital condyle
presence of flared zygomatic arch
dentry bone 75% of lower jaw

33
Q

Procrynosuchas shows a number of advancements over earlier forms such as therocephalians, including ? (7)

A

external adductor muscle is now more specialised and has split into a temporalis and a masseter

the dentary bone is enlarged

forelimbs are akimbo, double gait at rear

the beginnings of a secondary palate separate the nasal cavity from the mouth so breathing and chewing / eating are separate

vertebral column increased rigidity produced by the interlocking zygopophyses

greater degree of head movement as the cervical form an atlas and axis

double occipital condyle is present on the skull which forms the joint / articulation with the atlas

34
Q

What are the atlas and the axis?

A

they are modified spinal vertebrae that allow the nodding and shaking of the head

35
Q

At the end of the permian there was an extinction and what can you see?

A

some cynodonts were around but there is quite a clear line dividing the permian and triassic where there are major shifts in biodiversity. Dicynodontia sub order survived through

36
Q

The end permian extinction was the ___ of the big 5.
___% of terrestrial vertebrates went extinct
___% of marine species went extinct

A

biggest
75
96

37
Q

what is the current hypothesis on the end permian extinction?

A

2 large volcanic events
massive out pourings of lava forming siberian and emeishan traps
huge impact on the climate

38
Q

what climate effects are thought to have taken place during the end permian extinction?

A

vulcanism causes:

  • -temperature increases
  • -runaway green house effect
  • -huge rise in methane
    • lack of oxygen in the oceans
  • -acid rain kills vegetation
  • -soil runs off into the sea
39
Q

which primitive therapsids made it through the end permian extinction?and after the extinction over 50% of land animals are what?

A

dicynodontia

lystrosaurus - suborder dicynodontia

40
Q

Which time periods are included in the mesozoic?

A

triassic
jurassic
cretaceous

41
Q

What 2 things define the triassic?

A

after a slow recovery mammal like reptiles, the cynodonts, will be around but ultimately take second place to the large adaptive radiation of the dinosaurs

Pangea is at maximum coalescence but now the opposite trend occurs in the mesozoic and pangea gradually breaks up and the continents separate to form a geography similar to that now

42
Q

What 2 things define jurassic?

A

gondwana is separating off again from laurasia in the north

the separated continents are isolating different groups of vertebrates and different evolutionary scenarios occur on these different land masses as there is no gene flow between them

43
Q

what is the key thing about the late cretaceous in terms of for our extant mammals?

A

key time for the evolution of extant orders of mammals.
During this time the main lineages are formed and evolving separately. Periodically there are connections between the various land masses and we can use this to understand marsupials, monotremes, and some of our eutherian super orders

44
Q

What was the Mesozoic climate like? (3)

A

weather more stable
no polar ice caps
higher latitudes moist and lower latitudes / equatorial regions dry

45
Q

During the early Triassic period the permian extinction initially left an impoverished terrestrial fauna and early on what dominated (2), what was the vegetation like?

A

herbivorous dicynodonts (synapsids) and archosaurs (diapsids) dominated

vegetation included modern gymnosperms but no angiosperms yet

46
Q

what is generally accepted as the first early dinosaur?

A

Eoraptor

47
Q

which synapomorphy characterises node B [Thrinaxodontidae]?

A

lower jaw coronoid process
that is the bone on the dentary that extends up through the zygonapomarge and pokes up providing a large surface area for muscle attachment

48
Q

The secondary palate formation is beginning to get larger in the ___

A

thrinaxodon

49
Q

in a lizard what is the palate formation like?

A

there is no separation between the nasal cavity and the mouth, this makes it difficult to eat and breath at the same time

50
Q

what occurs during the cynodonts to palate formation?

A

a secondary hard palate is starting to form which separates the nasal chamber and the mouth, air can be directed through the nasal passage into the lungs so chewing and breathing can occur at the same time (mammals have secondary palate)

51
Q

what is an important incremental change as cynodonts get more efficient food processing due to the requirements of extra energy for endothermy?

A

secondary palate formation

52
Q

secondary palate formation also allows what else to help with increase respiration efficiency?

A

allow specialisation of the nasal chamber with very fine turbanate bones. the nose of mammals is full of fine bones that act as a high surface area for the nasal epithelium to be carried on which can help to heat up incoming air and act as a heat exchange and also sense of smell

53
Q

what is characteristic synapomorphy of node C [eucynodontia]?

A

dentary is getting larger and approaching the QA joint

cheek teeth are in deep sockets - this is a change not quite yet molars

54
Q

Cynognathus is a more advanced cynodont and how much of the dentary is the lower jaw?

A

90%

55
Q

Cynognathus also has more complex ___ of thier teeth

A

occlussion

allowing for more efficient chewing of food

56
Q

Probainognathus is a late therapsid (mammal like reptile) from the mid triassic, what is special about this fossil and others of this time?

A

it has such a large dentary bone in the lower jaw and the other lower jaw bones have got very small. This is an intermediate form
you have the ancestral jaw joint Q/A plus a secondary jaw joint squamosal. the 2 jaw joints are an intermediate between the ancestral and extant form.
functional continuity as features and traits are evolving everything else has to keep working so during the transitio to the formation of the middle ear from the jaw joint bones you have to maintain th eworking jaw joinnt

57
Q

Middle triassic cynodonts:
Massetognathus
The _____ were the most successful group of herbivorous cynodonts
Best known from the middle Triassic of ___ and ____
Reduction of lumbar ribs is an indication of the development of the ___ allowing for improvement in ___ efficiency

A

Traversondotidae
africa and south america
diaphragm
breathing

58
Q

what is considered the close out group of mammals?

A

Tritylodontidae

59
Q

Following the permian extinction, advanced therapsids of the triassic (___) show increasingly mammal like characteristics, these include changes to the __, __, __ and ____

A

cynodonts

skull, jaw, teeth, and post cranial skeleton

60
Q

at the end of the triassic there was another extinction as pangea breaks up, what caused this extinction and what were the consequences?

A

volcanism
super green house effect
Theropod dinosaurs abruptly increased in size and relative abundance during this time
Age of the dinosaurs begin

61
Q

What was the ecosystem like in the jurassic / cretaceous period?

A

a major turnover in terrestrial vertebrates occurred
mammal like reptiles were replaced as dominant land vertebrates by reptiles (Dinosaurs)
lizards, modern amphibians and early birds appear
the conifer and fern dominated vegetation of the late triassic continued into the jurassic

62
Q

was there convergent evolution in the middle ear?

A

yes 3 times

63
Q

what is an example of ontogeny reflecting phylogeny in the middle ear?

A

if you look at the foetus of the opossum you can see during the development that the structures run through a similar arrangement to that you see in the mammal like reptiles

64
Q

another significant development in mammalian evolution is the development of ___ teeth?

A

tribosphenic molar

65
Q

how does the tribosphenic molar evolve?

A

in earlier mammals there are 3 cusps on the teeth and in more advanced mammals the 3 cusps have shifted slighlty so they are not in line but more like a pesel and mortar to allow for more efficient grinding

66
Q

Mammals that have tribosphenic molars form a clade traditionally called the _____

A

Tribosphenida

67
Q

Evidence suggests that the Tribosphenida were a radiation in the ____

A

northern hemisphere

68
Q

Tribosphenic molars have become modified in many derived taxa why?

A

as diet changes

69
Q

what does the evolution of the tribosphenic molar mean in terms of teeth replacement and energy intake?

A

It can increase energy intake and efficiency of getting energy out of food due to the grinding system

Means you cant be continually replacing teeth. Teeth are continually replaced in the early mammal like reptiles, but now we only have 2 sets of teeth (milk and adult), because the complex occlussion pattern evolves you have to reduce the number of teeth

70
Q

How do you define a mammal? when can you say the first mammal occurred?

A

this depends on your definition of a mammal. There are 2 ways of defining a mammal:

  • —-everything from Morganucodont onwards including mammaliaformes
  • ——everything from the crown group mammalia - this means everything extant mammals and all of the relatives - so basically monotremes onwards
71
Q

The crown group mammalia includes some extinct lineages that don’t really have all the characteristics of the modern mammal.

A

some primitive and some advanced characteristics

Mammals and evolution (6 decks)

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