Red kangaroos, the largest of the kangaroo species in Australia, don't just use their tails to jump high and fast. When they're grazing for food, in fact, their tails are able to generate enough force that they propel the kangaroo rather like a fifth leg—a trait scientists say they've never seen before in the animal kingdom, reports National Geographic. "Their tails have more than 20 vertebrae, taking on the role of our foot, calf, and thigh bones," says one scientist.
The so-called "fifth leg" also allows for greater efficiency than the human gait, where the leg that's behind powers forward while the front leg brakes. One of the researchers compares the kangaroo's gait to that of a skateboarder whose free foot (here a tail) pushes off the pavement to propel it forward. "It's a real wonder of nature, how these kangaroos move about and what they are able to do," he tells Phys.org. The tail is so strong that males have been observed, mid-fight, supporting their entire bodies with their tails so they can lift their hind legs to kick. (Click to read about a 94-year-old woman who fought off a red kangaroo with a broom.)