Dryptosaurus

Abstract: ABSTRACT Although among the first theropod dinosaurs known to science, and an iconic taxon in the history of dinosaur paleontology, the large carnivore Dryptosaurus aquilunguis from the Late Cretaceous of New Jersey remains poorly understood. Its anatomy has been described only in brief and its phylogenetic relationships have long been the subject of debate, although recent work proposes Dryptosaurus as a member of the tyrannosauroid clade. Here we present a thorough osteological description of the holotype of Dryptosaurus aquilunguis, supplemented with photographs of all the material, and provide extensive comparisons with other theropods, especially tyrannosauroids. In concert with recent phylogenetic analyses, our description confirms the tyrannosauroid affinities of Dryptosaurus and supports its placement as an “intermediate” taxon bracketed between small, basal forms (e.g., Guanlong, Dilong) and the derived, Late Cretaceous tyrannosaurids (e.g., Albertosaurus, Tyrannosaurus). We identify several autapomorphies of Dryptosaurus, including the combination of a reduced humerus and an enlarged hand. These forelimb proportions, which differ from the uniformly large arms of basal tyrannosauroids and uniformly atrophied arms of tyrannosaurids, suggest that forelimb reduction in tyrannosauroids may not have proceeded in a uniform fashion. Functionally, Dryptosaurus may have used both its skull and arms as weapons for prey acquisition and processing.

Abstract: The skeleton of the enigmatic theropod Dryptosaurus aquilunguis is redescribed in light of the many new theropods named since Cope's original description in 1866 Unfortunately, the fragmentary nature of the single known skeleton makes comparison with other theropods difficult Historically, Dryptosaurus has been placed, at one time or another, in the theropod families Coeluridae, Deinodontidae, Megalosauridae, Tyrannosauridae, and its own family, Dryptosauridae Most of these assignments have been based upon superficial resemblances to various members of those families Reexamination of the specimen indicates the presence of unique serrations on the maxillary teeth, a large ungual/humeral ratio, the probable presence of a high, centrally located ascending process on the astragalus, and a non-arctometatarsal These features indicate that Dryptosaurus is a unique theropod and should be placed in its own family, Dryptosauridae

Abstract: During the Late Cretaceous, the continent of North America was divided into two sections: Laramidia in the west and Appalachia in the east. Although the sediments of Appalachia recorded only a sparse fossil record of dinosaurs, the dinosaur faunas of this landmass were different in composition from those of Laramidia. Represented by at least two taxa (Appalachiosaurus montgomeriensis and Dryptosaurus aquilunguis), partial and fragmentary skeletons, and isolated bones, the non-tyrannosaurid tyrannosauroids of the landmass have attracted some attention. Unfortunately, these eastern tyrants are poorly known compared to their western contemporaries. Here, one specimen, the partial metatarsus of a tyrannosauroid from the Campanian Merchantville Formation of Delaware, is described in detail. The specimen can be distinguished from A. montgomeriensis and D. aquilunguis by several morphological features. As such, the specimen represents a potentially previously unrecognized taxon of tyrannosauroid from Appalachia, increasing the diversity of the clade on the landmass. Phylogenetic analysis and the morphology of the bones suggest the Merchantville specimen is a tyrannosauroid of "intermediate" grade, thus supporting the notion that Appalachia was a refugium for relict dinosaur clades.