By Sam Wong
An ancient group of kangaroo relatives called balbarids had multiple ways of getting around, including hopping, bounding and climbing. The finding may mean we have to rethink how modern day kangaroos came to hop.
Kangaroo evolution has been difficult to piece together because there are very few fossils older than one or two million years. The prevailing view of kangaroo evolution is that they began hopping when the climate in Australia became drier and wiped out many forests, but new fossil evidence suggests that their relatives were hopping much earlier.
The balbarids were distant cousins of modern kangaroos and lived in forests when the Australian climate was wetter. They went extinct around 10 to 15 million years ago when the climate dried out.
One of the most complete skeletons, from a species in the balbarid family called Nambaroo gillespieae, suggests that these animals moved on four legs and did not hop like true kangaroos.
Benjamin Kear at Uppsala University, Sweden, and colleagues have now analysed a set of more fragmentary remains, including ankle bones, a calf bone and a claw. They suggest that some balbarids galloped, some hopped, and some climbed in trees.
That’s true of modern kangaroos too, if you look beyond the most famous among them. There are rat kangaroos that scurry in the undergrowth and burrow, and tree kangaroos that live in the forests of New Guinea. Short-faced giant kangaroos, which went extinct 30,000 years ago, walked on two legs like us.
This versatility has been key to kangaroos’ success, enabling them to exploit a huge range of terrestrial environments, says Kear. The origin of hopping goes all the way back to virtually the beginning of kangaroo evolution, he says.
That means we have to rethink how and when kangaroos came to hop. “Hopping didn’t evolve with the climate; hopping was already there and took advantage of environmental change when it occurred,” says Kear.
Journal reference: Royal Society Open Science, DOI: 10.1098/rsos.181617
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