Australia: The Land Where Time Began

A biography of the Australian continent 

Deinonychus antirrhopus   Dromaeosauridae

Some characteristics of Deinonychus 

• A bipedal dinosaur with long, slender legs
• The unusual feature of its feet was its 3 toes, 2 of which were used in walking with the inner toe on each foot being kept clear of the ground and possessing a very large curved claw.
• A long tail counterbalanced the front part of the body at the hip. The tail was flexible and muscled near the hips, tapering very narrow and stiffened by thin, bony rods along the rest of its length.
• It had a short, compact chest, that supported very long arms with raptorial, 3-fingered hands, each ending in a sharp claw. The hand swiveled at the wrist allowing the hand to be swung in a raking arc like those of a preying mantis.
• It had a goose-like slender curved neck with a very large head, the long jaws being lined with sharp teeth with serrated edges. The eye sockets are very large and seem to point forward and a braincase that was much larger than expected.

It is confirmed to be a predator by its jaws and teeth. The large eyes pointed forward and had a degree of stereoscopic vision enabling them to judge distance accurately. The author1 suggests this depth perception is at least partly responsible for the size of its large brain that is implied by its large braincase. Processing large amounts of complex visual information rapidly required large optic lobes to allow the animal to respond quickly and large motor areas of the brain were needed to large and elaborate  to enable the animal to process the higher brain commands and coordinate rapid muscular responses.

The light stature and slender legs suggest that it was a sprinter also suggests the need for an elaborate brain. With only 2 walking toes the resulting narrow foot was less stable than the more usual 3-toed foot for bipedal dinosaurs indicating it had a particularly well-developed balance mechanism that probably needed to be learned by feedback between the brain and the musculoskeletal system.

The large claw on both the feet is obviously an offensive weapon but there has been a number of mechanisms of use that have been proposed. The author¹ has proposed 2 possible mechanisms; according to one suggestion it was capable of slashing at its prey with 1 foot at a time in the fashion used by large flightless birds such as ostriches and cassowaries of the present. If it used this method it would indicate that it could stand on 1 foot occasionally. Another suggestion is that it could have attacked with a 2-foot kick as kangaroos males do in their fights, holding the opponent with the arms while raking at the opponent's abdomen with its claws. If it used either of these possible methods of attack the long arms with their sharp clawed hands would have been useful as grapples for holding and ripping at the prey, especially with the raking movements made possibly by their wrist joints. He also suggests the long whip-like tail may have been used as a cantilever in a manner to the pole used by tight rope walkers to aid with balance while it was slashing with 1 foot. It could also have been used as a dynamic stabiliser when chasing fast-moving prey that changed direction rapidly or when leaping onto the backs of prey.

Links

• DinoData
• Peter Schouten

Sources & Further reading

1. Norman, David, 2005, Dinosaurs: A Very Short Introduction, Oxford University Press