Gigantic kangaroos that used to inhabit Australia resembled enormous rabbits and walked on two legs similar to humans rather than hopping, a new study says.



Scientists have theorised that the bone structure and sheer size of the now-extinct sthenurine kangaroos, which grew to more than two metres, makes it likely the animals were unable to hop, instead walking in a bipedal motion on two hind legs.



Up to 30 species of sthenurine kangaroos roamed Australia after diverging from modern-day kangaroos about 15 million years ago. The largest of these kangaroos, Procoptodon goliah, weighed about 240kg, nearly three times the size of the largest living kangaroo.



It’s believed these kangaroos had short faces and used their arms to reach into bushes for food, unlike the ground-grazing grey and red kangaroos of today.



The combination of a two-legged walking kangaroo with a more rounded head and long ears would have made the animal resemble a freakishly large rabbit with an uncommon gait.



While the existence of these extinct kangaroo relatives was already known – along with the ancient giant wombat and marsupial lion – the belief that the animal hopped like other kangaroos was not challenged until Brown University academic Christine Janis studied the bone structure of the species.

Janis, who spent nine years studying various specimens for the research, discovered that sthenurine kangaroos had larger hips, knees and buttocks than modern kangaroos, as well as a more rigid, upright spine.

Further analysis found that the animals had stabilised ankle joints. This suggested to Janis that the giant kangaroos’ anatomy made them unable to hop, instead placing weight on one foot after another to walk. Smaller species of sthenurine kangaroos may have used their tails in addition to the two legs.

“The physiology of them is very counterintuitive to them hopping,” Janis, a professor of ecology and evolutionary biology, told Guardian Australia. Her research has been published in PLOS One.

“When I first saw a specimen at the Australian Museum, it appeared to have an arthritic back and you very rarely see that in wild animals. I thought: ‘How could it have that when it was hopping?’ That made me think these guys are not like modern kangaroos at all.

“They would have walked with a slow gait, one leg at a time. The smaller ones would have hopped sometimes, but my informed guess is that the larger ones walked all the time.

“Facially, they would have looked like a beefed-up rabbit, walking on tiptoe. If you think of how kangaroos stand when they box, that’s how they may have walked about.”

The fossil record of these giant kangaroos ends about 30,000 years ago, suggesting they became extinct, along with several other large mammals, in the Pleistocene period. Their kangaroo cousins, including larger kangaroos and rat kangaroos such as potoroos and bettongs, continued to the present.

“It may have been bad genes or bad luck, but whatever the reason, the giant kangaroos had nowhere to disperse in Australia and died out,” Janis said.

“It would be interesting to see one but I don’t particularly think I’d want to meet it. It could be quite scary. Somehow, I don’t think they were very cuddly.”

