A green river (Eocene) polychrotid (Squamata : Reptilia) and a re-examination of iguanian systematics

摘要

A pleurodontan iguanian from the Green River Formation (Eocene) is described in detail and named. The new taxon is known only from a single specimen preserving all areas of the body. Although many of the bone surfaces are eroded, almost all of the skeleton is present and some cartilaginous elements are preserved. The new taxon shares important characteristics with the extant anisolepines and leiosaurines, including the morphology and placement of the caudal autotomy planes, the postxiphisternal inscriptional ribs, and notched or fenestrated clavicles that are expanded proximally. This is the earliest complete iguanian known from the Americas and the earliest known iguanian that may be confidently referred to an extant "family." A phylogenetic analysis including this taxon and other fossil and extant iguanians offers some support for the monophyly of Polychrotidae sensu lato, Tropiduridae sensu lato, and non-acrodont iguanians (Pleurodonta).