Deinonychus antirrhopus die-NON-ih-kuss

"Terrible claw"

Deinonychus silhouette — silhouette · Manabu Sakamoto (CC-BY) via PhyloPic

Length: 3.4 m (11.2 ft) — About 3.4 m long, ~75 kg — wolf-sized.
Period: Early Cretaceous (115–108 Mya)
Place: North America · Montana · Wyoming · Oklahoma
Food: Carnivore — Medium-sized prey, including Tenontosaurus, an ornithopod 5–6 times its weight.
Clade: Dromaeosauridae Dinosauria Saurischia Theropoda Coelurosauria Sickle-clawed raptors: Velociraptor, Deinonychus, Utahraptor.

The "terrible claw" raptor whose study sparked the dinosaur renaissance.

Deinonychus is the dinosaur that changed everything. When John Ostrom dug up its skeleton in 1964, the long arms and sickle claw made him realize dinosaurs were warm-blooded, active animals — not slow swamp reptiles. He even predicted feathers on these animals, decades before they were found. The ‘raptors’ from Jurassic Park are really Deinonychus with the name borrowed from Velociraptor.

More about Deinonychus

Discovery

Named by John Ostrom · late 1960s · Cloverly Formation of Montana and Wyoming, and the Antlers Formation of Oklahoma, in North America

The first remains were uncovered in 1931 near Billings, Montana, by a team led by Barnum Brown, who was mainly excavating a Tenontosaurus and only informally noted the small carnivore. In August 1964 John Ostrom led a Yale Peabody expedition that recovered the material he later studied and named.

The name means "terrible claw" and refers to the unusually large, sickle-shaped talon on the second toe of each hind foot. The species name antirrhopus means "counter balance".

John Ostrom. The paleontologist whose study of Deinonychus in the late 1960s revolutionized how scientists thought about dinosaurs, helping launch the dinosaur renaissance and igniting the debate over whether dinosaurs were warm-blooded or cold-blooded.

Was the famous stiff, balancing tail real?

The species name antirrhopus ("counter balance") reflects Ostrom's idea that the tail acted as a stiff counterbalance, supported by ossified tendons and elongated bone processes on the tail vertebrae. However, an articulated tail of the very closely related Velociraptor (IGM 100/986) is curved laterally in a long S-shape, which suggests the tail could in fact bend to the sides with a high degree of flexibility.

For the curious → Is Deinonychus a velociraptorine or a dromaeosaurine?

Its placement is debated. A 2015 analysis classified Deinonychus as a member of Dromaeosaurinae, while a 2021 study of Kansaignathus instead recovered it as a velociraptorine, intermediate between more basal forms and Velociraptor. As a dromaeosaurid, it sits among the non-avialan dinosaur groups most closely related to birds.

What we know

Discovered in 1964 by John Ostrom — the find that triggered the 'Dinosaur Renaissance'.
Sickle claw on the second toe, much larger than Velociraptor's.
Long stiff tail used as a counterweight for balance during fast turns.
Found near Tenontosaurus skeletons with shed teeth nearby — evidence it ate or scavenged them.

What we guess

Whether Deinonychus hunted in packs. Multiple skeletons near one Tenontosaurus suggest yes, but they could have been competing scavengers.
How the feathers looked — likely large wings on the arms even though it couldn't fly.
Whether sickle claws were used for slashing, climbing, or pinning prey.