The amniotes inc. the chelonians

Question 1

What groups does amniota include?

Answer 1

Reptiles, birds and mammals. Everything except fish and amphibians.

Question 2

Why was the evolution of the amniotic egg so important in the history of life?

Answer 2

It allowed independence from the water.

Question 3

There are a series of membranes around the embryo that make up the amniotic egg. What are they?

Answer 3

1. Yolk sac
2. Amniotic membrane
3. Chorion
4. Allantois

Question 4

What does the yolk sac do?

Answer 4

Blood vessels originate here so the foetus can access the yolk proteins. Is formed from endoderm.

Question 5

What does the amniotic membrane do?

Answer 5

Encapsulates fluid around the embryo to cushion it.

Question 6

What does the chorion do?

Answer 6

It lines the inside of the egg and acts as an interface with the shell. Pores enable gas exchange.

Question 7

What germ layer is the chorion made from?

Answer 7

Ecto and mesoderm.

Question 8

What does the allantois do?

Answer 8

Stores nitrogenous waste from metabolism.

Question 9

What germ layer is the allantois made from?

Answer 9

Mesoderm.

Question 10

What happens to the allantois as development progresses?

Answer 10

It grows as it accumulates more waste and develops its on blood vessels so its large surface area can contribute to gaseous exchange.

Question 11

What is the shell made from?

Answer 11

CaCl3 (calcium carbonate). The hardness of a shell relies on varying calcium carbonate compositions.

Question 12

Give 3 reasons why fossilised eggs are not helpful in identifying amniotes.

Answer 12

1. Mammals do not lay eggs
2. Eggs are not well preserved
3. It is rare to find foetal fossils within eggs

Question 13

Give 3 major osteological traits that united the amniotes.

Answer 13

1) An ossified supraoccipital
2) Transverse flange of the pterygoid
3) Ankle containing an astragalus and calcaneum bone

Question 14

Define an ‘ossified supraoccipital’.

Answer 14

A single bone down the midline of the skull.

Question 15

Define the ‘transverse flange of the pterygoid’.

Answer 15

Plate of bone that projects down from the palate for jaw-closing muscle attachment.

Question 16

Give the 3 main amniote groups that emerged in the late Carboniferous/early Permian.

Answer 16

1. Synapsids
2. Parareptiles
3. Diapsids

Question 17

What is a synapsid?

Answer 17

‘Mammal-like reptiles’ that had large sails down their spine. Had single temporal fenestrae.

Question 18

What was the sail for in synapsids?

Answer 18

Thermoregulation, early synapsids were not warm-blooded.

Question 19

What extant group descended from the synapsids?

Answer 19

The mammals.

Question 20

The parareptiles are now completely extinct. True or false?

Answer 20

True, although it is believed that turtles may have descended from them, in which case the answer would be false.

Question 21

An example of a parareptile group are the mesosaurs. What were they like?

Answer 21

Small, aquatic animals. Had sharp teeth for eating fish. Heavy ribs to control buoyancy as were too light.

Question 22

An example of a parareptile group are the millerosaurs. What were they like?

Answer 22

Insectivorous animals from South America. Showed the first evidence for the impedance-matching ear in amniotes.

Question 23

An example of a parareptile group are the procolophonids. What were they like?

Answer 23

Similar to the millerosaurs, were insectivorous with impedance-matching ears.

Question 24

An example of a parareptile group are the pareiasaurs. What were they like?

Answer 24

Large, heavily armoured organisms. Possessed broad, ‘leaf-shaped’ teeth, indicating herbivory.

Question 25

Herbivory is a trait that evolved in the amniotes. True or false?

Answer 25

True.

Question 26

What extant groups descended from the diapsids?

Answer 26

The reptiles and birds.

Question 27

What is a diapsid skull condition?

Answer 27

Has 2 temporal fenestrae separated by an upper and lower temporal bar.

Question 28

What is the anapsid skull condition?

Answer 28

No temporal fenestrae.

Question 29

How are chelonians able to stop breathing for lung periods of time?

Answer 29

They have lung ventilation with locomotion.

Question 30

When and where was odontochelys from?

Answer 30

The middle Triassic of China.

Question 31

What did odontochelys look like?

Answer 31

Had a long neck and tail, v. well developed plastron but poorly formed carapace. Only displayed rib extension/expansion.

Question 32

When and where was proganochelys from?

Answer 32

The late Triassic of Germany.

Question 33

What did proganochelys look like?

Answer 33

Fully formed shell, teeth and a long bony tail. Was unable to retract head into body.

Question 34

Give the 2 theories for the origin of turtles.

Answer 34

1. Turtles as parareptiles: turtles evolved from pareaisaurs whose bondy scutes/armour developed into a shell.
2. Turtles as diapsids: turtles are closely related to archosaurs.

Question 35

How does the existence of odontochelys contest the ‘turtles as parareptiles’ theory?

Answer 35

Odontochelys’ shell showed it developed plastron-first, thus it could not have been formed from the dermal armour or pareaisaurs.

Question 36

Give support for the ‘turtles as diapsids’ theory. List 3 reasons.

Answer 36

1. Eunotosaurus, an archosaur from the Permian, very closely resembles modern chelonians
2. All archosaurs lay eggs, it is an evolutionary constraint. Even fully aquatic marine species of turtle still return to land to lay eggs.
3. There is molecular evidence