Grazing Red Kangaroos Use Their Tail As An Extra Leg
July 2, 2014

Grazing Red Kangaroos Use Their Tail As An Extra Leg

Gerard LeBlond for - Your Universe Online

According to a new multi-institutional study of red kangaroos, it has been found that when grazing on all fours, these marsupials use their tail as an extra leg. While grazing, the tail helps with movement by pushing the kangaroo forward as it walks.

The study, published online in Biology Letters, was co-authored by Associate Professor Maxwell Donelan from the Simon Fraser University, and Associate Professor Rodger Kram from CU-Boulder's Department of Integrative Physiology along with Postdoctoral Fellow Shawn O'Connor of Simon Fraser and Emeritus Professor Terence Dawson of the University of New South Wales.

“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,” said Donelan.

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

The red kangaroo is the largest species of kangaroo in Australia. The team found that when they graze, they put their hind feet forward and use their front legs and tail for support.

“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,” Kram said.

Humans use their feet for movement by pushing off with the back foot and breaking with front foot. In comparison, according to Kram, when the kangaroo moves forward, it is like a skateboarder with one foot on the board and one on the ground -- the tail helps propel the kangaroo in a forward motion. According to the team, the kangaroo is the only animal that uses its tail as a leg.

“Their tails have more than 20 vertebrae, taking on the role of our foot, calf, and thigh bones,” added Donelan.

Research on the subject began in 1973 when Dawson taught a small group of kangaroos to hop and walk on a motorized treadmill to measure the energy used at different speeds. The results demonstrated that the kangaroo’s metabolism increased by 50 times during the exercise.

“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,” Dawson said.

The male kangaroos will also use their tail to boost balance when trying to gain dominance by grabbing each other on the chest and kicking each other in the stomach. This action is for the purpose of gaining a mate for reproduction.

The study consisted of the researchers videotaping five red kangaroos in Dawson’s Sydney lab that were trained to walk forward using a platform with Plexiglas sides. The kangaroos were rewarded treats for walking forward, according to Kram. Sensors were attached to monitor vertical, backward and forward force from the legs and tails of the kangaroos.

Most of the research data was collected years ago, but other team members were encouraged to release the information. “This was a study we just could not let go of. It was just too much fun. It's a real wonder of nature, how these kangaroos move about and what they are able to do,” Kram said.

The ancestors of the kangaroo were opossum-like and lived in trees, they eventually evolved to the ground. Kram compared it to a roll of duct tape, “you know you are going to use it, you just don't know when,” he said. “I'm envious of kangaroos. When they hop faster, they don't use energy at a faster rate. The have the ability to move faster and not get tired, the ultimate goal of a runner,” he said, being a competitive runner himself.

Kram and his students have also studied the movements of other creatures, from elephants, tortoises, and llamas, to ostriches, beetles and many others in between.


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