Rise of Aminotes and Biology of Squamates Flashcards
What defines an aminote
Amniotes are tetrapods that possess an amniotic egg. This evolutionary innovation allows reproduction on land without water
What are three major derived features shared by all crown group amniotes
Internal fertilisation
Keratinised integument and integumentary appendages
Negative pressure aspiration pump for ventilation
What are the two major clades within living Amniota
Synapsida: All mammals
Diapsida: Includes Archosauria (birds, crocodiles), turtles, and Lepidosauria (including Squamata)
What are the four extra-embryonic membranes in the amniotic egg and their functions
Amnion: Cushions embryo in amniotic cavity
Allantois: Stores nitrogenous waste and aids gas exchange
Chorion: Involved in gas exchange with the allantois
Yolk sac: Provides nutrients (also present in non-amniotes)
Why is the allantois considered a key evolutionary innovation
It provides a large surface area for gas exchange and waste storage, allowing larger eggs and adaptation to dry environments
What is the process of shell formation in amniotes
The mother’s oviduct secretes albumen, lays down shell membranes, and then (if applicable) a calcareous shell around them
What is the earliest fossil evidence for the amniotic egg
Indirect evidence of live-bearing in the Permian marine reptile Mesosaur
How is live-bearing supported physiologically in amniotes
Via extra-embryonic membranes forming a chorio-allantoic placenta, especially in mammals
What groups are included in Squamata
Snakes, “lizards,” and amphisbaenians
What are some recurring evolutionary trends in squamates
Limb reduction or loss
Evolution of live-bearing
Evolution of gliding/wings in some lizards
What extinct group of marine squamates dominated the seas in the Late Cretaceous
Mosasaurs – large, predatory marine reptiles and sister group to snakes
What’s the difference between endotherms and ectotherms
Endotherms: Maintain constant body temperature via high metabolic rates (e.g. mammals, birds)
Ectotherms: Body temperature depends on environment; low resting metabolic rate (e.g. all living squamates)
What is an example of facultative endothermy in a living squamate
Female pythons generate heat by shivering to brood eggs
What evidence suggests mosasaurs were endotherms
Bone isotope data indicating high internal body temperatures (Harrell et al. 2016)
How do ectotherms thermoregulate behaviourally
By modifying environmental energy flows (e.g. basking, burrow use, time of activity)
What’s an example of extreme behavioural thermoregulation
Liolaemus signifer lizard emerges at -5˚C to bask on insulating vegetation
Why are ectotherms more shape/size flexible than endotherms
Lower mass-specific metabolic rate allows smaller body sizes and adaptation to low-energy environments
Why is biomass conversion more efficient in ectotherms
Lower metabolic demands allow them to convert food energy more efficiently.
How do squamates thrive in low productivity environments
They require less food and feed less frequently due to low energy requirements and efficient biomass conversion
What are the ancestral feeding behaviours in snakes
Constriction and ambush predation
How does venom delivery strategy differ between elapids and pit vipers
Elapids: Strike and hold
Pit vipers: Strike and release, then track prey chemically via venom proteins
What sensory system allows snakes to track envenomated prey
Vomeronasal organ and forked tongue – for olfactory chemosensation
What are pit organs and which snakes have them
Infrared heat-sensing organs; found in pit vipers, boids, and pythons
What is special about the tentacled snake
Uses mechanosensory tentacles to detect water movement; uses deceptive movement to direct fish into its jaws
