Sthenurus stirlingi strong tail giant kangaroo Macropus giganteus eastern grey kangaroo
LEFT: Artist rendition of Sthenurus walking by Brian Regal.
RIGHT: A. Sthenurus stirlingi (short-faced giant kangaroo) B. Macropus giganteus (modern eastern grey kangaroo)

You have to crawl before you can walk, unless you’re a kangaroo. Modern kangaroos hop or use all four limbs and tail for pentapedal locomotion but prehistoric kangaroos walked, according to a paper published in the journal PLOS ONE. Sthenurus stirlingi (short-faced, giant kangaroo) lived for 12.5 million years until going extinct 30,000 years ago. The giant kangaroo was 6-1/2 feet tall, 10 feet long and 550 pounds.

“I don’t think they could have gotten that large unless they were walking,” said study author Christine Janis, an evolutionary biologist at Brown University.

Sthenurus had numerous traits that suggest it walked. It had a stiffer spine ill-suited for hunching over. Its forelimbs were specialized for browsing and wouldn’t have supported its body weight, whereas its hind legs were strong enough to balance its weight over a single limb for walking.

“They had big bums, and much more room for these gluteal muscles than today’s kangaroos,” Janis told New Scientist.

Walking upright does have a downside. This form of locomotion is much slower and may contributed to their extinction. They could have found it difficult to migrate to find food when the climate changed or humans could have killed off the slow moving creatures.

Sthenurus stirlingi strong tail giant kangaroo