New material from the Upper Devonian (Frasnian) Fram Formation of Ellesmere Island, Nunavut, Canada, represents a new large-bodied species of Eusthenopteron. The complete and well-preserved nature of the fossil material enables a description of anatomy that is otherwise poorly represented in most Eusthenopteron species; this includes braincase (ethmosphenoid and otic-occipital), scapulocoracoid, and pectoral fin. The new species is distinguished from other Eusthenopteron species by its large body size, pitted rather than tuberculated dermal cranial ornament, a distinct caudolateral margin of the vomer, an unossified basicranium, and a horizontally oriented hyomandibula. A large sample size and decades of detailed study of Eusthenopteron foordi have resulted in an important anatomical understanding of that species, but a lack of autapomorphies has complicated efforts to diagnose the grouping Eusthenopteron. We review the taxonomic history of Eusthenopteron and provide a new diagnosis that relies on a combination of discrete features that are commonly preserved and unaffected by specimen quality.
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Vol. 562 • No. 1