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die - NON - oh - ee - kus

Todd Marshall. Copyright 2007

Field Notes

Name Means: "Terrible claw"
Length: 10 feet (3 m)
Diet: Carnivore (Meat-Eater)
Time: Early Cretaceous
Location: Montana, Wyoming, Oklahoma, USA

Although it was not the first of the dromaeosaurs to be discovered, Deinonychus, which was one of the largest of them, was the first to be fully described. After it was described, the dromaeosaurids, which are now improperly known as "raptors," became recognized as some of the most chillingly efficient predators that have ever lived.

Deinonychus was an agile bipedal theropod with large, partly forward-facing eyes, a relatively large brain, and a long, narrow snout lined with recurved, serrated, bladelike teeth. Deinonychus was an inteeligent, very well-equipped predator that used the three long-clawed fingers on each of its large hands to snatch small prey or to inflict terrible wounds on large animals. It may also have employed its claws as grappling hooks to clamber up on the bodies of larger dinosaurs that it hunted and attacked in packs.

Deinonychus walked, ran, and jumped mainly on the outer (third and fourth) toes of each foot. These toes had long, sharp claws. The first toe was also clawed but this claw was quite short. The claw on the second toe was, by contrast, an extra-large, curved slashing weapon up to 5 inches (13 cm) long that was able to swivel through 180 degrees. Deinonychus usually held this claw back off the ground in order to keep the point sharp, loaded, and "cocked" ready to go in for the kill.

As in many other dinosaurs, the tail of Deinonychus was stiffened for about three-quarters of its length by bundles of overlapping bony rods, which, however, were flexible at the base. This stiffening allowed the tail to be controlled by a few large muscles that connected to the hips and hindlimbs. It helped Deinonychus to make rapid lunges or to change direction suddenly when running - Deinonychus may even have been able to turn around in mid-air while leaping to catch prey. It also prevented the tail from flexing from side to side in time with the limb movements while the animal was running, thus preventing energy from "leaking away" into the tail and helping the dinosaur to run faster and more efficiently.

Grant Meyer and Professor John Ostrom of Yale University first discovered remains of Deinonychus in southern Montana in 1964. Excavation at this site produced remarkable finds - nearly complete skeletons of four Deinonychus, together with a skeleton 20 feet (6 m) long of the Iguanadon-like ornithopod Tenontosaurus. When Ostrom described and named Deinonychus in 1969, he suggested that Tenontosaurus was its preferred quarry and that this association of predators and prey was evidence for pack hunting behavior in Deinonychus. Certainly a single Deinonychus would not have been capable of killing a herbivore as large as Tenontosaurus, though the death of four Deinonychus in the attack could hardly be considered typical.

If, as seems probable, Deinonychus did live in packs and hunted much larger dinosaurs, it must have been similar in behavior and ecology to present-day wolves, hunting dogs, and hyenas. This implies that Deinonychus was not only an acrobatic predator with an armory of deadly weapons, but also an endurance athlete - and one that existed, probably, as part of a caring, cooperative social group.

Territories near the migration routes or breeding sites of large herbivores could have supported large packs of 20 or more Deinonychus, dominated by a few breeding individuals. Non-breeding adults would have defended the territory from rival groups of Deinonychus and other carnivores, and they would also have helped to feed the young of the dominant breeding animals.

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