A new genus and species of large macrodont actinopterygian from the Pennsylvanian (Kasimovian/Missourian) atrasado formation of New Mexico

The skull of a large, three-dimensionally preserved actinopterygian from the Late Pennsylvanian (Kasimovian) Tinajas Member of the Atrasado Formation near Socorro, New Mexico is described as a new genus and species with the aid of micro-computed tomography. Scans reveal substantial details of internal cranial anatomy, including the braincase, palate, and gill skeleton. Noteworthy features that differentiate this taxon from generalized Palaeozoic actinopterygians include: multiple ossifications of both the braincase and palatoquadrate; partial re-enclosure of the lateral dorsal aortae following their exit from the basicranium; a lacrimal that contributes to the gape and bears teeth; large, well-spaced fangs on both the dentary and mandible; horizontally directed teeth on the entopterygoid and dermopalatines; broadly separated cotyles of the articular. Some aspects of anatomy, such as large fangs on the anterior coronoid and a moderately elevated articular region of the lower jaw, may be of taxonomic utility. The new taxon shows close correspondence to the Mississippian (Viséan) Watsonichthys pectinatus from Scotland, but differs from it in the shape of the anterior parasphenoid process and the presence of a toothed lacrimal. The relationships among fanged late Paleozoic actinopterygians are highly uncertain, in large part due to the limited morphological data available for many members of this assemblage of fishes. We make comparisons with other large, fang-bearing actinopterygians of Carboniferous–Permian age, and propose a set of research priorities aimed at addressing this “macrodont problem.” https://zoobank.org/urn:lsid:zoobank.org:pub:49A6BD22-6CFC-4C97-8B2F-AEF9D571D90B