A tyrannosauroid tibia from the Navesink Formation of New Jersey and its biogeographic and evolutionary implications for North American tyrannosauroids

The sparse dinosaur record of eastern North America has rendered the dinosaurs of the Late Cretaceous landmass of Appalachia obscure. Appalachia may have been a refugium for dinosaur species that would be replaced on Appalachia's western contemporary, Laramidia, from which the former landmass was isolated by the Western Interior Seaway. Among the theropods of the landmass, Appalachian tyrannosaurs are only represented currently by the two valid taxa Dryptosaurus aquilunguis and Appalachiosaurus montgomeriensis, a distinct but indeterminate taxon from the Campanian of Delaware, and indeterminate skeletons and isolated elements. New Jersey in particular has rendered many bones assignable to tyrannosauroids, contributing much to the study of members of this clade from Appalachia. Here, the partial tibia of a tyrannosauroid is described from the Maastrichtian Navesink Formation of Monmouth County, New Jersey. The specimen, originally described by paleontologists Edward Drinker Cope and Joseph Leidy, is important for revealing further the theropod fauna of the Navesink Formation of New Jersey and being the second definite occurrence of a tyrannosauroid in eastern North America during the Maastrichtian, thus illuminating the group's ecology and biogeography during that stage of the Cretaceous. Phylogenetic analysis plots the Navesink specimen as the sister taxon to Bistahieversor in a larger polytomy of all tyrannosauroids more derived than Eotyrannus, suggesting that the Navesink bone may represent either another “intermediate”-grade tyrannosauroid from Appalachia or a relative of B. sealeyi that migrated to eastern North America after the regression of the Western Interior Seaway.