Kangaroos are the only known animals to use their tail like a fifth leg.

Photo: flickr/thethrillstheyyieldKangaroos are well known for using their massive hind legs to hop at high speeds, with their tails held high for balance. But here's something you probably never thought about: how do kangaroos get around when they're not in such a hurry? It's not easy to hop slowly, but neither is walking with two giant hind legs and two short arms. Enter these scientists, who use video analysis and force measurements on slowly-moving kangaroos to figure out how they do it. It turns out that the 'roos actually use their tails as a fifth leg when walking. In fact, the tail provides "as much propulsive force as the front and hind legs combined." This unique use of the tail has not previously been seen in other animals. Wallaby damned!The kangaroo's tail propels and powers pentapedal locomotion "When moving slowly, kangaroos plant their tail on the ground in sequence with ...