Evolution and systematics

Xantusiidae represents an ancient reptile lineage of uncertain relationships. The question what group of lizards constitutes the nearest relatives of Xantusiidae has long puzzled herpetologists. Night lizards resemble geckos in some features, but in other characteristics they appear more allied with teiids, lacertids, and skinks. Although the question continues to be debated by systematists, current evidence seems to indicate that xantusiids are probably most closely related to one of the latter three families, but which one remains a mystery. The fossil record extends back to the Paleocene, but it has shed little light on the origins of the family.

Also controversial is the question of relationships among the three living genera: Cricosaura (1 species), Lepidophyma (17 species), and Xantusia (5 species). Evidence from DNA sequences and from chromosomes indicates that the Cuban night lizard (Cricosaura typica) is the oldest separate lineage in the family, whereas characteristics based on internal and external morphology have been interpreted as evidence that Xantusia is the earliest branch. Subfamilies have been recognized within Xantusiidae but are not used in this account because of the small number of genera and the ambiguity of the evidence of relationships among them.

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