SMALL DIAPSID SKELETONS FROM THE LOCKATONG FORMATION (UPPER TRIASSIC) OF THE EASTERN UNITED STATES AND THE SYSTEMATICS OF EARLY SAURIAN REPTILES

The early radiation of Sauria (the group containing archosaurs and lepidosaurs) remains poorly understood, despite its importance in understanding the biotic recovery following the Permo-Triassic Extinction and the evolution of small reptiles during the Triassic. Poor phylogenetic resolution among early saurian lineages is driven by a meager diapsid fossil record in the Permian and earliest Triassic, and a generally poor record of small reptiles for the Triassic Period. Indeed, when preserved, small diapsids tend to be represented by badly crushed skeletons, or three-dimensionally preserved but isolated elements, both of which are problematic for phylogenetic analysis.

The Upper Triassic Lockatong Formation (Newark Supergroup) has produced remarkable skeletons of small diapsids, including Tanytrachelos ahynis, Hypuronector limnaios, and Icarosaurus siefkeri. These specimens are remarkable for the partial three-dimensional preservation of certain elements, and thus provide a strong framework for the interpretation of both heavily crushed skeletons and isolated, three-dimensionally preserved elements. The association of specimens with such different states of preservation is essential for phylogenetic studies. Despite these qualities, the Lockatong materials have rarely been incorporated into analyses.

I re-examined these Lockatong reptiles and integrated them into a phylogenetic analysis concentrating on early saurians. Tanytrachelos ahynis is recovered as a derived tanystropheid. With comparisons with the Lockatong Tanytrachelos materials, I was able to identify many isolated tanystropheid elements from western North America. Hypuronector limnaios is recovered as the basalmost drepanosaur, a position that supports the hypothesis that drepanosaurs are not saurians. The kuehneosaurid Icarosaurus siefkeri likewise supports the association of isolated materials from European fissure fills, but the association of Kuehneosauridae with Lepidosauromorpha is questionable. Continued sampling of the Lockatong Formation thus has the potential to provide specimens critical to understanding Triassic reptile phylogeny.