Deinonychus was a spectacular, but fairly small dinosaur. It was a fast and vicious hunter. Its name means "terrible claw," and it was given this name because of the large, retractable hunting claw on each of its feet. Like its cousin, the Velociraptor, it used this claw to tear into the flesh of the dinosaurs it hunted. The claw would snap forward and make a large, deep wound when it attacked. Deinonychus was about twice as big as Velociraptor.  Shed teeth and several specimens of Deinonychus were found with the skeleton of a large plant eating dinosaur, Tenontosaurus. Some  authorities maintain that this established that they hunted in packs, ones capable of bringing down animals much larger than themselves.
   Deinonychus belongs to a family of dinosaurs called dromaeosaurs. They all share the same characteristics a lightly built skull with sharp backwardly curved teeth, elongated arms and hands with sharp claws, and an extraordinary sickle-like second toe claw which was carried raised off the ground to protect the sharp point. Dromaeosaurs probably had keen vision and their brains were relatively large for a dinosaur. The dromaeosaurs lived throughout the Cretaceous period, 140 to 65 million years ago.
   In his 1986 book The Dinosaur Heresies, Dr. Robert Bakker puts forth the view that Deinonychus has many features found in birds and might be considered either a bird-like dinosaur or a dinosaur-like bird. Recent research and discoveries by scientists such as Dr. Philip Currie are showing that some dinosaurs similar to Deinonychus most likely had feather-like coverings on all or part of their bodies. These proto-feathers were most likely used for insulation, display, or both, and may eventually have evolved into flight feathers. To date, these have not been found on Deinonychus. 
   Several hundred Deinonychus bones were discovered by paleontologist John Ostrom and Grant E. Meyer in 1964 in southern Montana  John 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.
   Deinonychus is probably the best known of the dromeasaurids as nine specimens have been discovered 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.