week 4

Question 1

What are 5 key developments in therapsids?

Answer 1

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

Question 2

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

Answer 2

more muscle development, muscle specialisation, and bulging of muscles

Question 3

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

Answer 3

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.

Question 4

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

Answer 4

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.

Question 5

What is the most advanced of the Pelycosaurs?

Answer 5

Sphenacodontia

Considered the closest outgroup among the pelycosaurs before the Therapsids appear

Question 6

Being endothermic is energetically expensive, give some figures

Answer 6

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.

Question 7

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

Answer 7

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.

Question 8

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

Answer 8

Tetraceratops

Question 9

What is the most basal group of the Therapsids?

Answer 9

Biarmosuchia

Primitive features when looking at the evolution of mammals

Question 10

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

Answer 10

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

Question 11

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

Answer 11

90

Question 12

An example of a fossil from the sub order Therocephalia?

Answer 12

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

Question 13

Example of a fossil from the sub order Gorgonopsia?

Answer 13

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

Question 14

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

Answer 14

therapsids

Question 15

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

Answer 15

skull
teeth
limbs
physiology

Question 16

What severely reduced the diversity of therapsids?

Answer 16

mass extinction at the end of the permian

Question 17

After the pelycosaurs came the ____ and after came the ____

Answer 17

therapsids

cynodonts

Question 18

what are the cynodonts?

Answer 18

they are the more advanced therapsids

their own suborder

Question 19

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

Answer 19

decrease

Question 20

What is the classic cynodont fossil?

Answer 20

Thrinaxodon

Question 21

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

Answer 21

the middle ear

Question 22

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

Answer 22

dentary
angular
articulate and quadrate (QA jaw joint)
stapes

Question 23

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

Answer 23

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

Question 24

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

Answer 24

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

Question 25

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

Answer 25

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

Question 26

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

Answer 26

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

Question 27

What skeletal developmental changes occur in the cynodonts?

Answer 27

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

Question 28

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

Answer 28

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

Question 29

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

Answer 29

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

Question 30

How does the posture change in Cynodonts?

Answer 30

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

Question 31

what are synapomorphies?

Answer 31

shared derived characteristics

Question 32

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

Answer 32

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

Question 33

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

Answer 33

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

Question 34

What are the atlas and the axis?

Answer 34

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

Question 35

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

Answer 35

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

Question 36

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

Answer 36

biggest 75 96

Question 37

what is the current hypothesis on the end permian extinction?

Answer 37

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

Question 38

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

Answer 38

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

Question 39

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

Answer 39

dicynodontia | lystrosaurus - suborder dicynodontia

Question 40

Which time periods are included in the mesozoic?

Answer 40

triassic jurassic cretaceous

Question 41

What 2 things define the triassic?

Answer 41

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

Question 42

What 2 things define jurassic?

Answer 42

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

Question 43

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

Answer 43

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

Question 44

What was the Mesozoic climate like? (3)

Answer 44

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

Question 45

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?

Answer 45

herbivorous dicynodonts (synapsids) and archosaurs (diapsids) dominated vegetation included modern gymnosperms but no angiosperms yet

Question 46

what is generally accepted as the first early dinosaur?

Answer 46

Eoraptor

Question 47

which synapomorphy characterises node B [Thrinaxodontidae]?

Answer 47

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

Question 48

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

Answer 48

thrinaxodon

Question 49

in a lizard what is the palate formation like?

Answer 49

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

Question 50

what occurs during the cynodonts to palate formation?

Answer 50

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)

Question 51

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

Answer 51

secondary palate formation

Question 52

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

Answer 52

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

Question 53

what is characteristic synapomorphy of node C [eucynodontia]?

Answer 53

dentary is getting larger and approaching the QA joint | cheek teeth are in deep sockets - this is a change not quite yet molars

Question 54

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

Answer 54

90%

Question 55

Cynognathus also has more complex ___ of thier teeth

Answer 55

occlussion | allowing for more efficient chewing of food

Question 56

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

Answer 56

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

Question 57

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

Answer 57

Traversondotidae africa and south america diaphragm breathing

Question 58

what is considered the close out group of mammals?

Answer 58

Tritylodontidae

Question 59

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

Answer 59

cynodonts | skull, jaw, teeth, and post cranial skeleton

Question 60

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

Answer 60

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

Question 61

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

Answer 61

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

Question 62

was there convergent evolution in the middle ear?

Answer 62

yes 3 times

Question 63

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

Answer 63

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

Question 64

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

Answer 64

tribosphenic molar

Question 65

how does the tribosphenic molar evolve?

Answer 65

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

Question 66

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

Answer 66

Tribosphenida

Question 67

Evidence suggests that the Tribosphenida were a radiation in the ____

Answer 67

northern hemisphere

Question 68

Tribosphenic molars have become modified in many derived taxa why?

Answer 68

as diet changes

Question 69

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

Answer 69

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

Question 70

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

Answer 70

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

Question 71

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

Answer 71

some primitive and some advanced characteristics