Kangaroos aren’t like other animals.
They’re marsupials, of course, meaning they give birth to practically embryonic live young but carry them around in pouches until they are ready to face the world. They live only in Australia, where they are one of the few native animals to have thrived since European settlement. And they hop.
No other animal of comparable size moves this way. As Swedish carmaker Volvo admitted recently, the hopping of the large marsupials completely baffles the systems that power their self-driving cars. Kangaroos’ locomotion has posed plenty of questions for scientists over the years, too.
Why do kangaroos hop? According the Terence J Dawson, the Australian scientist who literally wrote the book on kangaroos, at speeds above 12 kilometres per hour or so, hopping is more efficient than running. The efficiency increases with speed, so that at 40 kilometres per hour, according to Dawson, a kangaroo is only using half as much energy as a quadruped would.
At low speeds, however, hopping isn’t very efficient at all. But instead of reverting to four legs for low-speed manoeuvres, kangaroos in fact use their tails as a “fifth leg” in a unique pentapedal walking style.
The straight, high-standing posture in the photo above might look inquisitive, but it’s more likely a first threat or warning not to approach.