Effects of phylogenetic uncertainty on fossil identification illustrated by a new and enigmatic Eocene iguanian Project ID: 0000C1066 Public

1 Media · 1 Specimen · Managed by: Simon Scarpetta

Pleurodonta (Squamata: Iguania) is an ancient and frequently-studied lizard clade for which phylogenetic resolution is elusive. Systematic diagnoses of fossil pleurodontans are confounded by that topological uncertainty and vary among approaches used for fossil identification. Here, I describe a new pleurodontan from the Eocene deposits of the Willwood Formation, Wyoming. To elucidate the systematic position of the fossil, I performed extensive phylogenetic analyses with several molecular scaffolds, two matrices, and Bayesian and parsimony methods. The relationships of the new taxon are largely contingent on topological hypothesis. Future efforts to identify fossil pleurodontans lacking unambiguous apomorphies of specific clades should consider alternative topological hypotheses, especially those derived from molecular data. That suggestion is generalizable to any clade lacking a consensus phylogeny. Biogeographic and paleoecological hypotheses based on the new taxon are contingent on its systematic placement, and so detailed interpretations await further refinement of it relationships. I urge similar caution for other fossils of uncertain systematic affinity.