Kangaroos didn’t always hop, scientists say

Prehistoric kangaroos may have walked on two legs instead of hopping, a new study suggests.

It’s hard to imagine a kangaroo that doesn’t jump using the elastic energy in its powerful back legs.

But researchers say some extinct giant kangaroos, distantly related to those still alive, probably walked more like humans, striding on two legs and using one leg at a time.

Others probably walked duller on four legs, like most other mammals.

The conclusion comes from a scientific assessment of kangaroo fossils, and those of their relatives such as wallabies, spanning 25 million years, alongside new analysis of bones from the limbs and ankles of these creatures.

Professor Christine Janis, who led the review from the University of Bristol, said: ‘In the UK, where nothing bigger than a hare hops across the countryside, we’re fascinated by kangaroos and they’re in all the children’s books alongside the elephants and giraffes .

“They just seem so strange, and we assume that a hopping kangaroo is at the peak of its evolution.”

‘But in fact the survival of big hopping kangaroos these days is probably just dumb luck, which just happened because the climate changed and they had a huge amount of grassland to traverse.

“In fact, large kangaroos that jump are the exception in kangaroo evolution.”

The researchers looked at sthenurines – a relative of today’s kangaroo that can weigh up to 230 kg.

Experts believe that the point at which kangaroos can no longer jump because shifting their body weight puts too much strain on the Achilles tendon is around 160 kg, with the optimal size around 50 kg, which is about the size of most red and gray kangaroos. .

Sthenurines, first described in the late 1800s by naturalist Richard Owen at the British Museum of Natural History, are now believed to have walked on two legs, based on fossil evidence from about two million years ago, during the Pleistocene.

Illustration showing the difference in the heel bone – the strong bone that forms the back of the foot – between the modern hopper (left) and the extinct strider

Modern kangaroos, when not jumping, walk on all fours, using their tail as a fifth limb to provide extra strength.

But the sthenurines lacked the flexible spine to crouch enough to jump, and had relatively large hip and knee joints, like humans, suggesting they used one leg at a time.

The new reported analysis also shows that they had smaller heel bones than modern kangaroos, which would be less able to counter the force of the ankle movements involved in jumping around as kangaroos do today.

A second type of extinct kangaroo relative the researchers looked at — the group called the protemnodons, and nicknamed “giant wallabies” — is believed to have walked habitually on four legs, in part because of their long necks, which would have made their heads round too much. bounce. , giving them whiplash when they jumped.

These animals also had large, robust arms and shoulder and elbow joints with more limited range of motion, which would be better for weight-bearing, suggesting they were used to walking.

Protemnodons’ short feet wouldn’t provide the boost needed to start jumping.

The earliest kangaroos may have jumped, but probably not nearly as fast or far as modern kangaroos.

It’s unclear why hopping was originally adopted by these animals, but the kind of long-distance “endurance hopping” seen today is said to have evolved when the Australian climate became arid and kangaroos had to travel farther efficiently to find food.

It’s probably the only way for kangaroos to get around since the end of the Pleistocene.

The review was published in Alcheringa: an Australasian Journal of Paleontology.