Lepidosauria Flashcards
Amniota: animals with an amniote egg, adaptations for land; divided into the Sauropsida and Synapsida
Sauropsida
division 1
Archosauria
Lepidosauria
division 2
Tuataras (Rhynchocephalia)
Lizards and Snakes (Squamata)
…
Summary
Amniota:
animals with an amniote egg, adaptations for land;
divided into the Sauropsida and Synapsida
Summary
division of sauropsida
Archosauria
Lepidosauria
Summary
division of lepidosauria
Tuataras (Rhynchocephalia)
Lizards and Snakes (Squamata)
What is a reptile
3 points
- All tetrapods whose ancestors had an amniote egg
Excludes the Lissamphians
Includes the mammals and birds
- Amniota
Allow fertilised eggs to be laid on land
2 lineages
Synapsida
Sauropsida [focus of this deck]
- Not a taxonomic rank
Paraphyletic or polyphyletic, depending on definition - Usually equates to Amniota
Amniota
2 points
- Evolved from the amphibian reptilomorphs about 312 Mya
- The amniote egg
Extra-embryonic membranes: amnion, chorion, allantois
water-tight
allows gas exchange
copes with nitrogenous waste
Sauropsida 3 points
- One of two amniote radiations (the other is the Synapsida)
- All amniotes descended from the last common ancestor of extent reptiles and birds
- Lack a clearer definition based on morphology
Sauropsida [divides into]
Parareptilia
Diapsida [divides into]
Lepidosauromorpha
Archosauromorpha
Diapsida
Lepidosauromorpha
- Sprawling gait
Trunk and tail have sinusoidal movement
- Sliding “joint” in shoulder
- Pleurodont dentition
Sides fused to inner surface of jaw bone - Hemipenis
- Scales are keratinised structures of epidemis
overlapping
shed collectively - Caudal autotomy
Diapsida
Archosauromorpha
- Parasagittal gait
Limbs parallel to vertebral column - Reduction / loss of sternum
- Thecodont dentition
Teeth in sockets - Penis
- Scutes made of dermis,
may have bony component
Non-overlapping
shed in flakes - Cannot shed tails
Ichthyopterygia
[division from lepidosauromorpha]
5 points
1/ Extinct taxon of aquatic lepidosauromorphs, dating from approx. 250 Mya
- Terrestrial ancestor that probably hunted in shallow water
- Later forms adapted for deep diving
- Large eyes, stiff trunk
- Live young, may have been warm-blooded
What is a lepidosaur
3 points
- A sauropsid amniote
- Only living members of the Lepidosauromorpha
- Modern tuatara, snakes, lizards
lepidosaur
Body Plan
- Ancestor was lizard-like
- Dry scaly skin with few dermal glands
Shedding mechanisms - Paired hemipenes in eversible pouches
- Hooked fifth metatarsal
Like a mammalian heel - Fracture planes in tail vertebrae for caudal autotomy
lepidosaur
Respiration
- Lungs lack bronchioles
Simple hollow sacs with internal folds
Large lizards have interconnected chambers
Snakes have one working lung
- No diaphragm
lepidosaur
Circulation
- Three-chambered heart
Two atria, one ventricle
Partial mixing of oxygenated and deoxygenated blood
lepidosaur
Digestion
2 points
- Simple, J-shaped stomach
- Temperature affects speed of digestion
May not eat for months
lepidosaur
2 points
- Excrete uric acid with some ammonia and urea
Uric acid secreted rather than filtered - Snakes have one kidney
lepidosaur
Nervous system
3 points
- Brain < 1% of body mass
- Expanded cerebrum and cerebellum compared to amphibians
- Spinal cord extends to tip of tail
lepidosaur
Senses
3 points
- Vary according to dominant sense
- Vomeronasal organ
airbourne molecules transferred to Jacobson’s organ
- Usually poor hearing
lepidosaur
Reproduction
3 points
- Sexual selection
- Males have hemipenes, usually inverted within their bodies
Use one at a time, alternate - Oviparous, viviparous and ovoviviparous species
- Parthenogenesis
Rhynchocephalia
[division from lepidosaurmorpha]
(Sister-group to lizards and snakes)
4 points
- Pineal eye
- Acrodont teeth (fused to jaw bone)
Two parallel rows of teeth in upper jaw
Overhanging, incisor-like teeth
- Gastralia (ventral ribs, lost in squamates)
- Rich history in Mesozoic Era, now only 1 species
The tuatara Sphenodon punctatus
Squamata
[division from lepidosaurmorpha]
3 points
- Kinetic (mobile) quadrate bone in skull
- Permits swallowing or large prey items
- Generalists have uniform teeth
Heterogeneous teeth
Highly specialised teeth of snakes
Squamata: Gekkota
2 points
- Geckos
Long tails (equal to body length)
Often nocturnal
Adhesive toe pads in some arboreal species
- Australasian legless lizards
No pectoral skeleton
Vestigial hindlimbs and pelvic
girdle
Diurnal
Squamata: Scincomorpha
2 point
- Skinks
No pronounced neck
Relatively small legs (some are legless)
Digging / burrowing adaptations
Carnivorous / insectivorous
- Girdled lizards
Squamata: Lacertoidea
3 points
- “True” lizards
Slender bodies and long tails - Whiptails and tegus
Large rectangular scales ventrally, granular scales dorsally
Forked tongue
Some species wholly female
- Amphisbaenians or worm lizards
Burrowing mode of life
All species are limbless except for Bipes
Rings of scales
Squamata: Toxicofera
- Forked tongue
- Venom
Molecular evidence for an early evolution of venom (200 Mya)
Originally for digestion of plants?
