|- |(unranked)||Maniraptora

|- |(unranked)||Deinonychosauria

Deinonychus antirrhopus ("fearsome claw") is a wolf-sized, carnivorous dinosaur species from the Early Cretaceous Clovery Formation of Montana. Its name, "fearsome claw", refers to the huge, sickle-shaped talons on the second toe. These claws were probably held retracted while the dinosaur walked on the third and fourth toes. It is thought that Deinonychus would kick with the sickle claws to slash at its prey. The tail was stiffened by a series of ossified tendons, similar to those seen in the tails of some pterodactyls.

Discovery

Based on the association of a number of Deinonychus skeletons in a single quarry — several hundred Deinonychus bones were discovered by John Ostrom and Grant E. Meyer in 1964 in southern Montana — it has been speculated that Deinonychus lived in packs. This is quite possible, but it is difficult to prove or disprove this idea. Shed teeth of Deinonychus are often found alongside skeletons of the ornithopod dinosaur Tenontosaurus , indicating that it fed on them, and perhaps hunted them.

Paleontologist John H. Ostrom named and described Deinonychus, and the discovery of this clearly active, agile predator did much to change the scientific (and popular) conception of dinosaurs and open the door to speculation that dinosaurs may have been warm blooded. Several years later, Ostrom noted similarities between the hand of Deinonychus and birds, which led him to revive the hypothesis that birds are descended from dinosaurs. Thirty years later, this idea is almost universally accepted. Finds of related dinosaurs from China, such as Sinornithosaurus and Microraptor indicate that this dinosaur probably bore feathers. Other relatives include Velociraptor, Utahraptor, and Dromaeosaurus. A skeleton of Deinonychus can be seen on display at the American Museum of Natural History or the Harvard Museum of Comparative Zoology. The American Museum and Harvard specimens are from a different locality than the Yale specimens which Ostrom described, and the claws are different shapes (Ostrom 1976). This raises the possibility that the two are, in fact, different species or even different genera.

• Skull length: 410 mm (16 in)
• Total length: 3 m (10 ft)
• Hip height: 1.2 m (4 ft)
• Weight: 80 kg (175 lb)

References

• Maxwell, W. D. and J. H. Ostrom (1995). "Taphonomy and paleobiological implications of Tenontosaurus-Deinonychus associations." Journal of Vertebrate Paleontology 15(4): 707-712.

• Norell, M. A. and P. J. Makovicky (2004). Dromaeosauridae. The Dinosauria. D. B. Weishampel, P. Dodson and H. Osmolska. Berkeley, University of California Press: 196-209.

• Ostrom, J. H. (1969). "Osteology of Deinonychus antirrhopus, an unusual theropod from the Lower Cretaceous of Montana." Peabody Museum of Natural History, Bulletin 30(1-165).

• Ostrom, J. H. (1976). "On a new specimen of the Lower Cretaceous theropod dinosaur Deinonychus antirrhopus." Breviora 439: 1-21.

• Ostrom, J. H. (1976). "Archaeopteryx and the origin of birds." Biological Journal of the Linnean Society 8: 91-182.