A NEW MIOCENE GERRHONOTINE FROM THE CALIENTE FORMATION, CALIFORNIA

Gerrhonotinae (i.e. alligator lizards) is an extant lizard clade with a rich Cenozoic fossil record in the Americas and a diverse assemblage of species still inhabiting regi­­ons of North and Central America. There are 55 extant species in six genera, but because many extant species are rare in museum collections there is currently a lack of published skeletal data, hindering accurate identification of fossils. Here, I describe a new gerrhonotine lizard known from a partially complete articulated skull from the University of California Museum of Paleontology (UCMP). Only two gerrhonotine skulls have been previously described. The UCMP specimen is from the Caliente formation in southern California and is 11.5-12.5 Ma old (Miocene, Clarendonian North American land mammal age). I used x-ray computed tomography (CT) scans to visualize the specimen and elucidate cranial anatomy that is inaccessible from the physical specimen alone. The new taxon is unique among gerrhonotines in that it possesses cephalic osteoderms with tall, sail-like keels, which is a trait previously unobserved in gerrhonotines. To place the fossil phylogenetically and taxonomically, I conducted phylogenetic analyses of Gerrhonotinae using both molecular and morphological data. These analyses incorporate morphological characters that are new to the literature as well as novel osteological CT data for many species. Preliminary analysis indicates that the specimen represents a new species and a potentially new genus of gerrhonotine. Additionally, I describe two other lizard fossils found in the same assemblage to help provide a paleoecological interpretation of the gerrhonotine fossil.