A new classification of a Pliocene fossil lizard (Anguidae: Gerrhonotinae) from Anza-Borrego Desert State Park, California

The lizard group Gerrhonotinae, commonly known as alligator lizards, includes over 50 extant species distributed across the western and central United States, Mexico, and Central America. For many of these species, skeletal data are limited or non-existent. The lack of material is a major obstacle for understanding the cranial osteology of this group. I address the lack of traditional skeletal material with the use of X-ray computed tomography data (CT). CT imaging allows me to analyze the cranial osteology of these lizards in detail while also providing new skeletal data for a number of gerrhonotine species. Known gerrhonotine fossils are almost exclusively cranial elements, and thus an understanding of extant species cranial osteology has important implications for a knowledge of interspecific and intraspecific variation. I use my newly obtained CT images of skeletal data to assess the phylogenetic relationships of a fossil gerrhonotine skull (LACM 10601) from the Pliocene. This well-preserved fossil skull is from the Palm Spring Formation in the Anza-Borrego Desert State Park in southern California. The fossil was preliminarily diagnosed as belonging to Gerrhonotinae. I hypothesize that it represents an unknown species of gerrhonotine lizard. By CT scanning this fossil skull, it is possible to elucidate evolutionarily derived features that provide evidence for the taxonomic placement of the fossil. The phylogenetic relationships, age, and location of the fossil allows me to comment on interesting paleobiogeographic implications.