The Origin and Early Diversification of Squamates

Abstract

Squamata, the group that comprises lizards, snakes, and amphisbaenians, is the largest and most diverse major group of living reptiles. Although most recent estimates place their divergence from Rhynchocephalia in the early Triassic, the first unequivocal records of squamates currently date from the Middle Jurassic, and the first crown squamates, representing Scincoidea, Anguimorpha, and possibly Gekkota, are known from the Late Jurassic. The record then improves substantially in the Early Cretaceous, with squamate fossils recorded from most major continents and showing evidence of expansion into a diversity of specialist niches. Despite recent claims to the contrary, the earliest unequivocal snake fossils also date from this period, with fragmentary remains from the Aptian-Cenomanian of North Africa and North America, followed by a more substantial global record from the Cenomanian onwards. The re-interpretation of the Middle Jurassic to Early Cretaceous parviraptorids as snakes was based on a misinterpretation of the original material, as shown by new associated specimens from the Middle Jurassic of Scotland.