Kangaroos Have a Fifth Leg?

Kangaroos are known for being some of the best hoppers in the animal kingdom, and that's just on two legs. But when they are grazing for food on all fours, their tail becomes their most powerful asset, acting practically like a fifth leg, says a new study.

"We found that when a kangaroo is walking, it uses its tail just like a leg," Associate Professor Maxwell Donelan of Simon Fraser University, involved in the study, said in a press release. "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."

Kangaroos are known for using their tail to balance when they're hopping, but they are the only animals that use their tails like a leg.

Researchers at the University of Colorado Boulder, Simon Fraser University in Canada and the University of New South Wales in Australia looked at red kangaroos, the largest of the kangaroo species in Australia. They were surprised to find that when these animals graze on grasses, they move both hind feet forward "pair limbed" style while using their front legs and tail to balance. And though it looks awkward, it's actually very efficient.

"We went into this thinking the tail was primarily used like a strut, a balancing pole, or a one-legged milking stool," commented co-author Rodger Kram. "What we didn't expect to find was how much power the tails of the kangaroos were producing. It was pretty darn surprising."

During the study, published in the journal Biology Letters, researchers had a small group of kangaroos hop and walk on a large motorized treadmill to figure out how much energy they use at varying speeds. The results eventually showed that a kangaroo can increase its metabolism by 50 times during exercise because of its powerful tail - which has more than 20 vertebrae.

"Kangaroos are really special mammals," added co-author Terence Dawson of the University of South Whales.