A preliminary observation of a new skeletal specimen of a plethodid bony fish (Actinopterygii: Tselfatiiformes) from the Upper Cretaceous Eagle Ford Shale, Texas

A preliminary observation of a new skeletal specimen of a plethodid bony fish (Actinopterygii: Tselfatiiformes) from the Upper Cretaceous Eagle Ford Shale, Texas

Tselfatiiformes was a group of small to medium-sized actinopterygian fishes that lived during the Cretaceous. Recently, a new tselfatiiform specimen consisting of a nearly complete, articulated skull was discovered from the Upper Cretaceous Eagle Ford Shale in Texas. The specimen suggests that the fish was a deep-bodied form and possibly measured about 50 cm in total length. It exhibits pectoral fins high upon the flank, well-developed preopercles, large infraorbital bones, and well-developed branchiostegal rays. These anatomical characteristics suggest its phylogenetic affinity within the tselfatiiform family Plethodidae. The morphology of the paired premaxillae, which are fused together and massive but do not form a ‘snout’, is reminiscent of that of the poorly known genus Plethodus although further examination is necessary to determine its exact taxonomic identity. Whereas it is possible that the specimen may belong to a new taxon, it is considered important even if it belongs to Plethodus, because the genus is currently known only from primarily disarticulated incomplete remains. Furthermore, it is also phylogenetically significant because it is anticipated to shed light on the evolution of the ‘snouted’ tselfatiiforms, such as Thryptodus and Martinichthys characterized by an elongated rostrum composed of fused premaxillae.