The giant Sthenurus, dead for 30,000 years, was three times the size of the modern-day kangaroo and probably didn’t hop at all. With a leap of the imagination, the researchers were able to visualise how the giant Sthenurus kangaroo, which weighed up to 240kg, moved around by putting one foot in front of another rather than hopping on both legs.
Bipedal hopping is a quintessential feature of kangaroo locomotion, but the Sthenurine group of extinct ‘roos was clearly made for walking, according to Christine Janis of Brown University in Providence, Rhode Island, who led the study published in the on-line journal PlosOne.
“When I first saw a mounted skeleton of a Sthenurine I was struck by how different it was in the back end to modern kangaroos, despite the superficial similarity of long hind legs,” Dr Janis said.
“My work emphasises that the large modern kangaroos are highly specialized in their anatomy for hopping in comparison with other large extinct kangaroos,” she said.
“Sthenurines almost certainly did hop, except perhaps for the very largest ones. The issue is that their anatomy is also suggestive of bipedal walking, which is the unexpected issue here,” she added.
In terms of locomotion, they were unlike today’s kangaroos, with an anatomy ill-suited for hopping. They likely walked in an upright bipedal stance – putting one foot in front of the other, just like people – in a way modern kangaroos cannot, the study found.
This was facilitated by larger hips and knee joints as well as stabilized ankle joints unlike today’s kangaroos but like animals that walk or run. They also had a relatively inflexible spine not conducive for hopping.
“Today’s kangaroos mostly use hopping as their fast gait – although tree kangaroos rarely hop. But for slow speeds they use a type of ‘pentapedal’ walk, using all four legs and the tail,” said Janis.
With their stiff backs and specialized hands, this “pentapedal” gait would have been difficult for sthenurines. They also lacked certain specialized anatomical features of modern large hopping kangaroos, the researchers said.
Janis said she suspected smaller sthenurines used bipedal walking at slow speeds and may have switched to hopping at faster speeds. “But the largest ones may have walked rather than hopped most if not all of the time,” Janis said.
Walking rather than hopping would have been a slower and less efficient means of moving fast, which may have been one of the reasons by the giant, walking kangaroo went extinct, leaving their hopping cousins to fill the void, Dr Janis explained.
Sthenurine kangaroos died out around the same time that modern humans arrived in Australia and began to spread across the continent, suggesting that their demise may have had something to do with human hunting. Virtually all kangaroos today hop, although a species called the Musky Rat-kangaroo does not.