One sickle-clawed predator turned plodding dinosaurs into agile, bird-like hunters
Until the late 1960s most people pictured dinosaurs as sluggish, oversized reptiles. Then John Ostrom described Deinonychus, a slim Montana predator with a hooked claw on each foot, and argued it must have been fast and active. His work sparked the dinosaur renaissance and the long argument over whether dinosaurs were warm-blooded.
The name means terrible claw, after the curved talon on the second toe of each hind foot. Ostrom compared crocodile and bird claws to estimate the horny sheath and reconstructed the claw of the type specimen at over 120 millimetres. The animal reached up to 3.4 metres long and lived in North America between about 115 and 98 million years ago, with fossils from Montana, Wyoming, Utah and Oklahoma and possible teeth as far east as Maryland.
Barnum Brown actually found it first, in 1931 near Billings, while digging up the plant-eater Tenontosaurus. He nicknamed the small carnivore Daptosaurus agilis but never finished describing it. A little over three decades later, in August 1964, Ostrom's Yale team began work near Bridger, and the next two summers yielded more than 1,000 bones from at least three individuals. Ostrom formally named the species in February 1969.
Its second name, antirrhopus, means counterbalancing, reflecting Ostrom's view that a tail braced by bony rods acted as a rigid counterweight. A beautifully articulated Velociraptor tail later showed an S-shaped sideways curve, suggesting these tails were more flexible than he thought. Ostrom also mistook a shoulder bone for an oddly shaped pelvic bone until his 1974 study, the same year a Harvard expedition dug up a more complete skeleton with thigh bones and a proper pubis.
Deinonychus teeth keep turning up beside Tenontosaurus skeletons, which implies it hunted or at least scavenged the larger herbivore. That pattern has fed debate over whether it lived alone or in groups; recent evidence leans toward some gregarious behaviour, though not coordinated wolf-style packs. Mounted skeletons stand at the American Museum of Natural History and at Harvard's Museum of Comparative Zoology.
Source: Deinonychus
