Diapsids: the lepidosaurs Flashcards
List 5 synapomorphies of lepidosaurs.
- Skin shedding
- Palatal teeth
- Caudal autotomy
- Fused astragalo-calcaneum and enlarged metatarsal joint
- Hooked fifth metatarsal
- Epiphyses
Define caudal autotomy.
The tail has a fracture plane that allows it to be detached, e.g. for predator evasion.
When the tail is regrown it is the same as the original. True or false?
False: the original was muscle and bone, the new one is a simpler tissue that is less energy expensive to grow
What are epiphyses?
Extra ossification centres formed when bones grow to meet each other.
What 2 groups are the lepidosaurs split into?
- Squamata
2. Rhynchocephalia
The squamates contain which animals?
Lizards, snakes and amphisbaenids.
There are 6 groups within the squamata. What are they?
- Iguania
- Gekkota
- Scincomorpha
- Anguimorpha
- Serpentes
- Amphisbaenids
What is characteristic about the scinocomorphs?
They are ovivivaporous, meaning live young hatch from eggs inside the mother.
What famous group does the anguimorpha contain?
The varanid (monitor) lizards
The anguimorpha contains the only poisonous lizard. What is it?
The Gila Monster.
What are amphiabaenids?
Fossorial animals, many species are limbless. Have small, bullet-shaped heads for burrowing.
Give 4 synapomorphies of the squamates.
- Cranial kinesis
- Absence of lower temporal bar
- Pleurodont teeth
- Paired hemipenes
Explain cranial kinesis.
There are extra hinges and loose points in the skull that allow flexibility and movement of the bones.
What 2 advantages does cranial kinesis give the squamates?
- Colonisation of new ecological niches due to novel feeding strategies
- Shock absorption
Why is the lower temporal bar missing in squamates?
Due to cranial kinesis.
Describe the cranial kinesis of snakes.
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.
What are pleurodont teeth?
Teeth that are attached by their sides to the inner edge of the jaw bone.
There is dispute as to which squamate group is the oldest. What does the molecular data suggest?
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.
Rhynchocephalia is the second lepidosaur group. How many members does it have?
Only one extant member: sphenodon or the tuatara.
Where is sphenodon found?
On an island off the coast of New Zealand.
List 4 unique characters of sphenodon.
- Enlarged dentary bone
- Acrodont teeth
- Enlarged palatine tooth row
- Lower temporal bar
Define acrodont teeth.
The tooth base is fused to the jaw bone and does not have roots. Thus tooth replacement is very slow.
Which 2 lepidosaurs do not display cranial kinesis?
- Amphisbaenids due to fossorial lifestyle
2. The rhynchocephalians (sphenodon). Perhaps why they possess lower temporal bar.
The fossil record for lepidosaurs is incomplete. Why?
Specimens are often small and easily broken.
Give 2 ‘stem lepidosaur’ fossil specimens.
- Kuehneosaurs: gliding animals with splayed ribs
2. Sophineta
Major diversification of diapsids occurred in which time period?
Late Triassic
Large marine mosasaurs are thought to be related to which squamate group?
Anguimorpha
Define opportunistic replacement.
External factors cause one group to decline, leaving empty niches available for colonisation by other species.
Explain how opportunistic replacement has shaped present lepidosaur diversity.
Rhynchocephalia was previously pan-global, but were outcompeted by the squamates.
In which time period was rhynchocephalia globally distributed?
Late Triassic
When did the rhynchocephalians begin to decline?
The cretaceous
