Abstract

A new species of Eusthenodon from the Upper Devonian (Famennian) Catskill Formation was collected from associated talus blocks excavated during road construction along the northbound lanes of U.S. Route 15/Interstate 99 near Trout Run in Lycoming County, Pennsylvania, U.S.A. The new species is represented by isolated or partially articulated cranial bones, an anocleithrum, and body scales from several individuals. The new discovery is the second species of Eusthenodon described from the Catskill Formation after Eusthenodon bourdoni, a species found only at the Cogan House Exit Ramp locality, north of and up section from the Trout Run site. The new species is of a larger size category and exhibits qualities that distinguish it from E. bourdoni including a contact between posterior supraorbital and lacrimal bones that excludes the jugal from the orbital margin and scales with an ornamental field incised by radiating grooves. The clarity offered by the Catskill Formation Eusthenodon species informs an historical review of reports on Eusthenodon occurrence that suggests a polydemic but not cosmopolitan distribution of the taxon. A phylogenetic analysis of Tristichopteridae is presented that includes the new species presented here. The Eusthenodon species at Trout Run is the fifth tristichopterid species described from the Catskill Formation and all five are found to belong to a highly-nested clade of largely Famennian tristichopterids. With a growing fauna that additionally includes rhizodontids, dipnoans, holoptychiid porolepiforms, megalichthyids, and limbed tetrapodomorphs, the Catskill Formation of Pennsylvania continues to be an important focus for the study of Late Devonian sarcopterygian evolution.