Among the dinosaurs, the Dromaeosaurids or Dromaeosauridae ("running lizards") were fast and agile dominant carnivores throughout the Cretaceous period. In popular usage they often called "raptors" after the Velociraptor, which was made famous by the film Jurassic Park.

Dromaeosauridae have been found in North America, Europe, North Africa, Japan, China, Mongolia and Argentina. They were a very successful group in the Cretaceous, existing for over 60 million years, up until the Cretaceous-Tertiary extinction event.

Characteristics

The characteristics of the Dromaeosauridae are distinctive. Unlike their close relatives, such as Troodon, dromaeosaurids were muscular animals. Long fleshy tails held out behind could help them swing quickly to change direction. They were lightly built, agile, bipedal hunters, with large eyes. They also had the biggest brains for their body weight among all dinosaurs, with an encephalization quotient of about 5.0¹, which indicates that they were among the most intelligent dinosaurs. They were far more intelligent than the plant-eating sauropods, with their intelligence perhaps approaching that of modern-day birds of comparable sizes (Hopson 1980).

There is evidence that some dromaeosaurids hunted in packs: Deinonychus fossils have been uncovered in small groups that seem to have been killed while attacking Tenontosaurus tilletti, a larger ornithischian dinosaur. Not all paleontologists find the evidence conclusive, however.

The enlarged "killer claw" possessed by some dromaeosaurids (Deinonychus means "terrible claw") was a raking weapon that could open a deep disembowelling gash. Then the agile predator could withdraw and wait for a victim to weaken from bleeding.

Relationship with birds

Main article: Feathered dinosaurs.

Dromaeosaurids are theropods, and may be the sister taxon to Avialae (birds). Dromaeosauridae is a subgroup of Deinonychosauria, and includes such animals as Deinonychus, Dromaeosaurus, Velociraptor, Saurornitholestes, and Utahraptor.

Recently described Chinese "dromaeosaurs", such as Microraptor, Cryptovolans and Sinornithosaurus had modern pennaceous feathers and fully formed remiges or "flight feathers", leading to the question of whether these animals were capable of powered flight.

Discussion about the relationship between birds and dinosaurs has mostly narrowed to whether bird ancestors lie within Dromaeosauridae or not. In order to exclude them, one recent cladistic analysis (Senter 2004) has gone so far as to remove these three genera from Dromaeosauridae in the strict sense, and the authors created a new closely related taxon Microraptoria for them. Thus under this re-classification, it can still be claimed that there have been no reports of fossil feathers in Dromaeosauridae.

In fiction

Velociraptor made a memorably chilling villain in the movie Jurassic Park, although it was enlarged far beyond its actual size. While the movie was in production, the discovery of Utahraptor confirmed that such giant Dromaeosaurids did in fact exist.

References

• Hopson, J. A. 1980, "Relative brain size in dinosaurs: implications for dinosaurian endothermy", American Association for the Advancement of Science Symposium no. 28, pp. 287–310.
• Senter, P., R. Barsold, B.B. Britt and D.A. Burnham. 2004. "Systematics and evolution of Dromaeosauridae (Dinosauria, Theropoda)" in Bulletin of the

Gunma Museum of Natural History, 8: 1-20.

External links

• The Dromaeosauridae: The Raptors! (http://www.ucmp.berkeley.edu/diapsids/saurischia/dromaeosauridae.html), from the University of Calfornia Berkeley Museum of Paleontology.
• Dromaeosauridae (http://personal2.stthomas.edu/jstweet/dromaeosauridae.htm), by Justin Tweet from Thescelosaurus!