Is There Such a Thing as a 5 Legged Animal?

The tail of a kangaroo provides more power of movement than its fore and hind limbs.
Is There Such a Thing as a 5 Legged Animal?
A kangaroo stands next to a rare waterhole as sheep gather as they look for food on a station near White Cliffs in New South Wales, Australia, on July 19, 2002. (William West/AFP via Getty Images)
Irina Antonova

Biologists would most likely say "no," but one group of scientists believes otherwise.

Australia is known for its unique flora and fauna, and kangaroos are one of its amazingly unique animals.

It is not just its looks, but its anatomy also draws the attention of animal lovers and researchers alike.

The movements of a kangaroo are one of its more unusual features and the subject of a study by scientists from Simon Fraser University in Burnaby, Canada.

They noticed that when the red kangaroo (Macropus rufus) walks it actually uses five “legs,” also known as “pentapedal” or “five-legged” movement.

The animal places its tail on the ground together with its front legs, as to form a tripod-like structure while it moves its back legs forward.

The kangaroo does this most of the time to graze on shrubs and grass.

"We found that when kangaroos are walking pentapedally—which they spend more time doing than hopping—they use their tail just like a leg," said J. Maxwell Donelan, a biomedical engineer at Simon Fraser University and main author of their paper in The Royal Society Publishing.

The Study

In their paper, the researchers explain that they worked with five red kangaroos— four adult females and one young male—walking around their lab over a special walkway.

The walkway was mounted with a force plate which recorded vertical and longitudinal forces.

Over this walkway, there was a ceiling that prevented the kangaroos from hopping, so they walked pentapedally with everything being recorded.

Scientists concluded that the unique biomechanical movements of the tail—to power the body forward—were akin to an additional leg.

"The tails provided more forward-moving force than both the animals' forelimbs and hindlimbs combined,” scientists from Canada said.
"This neat study provides, at last, definitive evidence of the use of the tail during pentapedal locomotion in large kangaroos," said marsupial anatomy expert Natalie Warburton, in the journal Science.

According to her, the kangaroo tail is "truly a fifth limb."

Daniel Schmitt, a vertebrate locomotion expert at Duke University in Durham, North Carolina, said that, "The surprising reality when it comes to kangaroos and many other species, is that we don't often known what tails are used for."
"This paper shows that tails are much more interesting than we thought,” Schmitt said.
Michael Bennett of the University of Queensland in Australia, said the findings were of no surprise, because when male kangaroos fight, their tail are strong enough to support the entire body weight of the animal, so the male can lift its entire body to kick its opponent.
"It's amazing what these kangaroos are doing," said Kristian Carlson of South Africa's University of the Witwatersrand, "What is surprising is the extent to which the tail is propelling the body forward and the amount of force it's providing."
Irina Antonova holds a M.S. in Genetics (from Bulgaria) and Ph.D. in Biotechnology (from Australia). Throughout her career, Irina worked as a scientist in academia and the industry, as well as teaching at universities. She enjoys learning about the mysteries of mind, body, life, and the universe.