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

Second species ofEusthenodon(Tristichopteridae, Sarcopterygii) from the Upper Devonian (Famennian) Catskill Formation of Pennsylvania, U.S.A., and a review of globalEusthenodonoccurrence

“…The parietal shield dimensions of ANSP 21342 (width/length ratio of parietal shield = 0.51, with width measured as maximum width across the parietals; Fig. 7B) suggest that E. leganihanne had a relatively wide skull with a blunt snout, similar in shape to those of E. bourdoni (0.55 in ANSP 23748; Downs et al, 2021) and E . wangsjoi (∼0.51 in NHMD 141691 [=P.1478of Jarvik, 1952), and dissimilar then to both the "narrow and acutely pointed head" that contributes to the diagnosis of M. fairfaxi (∼0.38 in F96508; Johanson & Ahlberg, 1997, p. 46).…”

“…These authors proposed a new diagnostic combination for Eusthenodon that included three cranial features that are all discrete, commonly preserved, and not susceptible to deformational change. It is with consideration of this diagnosis, and the species diagnosis for E. bourdoni (Downs et al, 2021), that we assign the new tristichopterid fossils from the Trout Run locality to a new species, the third recognized for Eusthenodon. The work we present here offers a description of the Eusthenodon fossils from the Trout Run locality, an historical review of reports on Eusthenodon occurrences, and a new phylogenetic analysis of Tristichopteridae that includes the new species from the Trout Run locality.…”

“…Type Species-Eusthenodon wangsjoi Jarvik 1952 Diagnosis-Tristichopterid distinguished by the following combination of characters: a denticulated field of the parasphenoid that is recessed into the body of the bone, a squamosal that overlaps the maxilla, and a marginal tooth row of the dentary that does not reach the symphysis (Downs et al, 2021).…”

“…Among the 26 original diagnostic qualities of Eusthenodon, 18 are non-discrete and arbitrarily defined (as in "orbital fenestra … less than 0.3 of the length of the parietal shield, " Jarvik, 1952:p. 54) or rely on one's interpretation of the author's qualitative language (as in "parietal shield short and broad, " Jarvik, 1952:p. 54). The remaining eight discrete features do not distinguish Eusthenodon from among the many other highly nested tristichopterid taxa that have been described in the years subsequent to Jarvik's (1952) publication: Hyneria lindae Thomson 1968, Mandageria fairfaxi , Cabonnichthys burnsi Ahlberg & Johanson 1997, Langlieria socqueti Clément et al 2009, Edenopteron keithcrooki Young et al 2013, Langlieria radiatus (Newberry, 1889, Eusthenodon bourdoni Downs et al 2021, and Langlieria smalingi Downs & Daeschler 2022. Downs et al (2021 performed a character by character assessment of Jarvik's (1952) diagnosis and compiled a complete historical review of the Eusthenodon taxonomic work that followed in the subsequent decades.…”

“…The material includes partially articulated cranial remains, isolated cranial bones, an anocleithrum, and numerous body scales. Downs et al (2021) described E. bourdoni from remains collected at the Cogan House Exit Ramp locality along the southbound lanes of U.S. Route 15/Interstate 99 in Lycoming County, Pennsylvania. In that work, the authors alluded to the current subject when they wrote of an "undescribed, largebodied tristichopterid […] near Trout Run in Lycoming County" (Downs et al, 2021).…”