Deinonychus antirrhopus Ostrom 1969
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The bones of the foot of Deinonychus showing the location of the ungual bone of digit 2 (after Ostrom 1969).
Reconstruction of Deinonychus showing the location on the skeleton of the ungual bone that was cast for this reproduction -after Ostrom 1969

Systematics: Saurischia, Theropoda, Dromeosauridae, Deinonychus antirrhopus

Adult size: Length 8 to10 feet (2.5 to 3.5 meters); height 3 to 4 feet (about 1 meter); weight 130 to 165 lbs (60 to 75 kilograms)

Catalog no.: YPM 5205

Etymology: deinos meaning “terrible” and onyx meaning “claw”, antirrhopus meaning “counterbalancing” (Greek)

Age: Cloverly Formation, Early Cretaceous (110 to 115 million years ago)

Locality: Carbon County, Montana, USA

Collector: John H. Ostrom, Cloverly Expedition, 1964–1965

Some discoveries in science completely change our ideas about our world. We once believed that extinct dinosaurs were like giant, sluggish lizards. Then in 1969 Yale University’s John H. Ostrom described Deinonychus (“terrible claw”), a fossil skeleton he unearthed some five years earlier in Montana. The description of this animal sparked a controversy that caused scientists to rethink their lazy-lizard ideas about dinosaurs. The images of athletic, intelligent dinosaurs that we see today in movies and on television have their origins in the discovery and description of Deinonychus.

This animal was a totally new kind of dinosaur—obviously fast, agile and intelligent, and armed with fearsome claws used to slash and disembowel its victims. Its hands were well adapted to grasping and could have held prey while the sickle-like claws did their deadly work. This small theropod of the Early Cretaceous was the North American cousin of Velociraptor. Fossil evidence suggests that Deinonychus may have hunted in packs and was not shy about taking on creatures five to six times its size.

In addition to being a very active predator, Deinonychus shares some important characteristics with the living dinosaurs—birds. Imagine the excitement of being the first to discover this vital connection between extinct dinosaurs like Deinonychus and the living, feathered flying animals we see today. Deinonychus had five toes, but like all bipedal theropods it stood on only three of them. We know this because theropod footprints show a characteristic three-toed stance, like those of modern birds.

Deinonychus means “terrible claw,” and this cast of the ungual is just that. The last bone in the second toe, it was covered by a sharp, horn-like claw that was used to slash and disembowel victims. This cast is made from a specimen found during John Ostrom’s 1964 Yale University expedition to Montana. Two casts of the full skeleton and a reconstruction of the animal as it may have looked in life are on display in the Peabody Museum of Natural History’s Great Hall.