Evolution and systematics

Originally the family Xenosauridae included two genera, Xenosaurus from Mexico and Central America and Shinisaurus from China. However, in 1999, J. Robert Macey and colleagues removed Shinisaurus from Xenosauridae and placed it into its own family (Shinisauridae) on the basis of DNA evidence. This same study places Xenosauridae in close relationships with the families Shinisauridae, Anniellidae, and Anguidae.

As of 2002, there were six described species of xenosaurs, including one described in 2000 (X. penai) and one in 2001 (X. phalaroantheron). Given the isolation of many Xenosaurus populations and their low mobility, it will not be surprising if further research finds several more undescribed species of Xenosaurus. No subfamilies are recognized.

There is no fossil record for the extant genus Xenosaurus. Fossils of three extinct xenosaurid genera have been found in North America and Europe.

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