Reptilian Ancestors of the Lizards, Snakes & Crocodiles

Reptiles come from the scientific class "Reptilia" which houses nearly 6,000 species of cold-blooded vertebrate reptiles. In our modern world, the reptiles we see today are split into four groups: crocodilians (alligators and crocodiles), turtles, tuataras and lizards/snakes. All together this genetic line spans roughly 300 million years back in time to a set of original ancestors that filled the niche of our modern day reptiles.

  1. Labyrinthodontia

    • The ancestor that was the predecessor for today's modern amphibians (class Amphibia), Labyrinthodontia is the earliest large amphibian group directly linked to evolution of reptiles, making modern day reptile amphibians --- crocodiles, turtles, aquatic snakes --- living and breathing descendants of Labyrinthodonts. Labyrinthodonts were found exclusively during the Triassic and Palaeozoic periods, making them one of the older reptilian ancestors.

    Cotylosaurs

    • As reptiles gradually exited the water for longer spans of time until their lives no longer centered around it, a distinct group known as cotylosaurias separated itself from amphibians. Cotylosaurs were physically similar to modern lizards and had teeth closely resembling their labyrinthine aquatic cousins. Cotylosaurs are regarded as the most basic and ancient ancestors for all land-living reptiles such as tortoises, land snakes and lizards.

    Synapsida, Anapsida and Disapsida

    • Branching from land-living cotylosaurs, synapsida fossils show links to them as the ancestors to "mammal-like reptiles" such as pelycosaurs and dimetrodons. Anapsids branched off to form various land-living varieties such as pareiasaurs, millerettids and procolophonoids (modern day tortoises). All other modern land-living reptiles, such as snakes and lizards, come from the group diapsida.

    Modern Classification

    • After the millions upon millions of reptilian generations, four modern categories have emerged. Emerged from the archosaur group Pseudosuchia, modern day crocodilians --- alligators, crocodiles and camiens --- belong to the reptile order Crocodilia. Descendants of Anapsida, turtles and tortieses are members of the order Chelonia. Tuataras are classified to the order Sphenodonta and lizards/snakes are members of the modern order Squamata, making both tuataras and lizards/snakes descendants of lepidosaurs.