A Tyrannosauroid from the Lower Cenomanian of New Jersey and Its Evolutionary and Biogeographic Implications

Abstract

The Barremian through Turonian record of tyrannosauroids in North America is sparse, and neither the western nor eastern portions of the continent have produced substantial material of early tyrant dinosaurs. This is unfortunate, as the discovery and description of several new tyrannosauroid genera from this temporal interval in recent years has shown that this period of time was likely when the tyrannosauroids evolved many of the signature features of the large- bodied genera that famously roamed the planet during the latest Cretaceous. One particular trait of the younger tyrant dinosaur genera that seems to have evolved during the aforementioned temporal interval was that of large body size. Here, I describe the metatarsal II of an indeterminate tyrannosauroid from the Cenomanian Potomac Formation of New Jersey. The metatarsal II is significant for several reasons. It is the only definite occurrence of a tyrannosauroid in eastern North America (Appalachia) before the Coniacian and Santonian and indicates an animal in the size range of tyrannosauroids from the Santonian to Maastrichtian of the Cretaceous. The New Jersey specimen thus differs from other, mostly small and gracile, known tyrannosaur genera of the mid-Cretaceous, suggesting that the evolution of large size among tyrannosauroids was a complex process. The metatarsal has morphological affinities to the corresponding metatarsal II of Appalachiosaurus montgomeriensis, and along with the results of phylogenetic analysis this suggests that Late Cretaceous Appalachian tyrannosauroids were relict forms isolated on the landmass.