English: Deinonychus tooth fossil, found with a Tenontosaurus prey victim, on display in the Museum of the Rockies in Bozeman, Montana. (It is not clear where the specimens in this display were collected.)

A synonym for Deinonychus is the more familiar Velociraptor (made famous by the Jurassic Park movies).

Deinonychus antirrhopus was first discovered in 1931 near Billings, Montana. Its name means "terible claw", because it could lift the middle toe of its heavily clawed foot and slice with it like a razor.

In the late 1960s, paleontologist John Ostrom published a series of papers about Deinonychus that completely revolutionized the way we think about dinosaurs. Previously, scientists thought of them as plodding, slow, cold-blooded creatures. But Ostrom proved that Deinonychus couldn't be cold-blooded, and was undoubtedly lightning-fast and very agile. Within just a few years, everyone accepted that dinosaurs had to be warm-blooded, and most were extremely active and mobile. This was the "Dinosaur Revolution" or "Dinosaur Renaissance", and it governs the way we think about dinos today.

Deinonychus lived 115 to 108 million years ago in western North America. It was about 11 feet in length, and tended to run with its head lowered and tail stuck straight out as a counterbalance. In this position, it was only about three feet high at the hip. It weighed no more than 160 pounds. The 16-inch-long skull had 70 curved, blade-like teeth in a very narrow snout and it had stereoscopic vision. Deinonychus had strong forelimbs, powerful and very large hands, and three claws on each hand. The middle of the three toes on each hind foot had a sickle-shaped claw. The snap-tendons on that toe permitted it to be used like a scythe!

Deinonychus was originally thought to be like most dinos -- reptilian and hairless. But since ancestors and close relatives of Deinonychus had feathers, it is bellieved that Deinonychus did as well.

Tenontosaurus (the "sinewy lizard") is a primitive Iguanodont that lived in western North America about 115 to 108 million years ago. Fossils were first discovered in Big Horn County, Montana, in 1903. Tenontosaurus was about 21 to 26 feet long and 10 feet high when it stood upright. (It usually traveled on all fours, however.) It weighed aboout one to two tons. Its tail was unusually long and broad, and the tail and the back was stiffened with a network of bony tendons (hence the name).

Tenontosaurus was incredibly common, and Deinonychus preyed on it heavily.

This tooth was found in the Tenontosaurus skeleton, proving that Deinonychus preyed on these herbivores.