Study: Kangaroos Evolved to Use Tail as Extra Leg [Video]
When it's not hopping around, one of most recognized -- and popular -- animals from Down Under uses the tail it has tucked under its back legs to move forward and remain stable.
The discovery by an international team of researchers that a kangaroo relies on its tail as a fifth power leg has stunned many in the scientific community who believed the long-held notion the marsupial's tail "was primarily used like a strut, a balancing pole, or a one-legged milking stool," Rodger Kram, an associate professor at the university's department of integrative physiology and a co-author of the work, said in a news release. "What we didn't expect to find was how much power the tails of the kangaroos were producing. It was pretty darn surprising."
The findings leading to new realizations were published online in the journal Biology Letters and involved researchers from the University of Colorado at Boulder, Simon Fraser University in Burnaby, Canada, and the University of New South Wales in Sydney, Australia.
The study provides a fresh perspective on the task of foraging for food by red kangaroos, the largest kangaroo species in Australia.
When grazing on grass, the red kangaroos, it was discovered, move their two back feet forward together, in the fashion of paired limbs style while using their tails and front limbs together to support their bodies.
While the motion might appear awkward, the tails actually provide as much propulsive force as their front and hind legs combined as the animals eat their way over the landscape."They appear to be ... ungainly walkers when one watches them moseying around in their mobs looking for something to eat," said Kram. "But it turns out it is not really that awkward, just weird."
In human locomotion, the back foot acts as the accelerator while the front foot acts as a brake, which is not particularly efficient, said Kram.
In that way, a walking kangaroo is more like a skateboarder who has one foot on the board and uses the other to push backward off the pavement, increasing the forward motion.
The researchers assert no other known animal uses its tail like a leg.
The research project originated in 1973, when Emeritus Professor Terence Dawson of Australia's University of New South Wales, a visiting professor at Harvard University at the time, coaxed a small group of kangaroos to hop and walk on a large motorized treadmill, in order to measure the energy costs of locomotion at varying speeds.
Later for the study, researchers videotaped five red kangaroos in Dawson's Sydney lab that had been trained to walk forward on a force-measuring platform with Plexiglas sides and sensors for measuring vertical, backward and forward forces from the legs and tails of the animals.
"I'm envious of kangaroos," said Kram, also a competitive runner. "When they hop faster, they don't use energy at a faster rate. They have the ability to move faster and not get tired, the ultimate goal of a runner."
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