Two genera comprise Xenosauridae, Xenosaurus and Shinisaurus. Xenosaurus (4 species) has a New World distribution and is found in rock crevices of mountainous regions of southeastern Mexico and Central America, while Shinisaurus (1 species) is Old World and found only in a small riparian area of southern China. That Xenosaurus and Shinisaurus are closely related has been questioned, and several herpetologists do not consider Xenosauridae to be a natural group, based on both morphological and molecular data.
Xenosaurids are generally rather small lizards, usually around foot or less long, whose bodies are covered with large, rough, projecting scales. They are usually rather darkly colored but may have colorful bands. Xenosauridae is united by the shape of the frontals, loss of the second epibranchials, and a widening of the postorbital branch of the jugal.
Xenosaurus eats primarily insects, although small vertebrates have been found in their stomachs. Shinisaurus eats tadpoles, frogs, and fish
Shinisaurus and Xenosaurus are both viviparous, bearing a few (< 5) or several (10-20) young, respectively. Xenosaurids are nocturnal or crepuscular, and saxicolous. Shinisaurus is semi-aquatic, basking on branches above water into which it drops into when disturbed.
Xenosaurids have no economic value to humans. Shinisaurus is CITES II listed (1990).
Xenosauridae belongs to the larger group Diploglossa (=Anguioidea), which also includes Anguidae (alligator lizards) and Anniellidae, although Diploglossa is probably not a natural group. Diploglossa belongs to Anguimorpha, a large group that includes the varanoids Helodermatidae (Gila monsters), Lanthanotidae (earless monitor), and Varanidae (monitor lizards).
Fossil xenosaurids include the Asian Carusia (late Cretaceous of Mongolia), and the North American Exostinus (Cretaceous and Oligocene), and Restes (Paleocene to Eocene).
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Jennifer C. Ast (author).