amniotes Flashcards
What is thought to be the first amniote
Westlothiana
-Aminotes = prescence of amniotic egg
what is the amniotic egg
The amniotic egg of reptiles and birds is surrounded by a tough outer shell that protects the egg from predators, pathogens , damage, and drying.
What make sup the amniotic egg
1) extraembryonic membranes:
- chorion, = surrounds everything
- allantois, = where nitrogenous waste gets deposited (becomes bladder)
- amnion = surrounds the embryo
2) yolk sac (food source)
3) all of egg surrounded by albumen (egg white)
- in some species surrounded by a hard shell
Why do birds lay eggs with hard shells
allowed them to lay eggs in dry environments on land
the name for mammals that lay eggs
monotremes
examples of non-egg laying amniotes
- placentals
- marsupials
How do no-egg amniotes differ from amniotic egg laying organisms
1) Embryo layers are homologous (essentially same structure except attached to placenta )
2) Allantois is vascularised for gaseous exchange, ^ SA for gas exchange
- Larger eggs = larger offspring, theory for why amniotes evolved , larger eggs on land.
What are some derived features of amniotes
1) skin permeability, thicker keratinised, more lipids -> scales, hair and feathers are all homologous structures
2) coastal ventialltion - allows longer necks
3) more complex nerves controlling forelimb (allows increased movement)
What are the 4 types of temporal fenestration
1) Anapsid (no arches) - 1 hole
2) synapsid ( one arch) - 2holes
3) Diapsid (2 arches) - 3 holes
4) Modified diapsid, lower temporal lost, 2 holes
what are the two main groups of diapsids
1) lepidosaurs - Tuatara, snakes + lizards
2) archosaurs - crocodiles, dinosaurs + birds
what type of skull do mammals have
highly modified synapsid skulls
What is the function of the holes in the skull
- allowed the expansion of muscles e.g. larger jaws
- muscles go through skull and attach to the top
- thought to have evolved during development of skull, muscles went through before skull could join, kept happening more regularly forming permanent holes in skull
Turtle (chelonia) features
1) fossile from 220 mya
2) no teeth, lost over course of evolution
3) Shell is restricitive but provides great defence
4) shell is made of carapace (top) and plaston (underneath)
5) can bend neck into shell
Environmental sex determination in turtles
- in turtles females are produced at higher temperatures
- ususally the bigger sex is produced at higher temperatures, e.g. lizard are opposite to turtles
E.g. Kemp’s Ridley turtles - breed in specific place in mexico, another population was set up for breeding however it was not getting enough females, thus they realised the link between temp and sex in turtles
Features of squamates (lizards + snakes)
1) 95% of all extant reptile s
2) Mostly diapsid skull, some have modifications such as snakes for more flexible heads
3) vary a lot in size
4) Most larger forms are herbivorous
5) limb reduction evolved many times (>60), associated with burrowing or living in vegetation
