Kangaroos that roamed Australia 100,000 years ago didn't hop like the kangaroos you see today, according to a new study. How the extinct "sthenurines" got around, scientists weren't quite sure until now.

The study, published online in the journal PLoS ONE on October 15, 2014, suggests that the extinct roos had a slow yet steady walk.

"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," said Dr. Christine Janis, a professor of ecology and evolutionary biology at Brown University and the lead author of a new study about the ancient kangaroos, told The Guardian. "I thought: 'How could it have that when it was hopping?' That made me think these guys are not like modern kangaroos at all."

Researchers analyzed more than 140 kinds of modern and extinct kangaroo and wallaby skeletons, including sthenurines, for their study.

The sthenurines' anatomy suggests that the animals, which likely weighed as much as 530 pounds, would have been bad hoppers. Instead, they most likely shifted their weight from one leg to another as the moved, instead of moving both legs to hop, according to the study.

Previous studies have dismissed the idea that ancient kangaroos got around by walking on all fours, using its tail as well as its four limbs. Scientists call this pentapedal locomotion.

"If it is not possible in terms of biomechanics to hop at very slow speeds, particularly if you are a big animal, and you cannot easily do pentapedal locomotion, then what do you have left?" Janis said in a written statement. "You've got to move somehow."

Kangaroo movement remains a controversial topic among paleontologists despite the discovery.

"I suspect that the locomotion of sthenurines will continue to be debated," Dr. Natalie Warburton, a senior lecturer of anatomy at Murdoch University in Australia, who was not involved in the new study, told Live Science. "But that is what science is about, proposing hypotheses based on the available evidence and then testing them."

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