How Deinonychus Upended the Way We Look at Dinosaurs

While exploring southern Montana in 1931, paleontologist Barnum Brown found the incomplete skeleton of an 8-foot (2.5-meter) dinosaur. Clearly, it was a theropod, a member of the same group as Allosaurus and Tyrannosaurus rex.

This one had an agile build. Not only was it light-boned, but there were long, wiry extensions on the tail vertebrae. Brown guessed these stiffened the appendage as a whole, helping the tail act as a better counterweight to the rest of the body.

Though Brown planned to write a manuscript about the intriguing new dinosaur, he was unable to finish it before his death in 1963. But in his later years, Brown showed the skeleton to a young researcher named John Ostrom.

August 1964 found Ostrom hunting for early Cretaceous dinosaurs around Bridger, Montana. Under the summer sun, he and a colleague discovered the clawed hand of a theropod peaking out of the earth. Then a foot turned up. So did thousands of other bones.

Ostrom soon realized he was dealing with the same species as the one Brown unearthed decades earlier. He named the creature Deinonychus antirrhopus in 1969. At the time, he'd recovered the bodies of four individuals at a single Montana quarry — all lying in close proximity to some Tenontosaurus bones.

Deinonychus, the theropod's genus name, means "terrible claw." This was inspired by the huge curved claws that topped the second toe of each foot.

To Ostrom, the weapons were a revelation. Deinonychus would've held these claws high off the ground as it walked. Historically, dinosaurs were imagined to be slow and lethargic. Yet Deinonychus contradicted this assumption. With its light bones and battle-ready toe claws, the creature obviously led an athletic lifestyle.

"It must have been a fleet-footed, highly predaceous, extremely agile and very active animal, sensitive to many stimuli and quick in its responses," wrote Ostrom in 1969.

Today, the 1970s and late 1960s are fondly remembered as the "Dinosaur Renaissance." There was a sudden surge of exciting new discourse about our favorite prehistoric beasts. The idea that birds descend from dinosaurs, now a scientific consensus, gained new traction at this time. Meanwhile, old beliefs regarding dinosaur metabolic rates came into question.

Ostrom's work on Deinonychus was a catalyst for the renaissance. But you don't have to be a science enthusiast — or a history buff — to appreciate its impact.

Ever hear of "Jurassic Park?" We hate to say it, but John Hammond (Richard Attenborough's character) lied to you. The dinosaur that's called Velociraptor in those movies was really based on Deinonychus.

Don't get us wrong. There was an actual theropod named Velociraptor that lived in Central Asia 75 to 71 million years ago. However, it was way smaller than the monsters shown in "Jurassic Park" and its sequels. The "raptors" of those films can look a grown man in the eye. Standing just 28 inches (72 centimeters) tall at the hip, the real Velociraptor was a pipsqueak by comparison.

Deinonychus couldn't quite measure up to the Hollywood raptors, either. At least it was bigger than the turkey-sized Velociraptor. We now know John Ostrom's "extremely agile and very active animal" grew more than 11 feet (3.3 meters) long, with a hip height of 3.2 feet (1 meter).

Both Velociraptor and Deinonychus belonged to the same family of theropods: the dromaeosaurs. Found in Eurasia, Africa and the Americas, the dromaeosaurs had knife-like teeth, big skulls and long limbs. At least some (probably all) of them rocked feathers to boot.

Let's revisit those terrible claws. Deinonychus wasn't unique in having an enlarged talon on the second toe of each foot. It's a standard dromaeosaur feature. Said toes were hyperextensible; they could be pulled back into an almost vertical position.

Besides keeping the claw tips sharp, this trait gave them a wide arc of motion. Ostrom imagined his Deinonychus leaping through the air, slashing wildly with the curved daggers on its flexible toes.

Computer modeling paints a different picture. Paleontologist Peter J. Bishop published a 3D Deinonychus hindlimb reconstruction in a 2019 paper. According to his simulations, the dreaded toe claws couldn't exert very much force — and they were probably better at grasping prey than disemboweling it.

Dromaeosaur tails also warrant a closer look. Remember the long rods on Deinonychus' tail vertebrae? Velociraptor, Utahraptor and other dromaeosaurs had those, too. At first, experts thought they made all but the base of the tail very rigid — sort of like a tightrope walker's balancing pole.

This was contradicted by the 1999 discovery of a Velociraptor skeleton with a curled tail. Time and time again, the dromaeosaurs subvert our expectations.

There's one last thing we should mention. Tenontosaurus, by John Ostrom's reckoning, might've been five or six times heavier than Deinonychus. Seeing four carnivores — all of the same species — clustered around a much bigger plant-eater got him thinking.

"The multiple remains ... suggest that Deinonychus may have been gregarious and hunted in packs," wrote Ostrom in '69.

Author Michael Crichton ran with the idea. His original "Jurassic Park" novel, the basis for Stephen Spielberg's movie, describes the "raptors" attacking their prey in organized packs. The film series more or less follows suit.

Yet scientists have cause for skepticism. Habitual, strategic pack-hunting is quite rare among modern animals. Perhaps Deinonychus and other dromaeosaurs were loners for the most part, but went into spontaneous group feeding frenzies now and then (that's how Komodo dragons roll).