Large extinct Australian kangaroo spent half its life in trees

A large, extinct kangaroo that lived 40,000 years ago spent half its time living in trees – a relatively unusual adaptation for a heavy marsupial.

In 2002, Natalie Warburton at Murdoch University in Perth and Gavin Prideaux at Flinders University in Adelaide, both in Australia, excavated the remains of two kangaroos, a male and female, at the Thylacoleo caves of Nullarbor Plain, in south-western Australia.

The kangaroos belong to a species that went extinct about 40,000 years ago – one of many large-bodied animals that were wiped out at the time.

This species of kangaroo was first described in 1989 but, at the time, skulls and teeth were the only fossils available for study. The remains were used to name the species: Wallabia kitcheneri.

Warburton and Prideaux excavated two nearly complete skeletons. They have now studied them to gain a better understanding of how the kangaroo lived and moved around.

“These fossils have unusually long fingers and toes with long, curved claws, in comparison to other kangaroos and wallabies,” says Warburton.

From features of the bones, the researchers could also determine that the kangaroos had powerful arm muscles to raise and hold up their body weight, and a longer, more mobile neck than other kangaroos.

“[The neck] would be useful for reaching out the head in different directions for browsing on leaves,” says Warburton.

The researchers suspect the kangaroo was semi-arboreal, meaning it spent half of its time on land and half in the trees. A handful of small-bodied kangaroo species alive today are also adapted for life in trees, but individuals of the ancient species may have weighed at least 50 kilograms, much heavier than modern tree-dwelling kangaroos.

“When climbing, [the extinct kangaroo] moved something like a cross between a koala and a very large-bodied primate, not swinging under branches though, but with a big heavy tail and head like a kangaroo,” says Warburton.

“These specimens come from an area that is now bare of trees, so it tells us that the habitat and environment were once really different to what they are now,” she says.

Because of the new findings that it was partly tree-dwelling, the two researchers have renamed the species Congruus kitcheneri because the anatomy is unlike that of any known species of Wallabia.

Tim Flannery at the University of Melbourne, who led the team that described the species in 1989, welcomes this change. “I little thought when I described the dental remains of Wallabia kitcheneri that its post-cranial skeleton would be so anomalous,” he says.