A new pachyrhizodontid fish (Actinopterygii: Teleostei) from the Tarrant Formation (Cenomanian) of the Upper Cretaceous Eagle Ford Group in Texas, USA

Abstract

SMU 76938 is a nearly complete skeleton of a fossil bony fish, about 1.2 m in total length, housed in Southern Methodist University in Dallas, Texas, USA. It was collected from the Tarrant Formation (middle Cenomanian) of the Upper Cretaceous Eagle Ford Group in Tarrant County, Texas, an area where it was near the East Texas Embayment of the Western Interior Seaway during the Late Cretaceous. Our phylogenetic analysis indicates that it is a pachyrhizodontid crossognathiform fish, and comparisons with previously reported pachyrhizodontids suggest that the fossil fish belongs to a new genus and species within Pachyrhizodontidae, Polcynichthys lloydhilli gen. et sp. nov.. With a fusiform body, a large symmetrical caudal fin, and a mouth with numerous small conical teeth suited for grasping, the new taxon is interpreted to be a fast swimming, open-ocean predator that likely pursued smaller squid, crustaceans, and other fishes. Vertebral growth rings suggest that the individual was possibly about 14 years old at the time of its death, and our vertebra-based theoretical growth model indicates that the species could have reached up to about 1.8 m TL and lived up to 37 years old in age.