Reptilia (Reptiles)

Abstract

Reptiles are a diverse group of vertebrates, including turtles, crocodiles, lizards and snakes, as well as the extinct dinosaurs, pterosaurs, plesiosaurs and ichthyosaurs. Reptiles lay cleidoic eggs (adapted to dry land), and they include the ancestors of birds and mammals. Key Concepts The ‘Reptilia’ is a paraphyletic group that includes turtles, lizards, snakes and crocodilians but excludes descendant birds and mammals. Reptiles include the majority of members of clade Amniota, the tetrapod group that lays eggs and are distinguished from amphibians by not having to lay eggs in water and by not having a larval stage for the young. The amniotic egg, with extraembryonic membranes and an allantois to collect waste, is shared by all modern reptiles, birds and mammals. Amniotes fall into two main clades based on their skull structure: diapsids with a double‐arched skull pattern and synapsids with a single, lower temporal opening; some amniotes either did not have temporal openings, or later lost them, the anapsid condition. Diapsid amniotes arose in the Carboniferous, and include modern lizards, snakes, crocodilians, birds, plus extinct dinosaurs and pterosaurs. Synapsid amniotes arose at the same time and include many extinct groups of so‐called mammal‐like reptiles, as well as mammals. There are over 11 050 species of living reptiles, mainly living in the tropics because of their ectothermic (externally regulated) thermophysiology.