PALEOBIOGEOGRAPHICAL IMPLICATIONS OF A NEW ORNITHOMIMOSAUR DINOSAUR FROM THE EARLY CRETACEOUS TRINITY GROUP OF ARKANSAS

Ornithomimosaurs (ostrich-mimic dinosaurs) are well known from Asia during in the Early Cretaceous, but they are less well known from this time in North America. Represented by a single specimen consisting of pedal elements, a new North American taxon, which consists of a nearly complete right foot, recovered from the Lower Cretaceous (Albian/Aptian) Trinity Group of Arkansas. The Arkansas ornithomimosaur can be distinguished from other ornithomimosaurs based on a laterally compressed third metatarsal, while also possessing a unique combination of synapomorphies. The condition of this third metatarsal suggests that the Arkansas ornithomimosaur is more basal than other Asiatic ornithomimosaurs of similar age, but consistent with older North American forms, such as the oldest known North American ornithomimosaur, Nedcolbertia. The Arkansas specimen and Nedcolbertia are more basal than other Asiatic ornithomimosaurs of similar age, and correlate more strongly with the European Wealden fauna, indicating that an early dispersal event from Laurasia took place sometime before or during the Barremian. During the Aptian, species would have been able to move east-west across southern North America, which was not yet bisected into the ancestral Laramidia and Appalachia by the influx of the Skull Creek Seaway. This paleogeographic situation allows for the co-mingling of species across southern North America during the Early Cretaceous, and could have allowed for the ornithomimosaur Nedcolbertia to dispersed back to ancestral Appalachia, where later forms evolved into the Arkansas specimen, or an existing Appalachian ornithomimosaur, more distantly related to Nedcolbertia, evolved into the Arkansas specimen.