Deinonychus and the Dinosaur Renaissance: Ostrom's 1964 Find

Deinonychus is a mid-sized predatory dinosaur from the Early Cretaceous of North America, discovered by the Yale palaeontologist John Ostrom in Montana in 1964 and named in 1969. Its agile build and huge sickle-shaped toe claw convinced Ostrom that at least some dinosaurs were fast, active animals. The find launched the “Dinosaur Renaissance” and revived the idea that birds evolved from dinosaurs.

Background: dinosaurs as sluggish reptiles

For much of the twentieth century dinosaurs were usually portrayed as slow, cold-blooded reptiles that dragged their tails and lumbered through swamps. Many scientists regarded them as an evolutionary dead end, outcompeted at the end of the Cretaceous.

The question of bird origins had also stalled. In the 1860s Thomas Henry Huxley had argued that birds were closely related to dinosaurs, partly on the basis of Archaeopteryx. But an influential 1926 book by Gerhard Heilmann concluded that dinosaurs lacked collarbones and so could not be bird ancestors, and that view dominated for decades.

What happened in 1964

In August 1964 John Ostrom, of Yale University’s Peabody Museum, was prospecting with his assistant Grant E. Meyer in the Cloverly Formation near Bridger, Montana. They spotted a large claw and other bones weathering out of a slope. Excavations in 1964 and 1965 recovered more than a thousand bones belonging to at least three individuals, together with remains of the plant-eating dinosaur Tenontosaurus.

The rocks are of Early Cretaceous age, usually dated to roughly 115 to 108 million years ago. Fragments of the same animal had in fact been collected in the same formation by Barnum Brown of the American Museum of Natural History in 1931, but Brown never formally described them.

In 1969 Ostrom named the animal Deinonychus antirrhopus, meaning “terrible claw” and “counterbalancing”, and published a detailed monograph on its skeleton.

What the skeleton showed

Deinonychus was about 3 to 3.4 metres long and probably weighed between 60 and 100 kilograms. Its most striking feature was a sickle-shaped claw on the second toe, about 12 centimetres long, which was held off the ground while walking.

Ostrom argued that a predator using such a claw must have been agile enough to stand on one leg, kick and slash. Its long arms ended in grasping three-fingered hands. The tail was stiffened by long bony rods, which Ostrom interpreted as a dynamic counterbalance for rapid movement.

From these features Ostrom concluded that Deinonychus was an active, energetic animal. He suggested that such a lifestyle was hard to reconcile with a sluggish reptilian metabolism, raising the possibility that some dinosaurs were warm-blooded. His student Robert Bakker drew a famous running reconstruction for the 1969 monograph, showing the animal as a lithe, sprinting hunter.

From Deinonychus to birds

In 1970 Ostrom examined a fossil in the Teylers Museum in Haarlem, the Netherlands, that had been catalogued as a pterosaur. He recognised it as a specimen of Archaeopteryx. Struck by the similarities between Archaeopteryx and Deinonychus, especially in the wrist, hands and shoulder, he revived Huxley’s argument.

In 1973 Ostrom published “The ancestry of birds” in Nature, followed by a series of detailed papers in the mid-1970s. He argued that birds descended from small theropod dinosaurs similar to Deinonychus. The idea met resistance at first but gradually became the scientific consensus, especially after the discovery of feathered dinosaurs in China from 1996 onwards.

Key people

John Ostrom (1928–2005) found and described Deinonychus and revived the dinosaur origin of birds. Grant E. Meyer was his field partner at the Montana site. Robert Bakker, Ostrom’s student, became the most outspoken champion of warm-blooded dinosaurs; his 1975 Scientific American article “Dinosaur Renaissance” gave the movement its name. Barnum Brown had found the first, undescribed fragments in 1931.

Consequences: the Dinosaur Renaissance

From the 1970s onwards, dinosaurs were increasingly reconstructed as active animals with upright postures, held-up tails and rapid growth. Studies of bone tissue showed that many dinosaurs grew quickly, more like birds and mammals than modern reptiles.

The specific claim of full warm-bloodedness has since been refined. Many researchers now think dinosaur metabolism varied between groups, with small feathered theropods likely close to birds, while others may have been intermediate. The broad picture of dinosaurs as dynamic animals, however, has endured.

The new image reached the public through books and films. The large “raptors” of Jurassic Park (1993) were based in size and appearance on Deinonychus, although they carried the name of the smaller Asian Velociraptor, best known from the Fighting Dinosaurs fossil.

Myths and facts

Myth: Deinonychus disembowelled prey with its claw. Ostrom pictured the claw as a slashing weapon. A 2006 study using a mechanical model of a closely related dromaeosaur claw found it better suited to piercing and gripping than to slicing open large prey, and a 2011 study suggested such claws were used to pin down smaller animals, much as hawks and eagles do.

Myth: Deinonychus hunted in proven packs. Multiple individuals were found with Tenontosaurus remains, but whether they cooperated like wolves or gathered at a kill like Komodo dragons is still debated.

Fact: Deinonychus was probably feathered. No feathers have been found with its fossils, but its close relatives preserve feathers or quill knobs, so most scientists reconstruct it with a feathered body.

Legacy and later research

Deinonychus belongs to the dromaeosaurids, a family of feathered theropods that also includes Velociraptor and Microraptor. Discoveries since the 1990s, particularly in China and Mongolia, have shown that this family was widespread and diverse, ranging from crow-sized gliders to animals several metres long. Each new find has reinforced the anatomical links that Ostrom first traced between Deinonychus and birds.

Later work on the Montana material has added detail. In 2006 Gerald Grellet-Tinner and Peter Makovicky described an egg preserved alongside a Deinonychus skeleton collected decades earlier, and studies of its eggshell suggested that dromaeosaurids may have brooded their eggs in a bird-like way. Analyses of bone tissue have also been used to estimate how quickly the animal grew and how old individuals were when they died.

Ostrom’s specimens remain at the Yale Peabody Museum in New Haven, and casts of Deinonychus are displayed in museums around the world. The species has become one of the most familiar predatory dinosaurs, standing for the moment when palaeontology rethought what dinosaurs were.

Timeline

• 1931: Barnum Brown collects undescribed fragments of the animal in Montana.
• 1964, August: John Ostrom and Grant Meyer find Deinonychus bones near Bridger, Montana.
• 1964–1965: More than a thousand bones are excavated at the site.
• 1969: Ostrom names Deinonychus antirrhopus and publishes his monograph.
• 1970: Ostrom identifies the Haarlem specimen of Archaeopteryx.
• 1973: Ostrom’s paper “The ancestry of birds” appears in Nature.
• 1975: Robert Bakker’s article “Dinosaur Renaissance” is published in Scientific American.
• 1996: The discovery of Sinosauropteryx confirms that some theropods had feather-like coverings.

Why it matters

Deinonychus changed how scientists and the public imagined dinosaurs. A single Montana quarry helped turn them from slow reptiles into active, bird-like animals, and set palaeontology on the path that led to today’s consensus that birds are living dinosaurs.