Who Are the Ancestors of Reptiles?

Labyrinthodontia

• All reptiles originally emerged out of today's animal group, the amphibians (class Amphibia). One of the earliest forms of amphibians connected to the evolution of reptiles are members of the group Labyrinthodontia. Labyrinthodonts existed during the Triassic and Palaeozoic periods.

Cotylosaurs

• Reptiles eventually became a distinct animal group from amphibians, with one of the most primitive reptile orders being Cotylosauria. Cotylosaurs were lizard-like animals that had still had teeth extremely similar to labyrinthine amphibians. Also called stem or root reptiles, cotylosaurs included varieties such as members of the group Pareiasauridae. Pareiasauridae reptiles were herbivores that grew up to 10 feet in length.

Synapsida, Anapsida and Diapida

• The next major evolutionary wave came with of the emergence of the reptile divisions Synapsida, Anapsida and Disapsida. Synapsids were originally considered "mammal-like reptiles", and included various animals such as pelycosaurs and dimetrodons. However, as of the time of publication, most experts believe that members of Synapsida were not actually reptiles. Anapsids included varieties such as pareiasaurs, millerettids, procolophonoids and turtles. Diapsida is the group that most reptiles gradually emerged from. One of the earliest diapsids is the lizard-like, Petrolacosaurus.

Lepidosauria and Archosauria

• Over time, Diapsida split into other reptilian divisions. The group Lepidosauria consisted of scaly reptiles that became today's lizards, snakes and tutura. Archosauria is the group that encompassed dinosaurs, pterosaurs and what are today's crocodiles and alligators.

Lepidosaurs

• Ancient lepidosaurs included members of several groups including Eosuchia, Claudiosaurus and Coelurosauravids, all of which lived during the Permian and Triassic eras.

Archosaurs

• The archosaurs thrived during the Permian, Triassic and Jurassic periods, and included members of the groups Ornithosuchia and Pseudosuchia. Ornithosuchia consisted of pterosaurs and dinosaurs, while Pseudosuchia included aetosaurs, phytosaurs and crocodiles.

Modern Classifications

• After millions of years of reptile generations, only four living orders of Reptilia remain. The alligators and crocodiles belong to the reptile order Crocodilia, which emerged from the archosaur group Pseudosuchia. Turtles are members of the order Chelonia, and are the only living reptile group from Anapsida. Tuataras belong to the order Sphenodonta; whereas lizards and snakes are members of the order Squamata. Both Sphenodonta and Squamata emerged from lepidosaurs.