Dromaeosaurus

Dromaeosaurus was a genus of theropod dinosaur which lived during the Late Cretaceous period (Campanian), about 76 - 72 million years ago, in the western United States and Alberta, Canada. The name means 'running lizard' and is derived from the Greek dromeus (δρομευς) meaning 'runner' and sauros (σαυρος) meaning 'lizard'.

Description

What scientists do know about Dromaeosaurus is that it was a small carnivore, the size of a wolf, about 1.8 m (6 ft) in length and 15 kg (33 lb) in weight. Its mouth was full of sharp teeth and a sharp "sickle claw" on each foot.

Although only a few bones are known from the hindlimb, they indicate that Dromaeosaurus was a powerfully built animal. The presence of feathers in closely related animals makes it extremely likely that it was feathered as well.

Dromaeosaurus had remarkably large eyes and excellent vision. It also probably had a good sense of smell and hearing. Its neck was curved flexible and its jaws were solidly built. The tail was flexible at the base but sheathed in a lattice of bony rods; this allowed it to be carried in a sharply upturned position.

Discovery and later findings

Despite receiving widespread attention in popular books on dinosaurs, and the usage of a complete mounted skeleton cast in museums throughout the world, Dromaeosaurus is surprisingly poorly known from actual fossils. The preparation of the popular cast by the Tyrrell Museum was only made possible by knowledge gained from other dromaeosaurids that have been discovered more recently.

The first known Dromaeosaurus remains were first discovered by paleontologist Barnum Brown during a 1914 expedition to the Judith River Formation on behalf of the American Museum of Natural history. The area where these bones were collected is now part of Dinosaur Provincial Park in Alberta, Canada. The find consisted of a partial skull 9 inches in length and some foot bones. Several other bones, and dozens of isolated teeth, are also known from subsequent discoveries in Alberta and the western United States.

Several species of Dromaeosaurus have been described, but Dromaeosaurus albertensis is the most complete specimen. Additionally, it is apparent that this genus is even rarer than other small theropods, although it was one of the first small theropods described based on reasonably good cranial material.

In 1969 similarities in anatomy between Dromaeosaurus and its relative Deinonychus were first observed. Based on the sickle-claws and commonalities in the skull, a new family, the dromaeosauridae was erected to house these two genera. Since then, many new relatives of Dromaeosaurus have been found.

Paleobiology and diet

Dromaeosaurus differs from most other Dromaeosauridae in having a short, massive skull, a deep mandible, and robust teeth. In these respects Dromaeosaurus resembled the tyrannosaurs. The teeth tend to be more heavily worn than those of its relative Saurornitholestes, suggesting that its jaws were used for crushing and tearing rather than simply slicing through flesh.

It is possible that Dromaeosaurus was more of a scavenger than other small theropods, or it may be that Dromaeosaurus relied more heavily on its jaws to dispatch its prey. It was probably better suited to tackling large prey than the more lightly built Saurornitholestes.

Relationships

The relationships of Dromaeosaurus are unclear. Although its rugged build gives it a primitive appearance, it was actually a very specialized animal. It is usually given its own subfamily, the Dromaeosaurinae; this group is thought to include Utahraptor, Achillobator, Adasaurus and perhaps Deinonychus.

However, the relationships of dromaeosaurs are still in a state of flux. "Dromaeosaurus Morphotype A" is the designation given to a series of unusual, ridged dromaeosaur teeth from Alberta. These teeth probably do not belong to Dromaeosaurus, although it is unclear from what animal they do come.

In popular culture

Dromaeosaurus are featured in Walking with Dinosaurs, stalking juvenile Torosaurus and attempting to steal eggs from Tyrannosaurus.

References

Further reading

• Dixon, Dougal (2006). The Illustrated Encyclopedia of Dinosaurs (Lorenz Books): 200-201.
• Matthew, W. D. and B. Brown (1922). The family Deinodontidae, with notice of a new genus from Cretaceous of Alberta. Bulletin of the American Museum of Natural History 46: 367-385.
• Colbert, E. and D. A. Russell (1969). The small Cretaceous dinosaur Dromaeosaurus. American Museum Novitates 2380: 1-49.
• Currie, P. J., K. J. Rigby, et al. (1990). Theropod teeth from the Judith River Formation of southern Alberta, Canada. Dinosaur Systematics: Perspectives and Approaches. P. J. Currie and K. Carpenter. Cambridge, Cambridge University Press: 107-125.
• Currie, P. J. (1995). New information on the anatomy and relationships of Dromaeosaurus albertensis (Dinosauria: Theropoda). Journal of Vertebrate Paleontology 15(3): 576-591.