Deinonychus is a genus of carnivorous dromaeosaurid dinosaurs. There’s one described species, Deinonychus antirrhopus. These dinosaurs, which were capable of growing to be 11 ft long, lived during the early Cretaceous Period, around 115 to 108 million years ago. Fossils have been uncovered from the U.S states of Wyoming, Montana, and Oklahoma, in rocks of the Cloverly Formation and Antlers Formation, though teeth that might belong to Deinonychus have been found much farther east in Maryland.

John Ostroms study of Deinonychus revolutionized the way scientists thought about dinosaurs. His study led to the “dinosaur renaissance” and awoken the debate on whether dinosaurs were warm-blooded or cold-blooded. Before this, the accepted concept of dinosaurs had been one of plodding, reptilian giants. Ostrom noted that the body was small, the posture sleek and horizontal, the spine ratite-like, and particularly the enlarged raptorial claws on the feet, which proposed an active and agile predator.

Deinonychus had an unusually large and sickle-shaped talon on the second toe of each hind foot. In both the Antlers and Cloverly Formations, Deinonychus remains have been found closely associated with the remains of the ornithopod Tenontosaurus. Some teeth uncovered associated with Tenontosaurus samples entail that they were hunted, or at least scavenged upon, by the Deinonychus.

Based on largest known specimens, Deinonychus was able to reach at least 11 ft 2 in long, with a skull length of 16.1 inches, a hip height of 2 ft 10 in, and an estimated weight of 160 lb. The skull was outfitted with strong jaws that were lined with around 70 curved teeth similar to a blade. Studies of the skull have advanced over the decades. Ostrom rebuilt the partial, imperfectly preserved skulls that he had as broad, triangular, and quite similar to Allosaurus. Additional skull material and closely related species that were uncovered with good three-dimensional preservation illustrate that the palate was more domed than Ostrom though, making the snout narrower, while the juguls flared widely, giving better stereoscopic vision. It was different than that of Velociraptor, however, in that it had a healthier skull roof, similar to that of Dromaeosaurus, and didn’t have the depressed nasals of Velociraptor. Both the lower jaw and skull had fenestrae, meaning skull openings, which decreased the weight of the skull. In Deinonychus, the antorbital fenestra, an opening between the eye and the nostril, was especially large.

It possessed large “hands” with three claws on each of the forelimbs. The first digit was the shortest and the second was the longest. Each hind foot bore a sickly-shaped claw on the second digit, which was mostly likely put to use during predation. No skin impressions have been found regarding Deinonychus. Nonetheless, evidence suggests that the Dromaeosauridae, which includes Deinonychus, had feathers.

Deinonychus antirrhopus is none of the most popular dromaeosaurid species, and a close relative of the smaller Velociraptor, found in younger, Late Cretaceous-age rock formation in Central Asia.

Remains of Deinonychus have been uncovered from the Cloverly Formation of Wyoming and Montana and in the roughly contemporary Antlers Formation of Oklahoma, North America. Initial remains were uncovered in 1931 in southern Montana close to the town of Billings. A little more than 30 years later, in August 1964, John Ostrom led an expedition from Yale University’s Peabody Museum which uncovered more skeletal material close to Bridger. Expeditions during the following two summers uncovered more than a thousand bones including at least three individuals.

In the Cloverly Formation, Deinonychus teeth found in association with some fossils of the ornithopod dinosaur, Tenontosaurus are quite frequent. A study in 2007 has called into question the cooperative pack hunting behavior of Deinonychus, stemming from what is already known about modern carnivore hunting and the taphonomy of tenontosaur sites. Bite force estimates were first produced in 2005, based on reconstructed jaw musculature. The study concluded that it was likely that Deinonychus had a maximum bite force only 15 percent of that of the modern American Alligator. A 2010 study attempted to estimate the bite force based directly on newly uncovered Deinonychus tooth puncture marks in the bones of a Tenontosaurus. The puncture marks came from a large individual, and produced the first evidence that a large Deinonychus had the ability to bite through bone. Utilizing the tooth marks, scientists were able to conclude that the bite force of Deinonychus to be between 4,100 and 8,200 newtons, greater than living carnivorous mammals.

Despite being the most unique feature of Deinonychus, the shape and curving of the sickle claw is variable between specimens. The type specimen has a strongly curved sickle claw, while a more recent specimen had a claw with a much weaker curve, more similar in shape with the ‘normal’ claws on the other toes. Ostrom proposed that this difference in the shape and size of the sickle claws could be a result of individual, age related, or sexual variation.

Image Caption: Skeleton of the dromaeosaurid dinosaur Deinonychus at Field Museum of Natural History. At the bottom is the skeleton of Buitreraptor. Credit: AStrangerintheAlps/Wikipedia (CC BY-SA 3.0)