Evolution and systematics

The Anguidae is a monophyletic group within the An-guimorpha and is related most closely to either the Vara-noidea (Varanidae, Lanthanotidae, and Helodermatidae) or the Xenosauridae and Shinisauridae. The 14 anguid genera are classified among four subfamilies as follows: Anguinae (glass lizards and slowworm—Ophisaurus and Anguis), An-niellinae (legless lizards—Anniella), Diploglossinae (galliwasps and allies—Celestus, Diploglossus, Ophiodes, Sauresia, and Wetmorena), and Gerrhonotinae (alligator lizards—Abronia, Barisia, Coloptychon, Elgaria, Gerrhonotus, and Mesaspis).

Phylogenetic analyses of DNA sequence data strongly support the monophyly of the Anguidae and three of its subfamilies, but monophyly of the Diploglossinae requires further evaluation. These analyses also suggest that the Gerrhonotinae and Anguinae are sister taxa and that the Anniel-linae is the most basal subfamily. Within the Anguinae, Ophisaurus is paraphyletic with respect to Anguis; the geographically proximate A. fragilis and O. apodus are sister taxa. Within the Diploglossinae, Sauresia and Wetmorena appear to be sister taxa, and Ophiodes is related closely to the West Indian Diploglossus. Studies with a denser sampling of diploglos-sine taxa are needed to evaluate these findings further. Within the Gerrhonotinae, available data support a sister relationship between Elgaria and the other genera.

Fossils from the late Cretaceous (ca. 75-95 million years ago) of Europe have been assigned to a distinct subfamily (Glyptosaurinae) within the Anguidae. European fossils that may represent anguines or their close relatives are known from the Middle Eocene and later, and, according to J. A. Gauthier, fossils assigned to the Anguis-Ophisaurus apodus clade date back to the late Oligocene or early Miocene. On the other hand, Ophisaurus fossils are not known from North America before the late Miocene. The fossil record indicates that each anguid subfamily originated at least by the early Eocene (50-55 million years ago).

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