A new study published in the journal Biology Letters shows that red kangaroos use their muscular tail just like a leg.

Red kangaroos (Macropus rufus) are the largest living marsupial in the world and the largest of the kangaroo species in Australia.

When grazing on grasses, they move both hind feet forward ‘paired limb’ style while using their tails and front limbs together to support their bodies.

“They appear to be awkward and ungainly walkers when one watches them moseying around in their mobs looking for something to eat. But it turns out it is not really that awkward, just weird,” said Dr Rodger Kram of the University of Colorado Boulder, who is a co-author on the study.

“Kangaroos are really special mammals. Work over the past half century has turned the notion that they belong to an inefficient, primitive group of mammals totally on its head,” added co-author Prof Terence Dawson of the University of New South Wales.

For the study, the scientists videotaped four adult female and one juvenile male red kangaroos that had been trained to walk forward on a force-measuring platform with Plexiglas sides.

The platform’s sensors measured vertical, backward and forward forces from the legs and tails of the animals.

The kangaroos had been taught that walking forward on the platform resulted in being rewarded with sweet treats.

“We found that when a kangaroo is walking, it uses its tail just like a leg. They use it to support, propel and power their motion. In fact, they perform as much mechanical work with their tails as we do with one of our legs,” explained study senior author Dr Maxwell Donelan of Simon Fraser University.

In human locomotion, the back foot acts as the gas pedal and the front foot acts as a brake, which is not especially efficient. But a walking kangaroo is similar to a skateboarder who has one foot on the board and uses the other foot – in this case a tail – to push backward off the pavement, increasing the forward motion.

The kangaroo tail also acts as a dynamic, springy counterbalance during hopping and boosts balance when male kangaroos grab each other by the chests or shoulders, then rear back and kick each other in the stomach in an attempt to assert dominance for the purpose of reproduction.

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Shawn M. O’Connor et al. 2014. The kangaroo’s tail propels and powers pentapedal locomotion. Biol. Lett., vol. 10, no. 7; doi: 10.1098/rsbl.2014.0381