Diprotodontids were large herbivorous marsupials distantly related to modern wombats and koalas, with some species reaching body sizes comparable to rhinos.

Ambulator keanei here was a mid-sized example, closer to bear-sized at around 1m tall at the shoulder (~3’3″). It lived in South Australia during the Pliocene, about 3.9-3.6 million years ago, at a time when the climate was becoming drier and the local habitat was shifting towards open grasslands – and so it was was one of the first diprotodontids known to have specialized its limb anatomy for more efficient long-distance walking.

A bone in its wrist was modified into a heel-like structure, and skin impressions show large cushioning fleshy pads on the undersides of its feet. Its feet were also rotated to bear weight mainly on the outside edges, similar to the condition seen in some ground sloths, and its fingers and toes appear to have been held raised up off the ground while walking.

Balbaroo fangaroo

An early relative of kangaroos, Balbaroo fangaroo. Known from a couple of partial skulls discovered at the Riversleigh World Heritage Area in Queensland, Australia, it lived during the Early Miocene (~23-16 mya) and was probably about the size of a cat, around 45-60cm long (18-24″) not including the tail.

It had unusually enlarged canine teeth forming prominent “fangs” – hence its species name – which may have been used for display and fighting in a similar manner to some ungulates such as water deer and camelids.

Based on the skeletons of other closely related species, it probably wasn’t able to hop. Instead it would have moved around quadrupedally, and the shape of its feet suggest it was also capable of climbing like a modern tree kangaroo.