Deinonychus was a carnivorous dinosaur that lived during the Cretaceous period, between about 100 and 110 million years ago. It is a fairly well studied dinosaur, with several nearly complete skeletons having been found. It is a member of the Dromaeosaurid class of dinosaurs, which also includes Dromaeosaurus and Velociraptor. It was about 3 meters in length, but probably did not stand as high as an average person. Paleontologists estimate its weight at about 70 kilograms. All known examples have been found in North America.
The skull of Deinonychus is lightly built, with large openings for the eyes, two characteristics of modern predators. The teeth are serrated, and point toward the back of the skull, which would have allowed the animal to tear off great chunks of flesh from its prey.
The arms are long and end in large, three fingered hands equipped with very large, curved talons. Together with the broad upper arm bone, with its roughened attachment points for what must have been very powerful chest muscles, this indicates that they were used to catch and hold prey.
The name Deinonychus means “terrible claw” and comes from the beast’s most striking feature, a giant claw on the second toe of its hind legs. The claw is articulated on an abnormally large joint, which would have allowed the animal to hold it clear of the ground when running, to protect the point. Deinonychus likely used the claw as its main weapon, slicing it into its victim while holding onto the prey with its powerful arms and jaws. The hind leg itself was very powerfully built and Deinonychus was likely a fast runner.
The tail is also interesting, being stiffened by a series of overlapping, bony rods. This would have allowed the dinosaur to hold the tail very stiff while running, as a counterbalance for its upper body, and possibly to assist it in making sharp turns.
Deinonychus was a relatively small predator, living at the same time as giant Sauropods, and some scientists speculate that it may have hunted in packs, much like wolves, preying on the young or injured of these giants. Others hypothesize that it hunted alone, like today’s big cats.
All in all, Deinonychus was surely one of the most unusual and spectacular predators that ever lived.
Note: The 'Velociraptors' featured in Steven Spielberg's Jurassic Park are actually closer in size and appearance to Deinonychus than to the actual Velociraptor remains that have been discovered.