A new species of Eusthenodon (Sarcopterygii, Tristichopteridae) from the Upper Devonian (Famennian) of Pennsylvania, U.S.A., and a review of Eusthenodon taxonomy

Abstract

ABSTRACT A new species of Eusthenodon from the Upper Devonian (Famennian) Catskill Formation was collected from talus blocks at the base of a road cut along the Cogan House Exit Ramp on U.S. 15/Interstate 99 in Lycoming County, Pennsylvania, U.S.A. The new species is represented by a nearly complete, articulated skull (ANSP 23748) and additional cranial bones, body scales, and pectoral girdle elements. The breadth of anatomy represented by the new fossils, and the quality of their preservation and preparation, enable a detailed anatomical description of a new species. The original diagnosis of Eusthenodon distinguished the taxon from Tristichopterus and Eusthenopteron, the only other described tristichopterids at the time. The descriptive qualities of the Eusthenodon wangsjoi type material do not diagnose Eusthenodon from among the highly nested tristichopterid taxa that have been discovered since the original publication. In an effort to strengthen the taxonomic status and phylogenetic utility of Eusthenodon, we propose a revised diagnosis that uses only discrete, commonly preserved features that are unlikely to be altered by deformation. The new species is the third described Catskill Formation tristichopterid along with Hyneria lindae and Langlieria radiatus. All three are large-bodied and in a highly nested phylogenetic position within the group. The presence of a single tristichopterid species at each site highlights temporal and spatial regionalization of the Catskill fauna and may, along with a suite of anatomical features, support the hypothesis that tristichopterids occupied the role of top predator in the freshwater ecosystems of the Catskill Delta complex.