Geometric Morphometric Differentiation of Two Western USA Lizards (Phrynosomatidae: Squamata): Uta stansburiana and Urosaurus ornatus, with Implications for Fossil Identification

Abstract Squamate fossil identification has been challenging due to the incomplete understanding and sometimes complete lack of osteological research of extant species. Here we compared the maxilla of two similar species of phrynosomatids: Uta stansburiana (Common Side-blotched Lizard) and Urosaurus ornatus (Ornate Tree Lizard). Through landmark-based geometric morphometric analyses, we determined which characters significantly separated the two species. A principle component analysis (PCA) and a stepwise discriminant function analysis (DFA) were conducted, in which we compared 15 landmarks between U. stansburiana and U. ornatus. Both the PCA and stepwise DFA showed separation between the two species. The stepwise DFA selected five of the 15 characters as statistically significant, three of which are considered apomorphies and show promise for fossil identification. The first character is in the ventral region of the posterior maxilla process; U. ornatus has a defined notch, whereas U. stansburiana does not. The second and third characters are in the anterior portion of the maxilla, which is curved dorsally in U. stansburiana, whereas U. ornatus shows no curving. The results of this study are used to identify fossil Uta vs Urosaurus, but more analyses need to be conducted on other phrynosomatid species for comprehensive identification.