Dromaeosaurus (“running lizard”) was a genus of theropod dinosaur which lived during the Late Cretaceous period (middle late Campanian), sometime between 76.5 and 74.8 million years ago, in the western United States and Alberta, Canada. The type species is Dromaeosaurus albertensis, which was described by William Diller Matthew and Barnum Brown in 1922.
One feature common to all dromaeosaurids was the extreme stiffness of their tails. The tails of most theropods were stiffened, at least for part of their length. This relative inflexibility was caused by the lengthening of the attachment processes (bony rods known as zygapophyses) on the vertebrae. In the dromaeosaurids, however, these rods became greatly elongated, each of them extending over several vertebrae and effectively bracing them together. As a result of this, the thin tails of the dromaeosaurids became completely inflexible. The stiff tail would have helped Dromaeosaurus in pursuing prey by acting as an effective counterbalance behind the hip.
Dromaeosaurus was a small carnivore, about 2 m (6.6 ft) in length and 15 kg (33 lb) in weight. Its mouth was full of sharp teeth, and it had a sharply curved “sickle claw” on each foot. It lived during the Campanian stage of the Late Cretaceous, however, some fragmentary remains such as teeth which may belong to this genus have been found from the late Maastrichtian age Lance and Hell Creek Formations, dating to 66 million years ago. Teeth have also been found in the Aguja Formation.
The exact relationships of Dromaeosaurus are somewhat unclear. Although its rugged build gives it a primitive appearance, it was actually a very specialized animal. In analyses of the present clade Dromaeosaurinae species as Utahraptor, Achillobator and Yurgovuchia are often recovered. As of recently, the genus Dakotaraptor has been classified as the sister taxon to Dromaeosaurus.