A new pachyrhizodontid fish (Actinopterygii: Teleostei) from the Tarrant Formation (Cenomanian) of the Upper Cretaceous Eagle Ford Group of Texas, U.S.A.
Date of Award
Master of Science (MS)
Jason Bystriansky, PhD
Windsor Aguirre, PhD
Kenshu Shimada, PhD
SMU 76938 is a fossil skeleton of a large, nearly complete actinopterygian bony fish housed in Southern Methodist University in Dallas, Texas, USA. It was collected from the Upper Cretaceous Tarrant Formation (middle Cenomanian; ~96 Ma) of the Eagle Ford Group in Tarrant County, Texas, an area where it was near the western margin of the East Texas Embayment during the Late Cretaceous. Although parts of the skull and dorsal fin are damaged, SMU 76938 is relatively complete, especially in the preservation of the caudal fin with its soft tissue outline. The fish has a fusiform body and measures about 93, 109, and 119 cm in standard length, fork length, and total length, respectively, and about 17 cm in maximum body depth. Several features of SMU 76938 are reminiscent of Cretaceous crossognathiforms, yet many features, such as the villiform dentition, have yet to be seen in any taxa within the order. My phylogenetic analysis indicates that SMU 76938 is a pachyrhizodontid crossognathiform fish. The combination of villiform teeth and fused infraorbital 1 and 2 in SMU 76938 is unique, suggesting that the specimen belongs to a new genus and species within the family Pachyrhizodontidae. With a fusiform body, a large symmetrical caudal fin, and a mouth with numerous small conical teeth suited for grasping, the new taxon represented by SMU 76938 was most likely a fast swimming, open-ocean predator capable of high propulsion and quick bursts of speed, that likely pursued smaller, quick swimming animals, such as squid, crustaceans, and other fishes. Although the individual represented by SMU 76938 was about 14 years old at the time of its death, my 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.
London, Maxwell G., "A new pachyrhizodontid fish (Actinopterygii: Teleostei) from the Tarrant Formation (Cenomanian) of the Upper Cretaceous Eagle Ford Group of Texas, U.S.A." (2019). College of Science and Health Theses and Dissertations. 336.