New information on the anatomy and relationships of Dromaeosaurus albertensis (Dinosauria: Theropoda)

ABSTRACT

Dromaeosaurus albertensis was one of the first small theropods described that was based on reasonably good cranial material. It was realized from the beginning that this animal was significantly different from other Cretaceous theropods, and the Dromaeosauridae was created for its inclusion. In the intervening years, a number of genera were assigned to this family, which came to assume an important position in discussions on theropod relationships and evolution, and the origin of birds. It is now known that many of the dromaeosaurids are different enough from Dromaeosaurus to be included in a distinct subfamily known as the Velociraptorinae. In spite of intensive collecting activity, the holotype of Dromaeosaurus albertensis is still the most complete specimen, and it is apparent that this genus is even rarer than other small theropods. Repreparation and restudy of the holotype has produced new anatomical information useful for evaluating the relationships of dromaeosaurids. Contrary to previous reports, the premaxillary teeth are not D-shaped in section, the cranium is not pneumatic, there are interdental plates, and the braincase bones are not pneumatized. Dromaeosaurids form a distinct clade of specialized, successful theropods that are not closely related to other “coelurosaurs” of the Late Cretaceous.