EEB384H1 Lecture Notes - Lecture 3: Shoulder Girdle, Casineria, Skull
22 Feb 2017
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All extant reptiles fall within clade called amniota. Reptiles and amphibians radiated at around same time. Contains a lot of taxa that are pretty obscure: a lot of obscure fossil groups. Earliest fossil we can consider an amniote is casineria: found in paleozoic, found about 340 million years ago, notable feature: Makes it a bit uncertain about where this fossil might be classified. Casineria has a five-digit foot: = prototype amniote digit pattern, many early amphibians have more than 5 digits. Also has claws: no claws in most amphibians. Some traits key to identifying amniotes: have eggs with amniotic membranes and fibrous shells. Proposed that the first step of evolution of amniotic egg was evolution of fibrous shell: = protection from membrane, structurally stronger. Calcareous shells can be sat on: can also build a bigger eggs. Will have harder time getting oxygen into egg (smaller sa:v ratio)
