Thursday, January 28

Koalas aren’t primates, but they move like monkeys in trees

Koalas could be Australia’s
take on monkeys and apes.

Pudgy, big-eared koalas are
celebrity marsupials, nurturing teensy young in pouches as a kangaroo does. In
koalas’ home trees, however, “we found they’re actually not moving like other
marsupials,” says Christofer Clemente of University of the Sunshine Coast in
Sippy Downs, Australia. “They’re moving more like primates.”

Australia doesn’t have trees
full of primates. So koalas independently evolved a similar gait in treetops.
Both tree-hugging lineages often navigate trunks and branches by coupling limbs diagonally —
for instance moving the right hand and left foot forward while gripping with
the other pair. As with many primates, this movement stabilizes koalas as they
step, Clemente, an evolutionary biomechanist, and his colleagues report December
17 in the Journal of Experimental Biology.

Doing that requires a good
grip, and koalas have double thumbs on their hands: two short digits separated by
a gap from three longer ones. Hind limbs also have a thumblike appendage.

When koalas reluctantly
descend to the ground, their top speed — about 10 kilometers per hour — comes in a common marsupial bounding motion with the
hind legs landing together. Bounding across ground can be about four times
faster than moving around in trees, but still leaves koalas vulnerable to
predators, particularly dogs now common in Australia. In fact, this study of
six captive animals grew out of worries
about declining koala populations forced to traverse perilous ground as increasingly fierce
fires destroy trees (SN: 7/2/18).

Koalas may be marsupials but they climb similarly to primates, new research shows. Here, a captive koala navigates an inclined log, moving diagonally opposite limbs together — such as the right front and left rear — in a primatelike gait. It uses two thumblike digits on its hands and one on its feet to grasp trunks and branches.