There are 65 kangaroo species – ranging from the small tree-kangaroo to the red giant kangaroo, which is the largest of all. When it stands upright, it is as tall as an adult human. These marsupials have a kind of rubber band in their hind legs. It propels them upwards with each jump. The faster a kangaroo bounces, the farther the animal is “catapulted” forwards, and the less energy it consumes.