Diapsids: the lepidosaurs

Question 1

List 5 synapomorphies of lepidosaurs.

Answer 1

1. Skin shedding
2. Palatal teeth
3. Caudal autotomy
4. Fused astragalo-calcaneum and enlarged metatarsal joint
5. Hooked fifth metatarsal
6. Epiphyses

Question 2

Define caudal autotomy.

Answer 2

The tail has a fracture plane that allows it to be detached, e.g. for predator evasion.

Question 3

When the tail is regrown it is the same as the original. True or false?

Answer 3

False: the original was muscle and bone, the new one is a simpler tissue that is less energy expensive to grow

Question 4

What are epiphyses?

Answer 4

Extra ossification centres formed when bones grow to meet each other.

Question 5

What 2 groups are the lepidosaurs split into?

Answer 5

1. Squamata

2. Rhynchocephalia

Question 6

The squamates contain which animals?

Answer 6

Lizards, snakes and amphisbaenids.

Question 7

There are 6 groups within the squamata. What are they?

Answer 7

1. Iguania
2. Gekkota
3. Scincomorpha
4. Anguimorpha
5. Serpentes
6. Amphisbaenids

Question 8

What is characteristic about the scinocomorphs?

Answer 8

They are ovivivaporous, meaning live young hatch from eggs inside the mother.

Question 9

What famous group does the anguimorpha contain?

Answer 9

The varanid (monitor) lizards

Question 10

The anguimorpha contains the only poisonous lizard. What is it?

Answer 10

The Gila Monster.

Question 11

What are amphiabaenids?

Answer 11

Fossorial animals, many species are limbless. Have small, bullet-shaped heads for burrowing.

Question 12

Give 4 synapomorphies of the squamates.

Answer 12

1. Cranial kinesis
2. Absence of lower temporal bar
3. Pleurodont teeth
4. Paired hemipenes

Question 13

Explain cranial kinesis.

Answer 13

There are extra hinges and loose points in the skull that allow flexibility and movement of the bones.

Question 14

What 2 advantages does cranial kinesis give the squamates?

Answer 14

1. Colonisation of new ecological niches due to novel feeding strategies
2. Shock absorption

Question 15

Why is the lower temporal bar missing in squamates?

Answer 15

Due to cranial kinesis.

Question 16

Describe the cranial kinesis of snakes.

Answer 16

Most extreme kinesis of all the squamate groups. The lower jaw and skull are not joined by bone, instead are joined by ligaments. The lower jaw is also split in two and joined by ligaments.

Question 17

What are pleurodont teeth?

Answer 17

Teeth that are attached by their sides to the inner edge of the jaw bone.

Question 18

There is dispute as to which squamate group is the oldest. What does the molecular data suggest?

Answer 18

Gekkota is the oldest, then the skinks and amphibaenids, them the iguanians and anguimorphs. The serpents are thought to have branched off from the iguanians.

Question 19

Rhynchocephalia is the second lepidosaur group. How many members does it have?

Answer 19

Only one extant member: sphenodon or the tuatara.

Question 20

Where is sphenodon found?

Answer 20

On an island off the coast of New Zealand.

Question 21

List 4 unique characters of sphenodon.

Answer 21

1. Enlarged dentary bone
2. Acrodont teeth
3. Enlarged palatine tooth row
4. Lower temporal bar

Question 22

Define acrodont teeth.

Answer 22

The tooth base is fused to the jaw bone and does not have roots. Thus tooth replacement is very slow.

Question 23

Which 2 lepidosaurs do not display cranial kinesis?

Answer 23

1. Amphisbaenids due to fossorial lifestyle

2. The rhynchocephalians (sphenodon). Perhaps why they possess lower temporal bar.

Question 24

The fossil record for lepidosaurs is incomplete. Why?

Answer 24

Specimens are often small and easily broken.

Question 25

Give 2 ‘stem lepidosaur’ fossil specimens.

Answer 25

1. Kuehneosaurs: gliding animals with splayed ribs

2. Sophineta

Question 26

Major diversification of diapsids occurred in which time period?

Answer 26

Late Triassic

Question 27

Large marine mosasaurs are thought to be related to which squamate group?

Answer 27

Anguimorpha

Question 28

Define opportunistic replacement.

Answer 28

External factors cause one group to decline, leaving empty niches available for colonisation by other species.

Question 29

Explain how opportunistic replacement has shaped present lepidosaur diversity.

Answer 29

Rhynchocephalia was previously pan-global, but were outcompeted by the squamates.

Question 30

In which time period was rhynchocephalia globally distributed?

Answer 30

Late Triassic

Question 31

When did the rhynchocephalians begin to decline?

Answer 31

The cretaceous