A redescription of Lophorhothon atopus (Ornithopoda: Dinosauria) from the Late Cretaceous of Alabama based on new material1

Abstract

Diagnostic dinosaur fossils of the southeastern United States are rare discoveries, and even more precious are those fossils that preserve a large portion of a skeleton. Sixty years ago, the dinosaur Lophorhothon atopus was described from Upper Cretaceous sediments of Alabama. It then represented the oldest, most complete, dinosaur in the southeastern United States. Based on a reexamination of the holotype material and a new specimen collected from the same beds, we provide a new diagnosis of this taxon. In particular, the solid nasal crest has several autapomorphies including caudally projecting frontal processes that are oval in cross section, meaning that they did not coalesce at the midline. Other autapomorphies are found on the prefrontal and squamosal. Combining the two Lophorhothon specimens provides nearly the entire skeleton for phylogenetic analysis, which we find as a hadrosauromorph just outside of Hadrosauridae. The original diagnosis of this taxon included the frontonasal fontanelle as a distinguishing character, but comparing the many examples of frontonasal openings across hadrosauromorph taxa shows that in at least a few species, such as Lophorhothon, the structures should be considered a frontonasal fenestra instead of a fontanelle. Additionally, the notion that dinosaurs from the East Coast of the United States represent primitive relicts is an idea that originated before many of the European and Asian hadrosauromorphs known today had been discovered. With new dating and phylogenetic information, it appears that Appalachian dinosaurs are on par evolutionarily with most of the global community and the term ”relict fauna” should be abandoned.