Reptiles In Focus

Welcome to the Reptiles section of In Focus. Reptiles are tetrapods with ectothermic metabolism and amniotic development, comprising four main orders: Testudines (turtles), Crocodilia (crocodilians), Squamata (lizards and snakes), and Rhynchocephalia (tuatara). There are over 12,000 living species currently recognized.

In traditional taxonomy, they belong to class Reptilia, but modern cladistic taxonomy views this group as paraphyletic since birds (class Aves) are closely related to crocodilians. Thus, some definitions of Reptilia include birds as part of a monophyletic group. The earliest proto-reptiles emerged in the Carboniferous period, evolving from advanced reptiliomorph tetrapods. The first true reptile, Hylonomus, appeared around 318 million years ago.

Extinct reptile groups, including non-avian dinosaurs and pterosaurs, largely disappeared during the Cretaceous–Paleogene extinction event. Modern reptiles are found on every continent except Antarctica. Most are oviparous, though some squamates are viviparous, with some species developing a placenta for their young. Reptile sizes vary greatly, from tiny geckos to the massive saltwater crocodile.