Question

Explain the evolution and the diversification of the early amniotes into contemporary reptiles. Use a phylogenetic tree to illustrate your answer.

Answer 1

The origin of reptiles is reported approximately around 300 million years ago ( during Carboniferous period). Casineria with characteristics of both amphibia and reptiles is one of the oldest known amniotes while Hylonomus is earliest one. After the emergence of the first amniotes they were divided into synapsids, anapsids and diapsids (during Permian period ). This period also witnessed a second major divergence of diapsid reptiles into archosaurs which are predecessors of crocodilians and dinosaurs and lepidosaurs which are the predecessors of snakes and lizards. These groups remained inconspicuous until the Triassic period when the archosaurs became the dominant terrestrial group due to the extinction of large-bodied anapsids and synapsids during the Permian-Triassic extinction. About 250 million years ago, archosaurs radiated into the dinosaurs and the pterosaurs.

Although they are sometimes mistakenly called dinosaurs, the pterosaurs were distinct from true dinosaurs. Pterosaurs had a number of adaptations that allowed for flight, including hollow bones (birds also exhibit hollow bones, a case of convergent evolution). Their wings were formed by membranes of skin that attached to the long, fourth finger of each arm and extended along the body to the legs.