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Sauria (Lacertilia; lizards; subclass Lepidosauria, order Squamata) A suborder of reptiles the more primitive of which are four-legged, terrestrial or arboreal forms, but limbless burrowing species have evolved in many families. The skin is generally shed in pieces. Autotomy is common. Lizards appeared and began to diversify in the Triassic. Their Jurassic history is poorly known, and except for remains of the sea-lizards, e.g. the mosasaurs, this is also true of much of the Cretaceous. However, from the late Cretaceous onwards continental deposits become more frequent again, and have yielded sufficient lizard fossils to trace the development of the group up to the present day. There are 18 extant families, found in all but the coldest parts of the world.