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What is an amniotic egg?
- 3 new membranes (amniote synapomorphy)
- 1. amnion: surrounds developing embryo and holds it in amniotic fluid. keeps embryo moist and protects it
- 2. chorion: outer membrane surrounds embryo and yolk, gas exchange with porous shell
- 3. allantois: repository for nitrogenous waste
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Other Derived characteristics of Amniotes
- Keratinized skin resistant to water loss
- hardened nails or claws
- lungs with greater internal surface area are filled by thoracic expansion (instead of buccal pumping)
- no larvae or metamorphosis
- loss of lateral line system
- further loss/reduction of skull elements
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When did amniotes originiate and what are the 3 major groups?
- Carboniferous (based on skull morphology)
- 1. anapsids
- 2. diapsids
- 3. synapsids
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Anapsida characteristics
- no temporal skull opening behind orbits (completely roofed by dermal skull bones)
- turtles tradtionally considered anapsids, but now considered derived diapsids based on new data
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Diapsida characteristics
- two temporal skull openings behind orbits (separated by bony arch)
- represented today by all living reptiles (traditionally minus turtles) & birds
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Diapsida: Lepidosauria
- all modern reptiles except crocodylians and turtles
- tuataras (most basal lineage) lizards, snakes, amphisbaenians
- >95% of living non-avian reptiles
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Diapsida: Archosauria
- corcodylians, birds & extinct groups (e.g. pterosaurs, dinosaurs)
- flight evolved twice in Archosauria (pterosaurs and birds)
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What kind of group are reptiles?
Paraphyletic, because birds are not included
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Turtles on the phylogenetic tree
- position under revision
- some data indicate relationship close to archosaurs (DNA)
- other data say closer to lepidosaurs (morphology)
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Synapsida characteristics
- one temporal skull opening behind orbits
- first linage to diverge from ancestral amniotes (basal to all other amniotes)
- gave rise to mammal lineage (only extant lineage)
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Characteristics of Class Reptilia
keratinized epidermal scales
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