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Koalas clamber about in trees much like primates, despite being separated from them by tens of millions of years of evolution.

鈥淭hey are the closest thing we have to primates in Australia,鈥� says Christofer Clemente at the University of the Sunshine Coast in Sippy Downs, Australia.

Koalas are marsupials that carry their young in pouches. Although marsupials are mammals, their ancestors split from those of other mammals such as dogs and monkeys at some point during the era of dinosaurs.

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Isolated in Australia for millions of years, marsupials like koalas have evolved independently. There were no primates in Australia before humans arrived.

Despite koalas鈥� fame, very little was known about how they walk and climb, says Clemente. His team filmed six koalas living in Queensland Zoo, in a habitat that mimicked the eucalyptus forests where wild koalas live. The koalas were filmed both in trees and on the ground.

Marsupials often bound across land, with both hind feet hitting the ground at the same moment. But Clemente and his team found that while they were in trees, the koalas moved more like primates.

Many mammals have a gait in which the two legs on the same side of the body move together, supporting each other. 鈥淗owever, primates, and now koalas, show a slightly different gait,鈥� says Clemente. Diagonal pairs of legs move together, so the front left moves with the back right.

By itself, this isn鈥檛 unique: cats also do it, for example. But in primates and koalas, the rear leg is put down before the opposite front leg. For example, if the rear right leg touches down on the ground, the next foot to be put down will be the front left, and vice versa. This gait has been seen in only a few animals other than primates, including kinkajou and woolly opossum.

鈥淲e think this is linked to stability on narrow supports,鈥� says Clemente. Always having one leg holding a branch on each side may make koalas less likely to wobble to one side and fall off.

When they were on the ground, they still took relatively long strides, which is typical of primates. They could move four times faster on the ground than in trees, reaching around 10 kilometres per hour.

Clemente says understanding koalas鈥� gait will help us understand their vulnerability to forest clearances. For instance, 鈥渂igger spaces between trees might leave them vulnerable to predation or dog attacks,鈥� he says. The next step is to find out how the koalas use their walking styles in the wild, in order to determine which habitats suit them best.