What's remarkable about this, suggests Donelan, is that the tail is anatomically quite different, being made up of more than 20 vertebrae taking on the roles of our feet, calves and thigh bones. "Animals have discovered many uses for their tails," he says, "but as far as we know, this is the first use of one as a leg."
Beyond better understanding kangaroos' movements, the research shows how important it is to push-off and help to redirect the body's velocity when transitioning from one stance limb to the next, Donelan adds. "We know healthy humans do this nearly perfectly. We know that people with gait disorders and disabilities don't do it as well, which increases the effort required for them to walk.
"Based on our original human research, fellow scientists and engineers have have built prosthetics and exoskeletons that help improve ability and make walking easier. And now we know that it is important enough that kangaroos have harnessed a limb originally evolved for swinging from trees to serve this role as functional fifth leg."
Unusual gaits by unusual animals, such as pentapedal walking by kangaroos, provide insight into the breadth of solutions available to the same biomechanical problem, notes Donelan, who has also studied the movement of shrews, cats, crocodiles, giraffes and elephants.
And what's not to find intriguing about kangaroos? "Their hopping is incredibly fast, powerful and efficient. Their walking, on the other hand, is as awkward as their hopping is graceful, but underlying the walking is this entirely new use for a tail. Biomechanically, it is all fascinating."
|Contact: Max Donelan|
Simon Fraser University