Two characteristics that unite the squamates. The first is that they shed their skin periodically. Some squamates, such as snakes, shed their skin in one piece. Other squamates, such as many lizards, shed their skin in patches. In contrast, non-squamate reptiles regenerate their scales by other means—for example crocodiles shed a single scale at a time while turtles do not shed the scales that cover their carapace and instead add new layers from beneath.
The second characteristic shared by squamates is their uniquely jointed skulls and jaws, which are both strong and flexible. The extraordinary jaw mobility of squamates enables them to open their mouths very wide and in doing so, consume large prey. Additionally, the strength of their skull and jaws provides squamates with a powerful bite grip.
Squamates first appeared in the fossil record during the mid Jurassic and probably existed before that time. The fossil record for squamates is rather sparse. Modern squamates arose about 160 million years ago, during the late Jurassic. The earliest lizard fossils are between 185 and 165 million years old.
The closest living relatives of the squamates are the tuataras, followed by the crocodiles and birds. Of all living reptiles, turtles are the most distant relatives of the squamates. Like crocodilians, squamates are diapsids, a group of reptiles that possess two holes (or temporal fenestra) on each side of their skull.