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...