A PECULIAR ICHTHYODETIFORM FISH FROM THE UPPER CRETACEOUS WOODBINE FORMATION OF DENTON COUNTY, TEXAS, USA

DMNH 20149 is a 96 million-year-old, nearly complete skeleton of an actinopterygian bony fish housed in the Perot Museum of Nature and Science in Dallas, Texas, USA. It was collected in Denton County, Texas, from the Upper Cretaceous Woodbine Formation (mid-Cenomanian) within the Arlington Member representing a deltaic deposit formed along the Western Interior Seaway of North America. DMNH 20149 presently exposes the right lateral side and measures about 39 cm and 50 cm in standard length and total length, respectively. Based on preliminary observations, the body is laterally compressed and elongate (fusiform body plan) with the maximum body depth of about 11 cm. The overall skull morphology and body form of DMNH 20149 strongly suggest that it belongs to the order Ichthyodectiformes, a group of predatory, primitive teleosts that lived from the Middle Jurassic (Bathonian) to the Late Cretaceous (Maastrichtian). Ichthyodectiformes is known in the fossil record of every continent and is taxonomically diverse, consisting of three families, 22 genera, and 42 species. However, unlike previously described ichthyodectiforms, DMNH 20149 exhibits two notable features that make it distinct. The first feature is that DMNH 20149 is toothless. To date, all known Jurassic and Cretaceous ichthyodectiforms have teeth that range in size from minute teeth in Gillicus to large robust teeth in Xiphactinus. The second notable feature is that DMNH 20149 has a triangular dentary. Within Ichthyodectiformes, triangular dentaries are a characteristic found in Jurassic forms, whereas Cretaceous forms have a rectangular dentary. Therefore, these notable anatomical features suggest that DMNH 20149 is a new Late Cretaceous taxon that represents the last member of the ichthyodectiforms with the Jurassic jaw design.