A giant, stocky and extinct family of kangaroos were once able to walk on two feet, "convincing" new research has proposed.
The family of "sthenurine" kangaroos, which died out 30,000 years ago, ranged from 1 to 2 metes tall, and it's likely the largest, 250kg members of the family were too big to hop.
The study, published in the academic journal Plos One, compared today's kangaroos to the bones of their extinct cousins also finding that sthenurine kangaroos were once extremely stocky, had short snouts and used specialised arms to reach for food in trees.
The idea that the kangaroos may have walked occurred to the study's lead author Professor Christine Janis while she examined their bones in a Sydney museum.
"I thought: Wait a minute, this doesn't look right. These things were weird," says Professor Janis, a palaeontologist at Brown University in the United States.
After examining hundreds of kangaroo bones in Australian museums Professor Janis found that the extinct marsupials did appear to be moving in a very different way to their present-day cousins.
"The biggest ones got to a size that does strain the credulity of hopping," Professor Janis says - although she emphasises it is difficult to prove her claims.
"Obviously you're going out on a limb when you're proposing something about an extinct animal. But all the data fit."
Dr Vera Weisbecker, an evolutionary biologist at the University of Queensland in Australia, says she finds the study very convincing.
"The idea has been around that sthenurines may have just been too large to hop, particularly those really large forms," she told the BBC.
"It's a very unusual thing to propose. And they're making a very good case."