Deinonychus was far from being one of the largest dinosaurs, but it was one of the most skillful hunters – one of the thugs of the dinosaur world. It always walked on its back legs and was armed with sharp claws and teeth that could rip into prey with alarming ease.
Known from more than nine skeletons, this is the animal over which the debate about whether dinosaurs were warm- or cold-blooded began. One remarkable deposit has several Deinonychus skeletons scattered around the remains of an ornithopod, Tenontosaurus, indicating that it was a pack hunter. It was the prototype for the ‘raptors’ in Jurassic Park, although modern representations have them covered in feathers.
Name: Deinonychus, meaning ‘terrible claw’
Size: 3-4m long and 1m high
Food: meat, especially the flesh of herbivorous dinosaurs
Lived: around 115 million years ago in the Cretaceous Period in North America
Until 1964, experts thought there were two separate types of theropod – big and heavy like Tyrannosaurus or small and slim like Velociraptor. Then in southern Montana, USA, fossils of a theropod were found that made the experts think again.
The fossils they found were of an animal that had features of both types of theropod. Like all bipeds, it always walked on its back legs. It was small and fleet-footed with very special weapons – two huge, wickedly curved and pointed claws. Deinonychus carried these awesome weapons on the second toe of each foot. They were as long as carving knives and just as sharp. The other toes had much smaller claws.
When Deinonychus was running, either chasing its prey or escaping from a larger predator, it used the strong muscles in its feet to pull its special, massive, hooked claws up, away from the ground. This protected them from damage. Its other claws were smaller and blunter and were used for gripping the ground and balance.
Deinonychus was built for speed. It had a slim body supported by strong, slender legs. Its very strong ankle joints could absorb enormous amounts of pressure when it ran flat out. Deinonychus’ skull had holes in the bone and scientists think that its head was quite light. A solid bone skull would have been very heavy. They believe it could run at 40km/h when it had to – faster than a human Olympic sprinter.
Deinonychus hunted in packs, just like the wild dogs that hunt prey on the African plains do today. It probably prowled around herds of Tenontosaurus and other giant herbivores. It kept a watchful eye out for young or infirm members of the herd that strayed close to where it was waiting. Then Deinonychus attacked. It used one claw to cling on to the victim, and ripped into its soft underside with the other. Next, Deinonychus’ teeth went into action. They were sharp and curved backwards, making it impossible for the victim to wrench itself free.
The tail of Deinonychus was held stiff and straight by means of bony rods. Each vertebra had bony tendons growing from it that clasped several of the vertebrae behind, solidifying the whole structure into an inflexible pole with only limited movement at the base for balance. When the tail was held outstretched, it helped Deinonychus to balance itself as it sprinted across the land. It may also have used its tail as a sort of rudder, to help it zigzag through the rocky landscape at top speed.
When experts studied Deinonychus’ skull, they found it had large eye sockets. This made them think that the animal had eagle-sharp eyesight – perfect for spotting a likely victim some distance away.
Deinonychus’ kick was so strong that it could break its own toe. We know this because a fossil bone has been found that had been fractured and then healed. Scientists have suggested that the dinosaur may have crippled itself as it kicked out at its prey.
Its brainpower was enough to keep the animal balanced while it slashed away with the killer claw on the second toe. The long, heavily clawed hands are angled so that the palms face inwards, enabling it to clutch firmly at its prey.