By Natalie Warburton @aNATomy_lab. Studying animal behaviour and ecology can involve hundreds of hours of field work in uncomfortable conditions, and for Australian mammals at least, very long nights. But what about animals from the past? How can we understand their behaviour and ecology, and what can this tell us about how ecosystems and the environment have changed over time?

A new paper out this week demonstrates the painstaking process of gleaning stories from ancient bones to reveal unexpected and astonishing animals…

Imagine if you will, walking through the scrub of the Nullarbor Plain… it’s pretty hot, it’s dry, and there are very few shady trees as the name suggests. But now imagine finding an animal with the legs and face of a kangaroo, with huge muscly arms and a longer than usual neck up a non-existent tree… this was what working on these fossils was like!

These extinct wallabies belong to the genus Congruus. This name was based on previously described skulls and teeth that suggested they were pretty similar to other closely related wallaby species: long faces, teeth well-suited to a herbivorous browsing diet. “Congruent” one might say with what we might expect it to look like based on its near relatives.

However, (VERY) close inspection of every bone of the almost complete skeletons from the Thylacoleo Caves revealed features that were entirely INcongruent with your run-of-the-mill wallaby.

Rather than being somewhat diminutive, with a gracile body and reduced forelimbs, this animal had big hands, long fingers with massive, curved claws, and arms with huge muscles for grasping and holding on. “Ok” I hear you say. “Maybe they were just really into wrestling… I mean, I’ve seen big roos fighting and you’ve told us about that before.” (But these are even bigger arm muscles!)

The proportions of the feet are not like a typical 50kg kangaroo. They are broader and relatively shorter in the ankle and foot bones, more like the foot proportions of a forest wallaby or even a quokka. But the toes are too long and like the fingers they have long, downward curved claws… not very good for efficient hopping across the open plains one might think.

But wait, there’s more! The vertebrae are generally smaller and more flexible than you would expect, and though the proportions are consistent, there is one more thoracic vertebra than normal. Perhaps most interestingly is that the neck is notably longer than in other roo relatives.

“What’s all this got to do with climbing trees?” you ask.

Well, if you are a pretty big animal up a tree, moving around to reach leaves can be pretty tricky. Having a longer, more flexible neck than usual might be pretty useful. Sloths, for instance, have unusually long necks (and are one of the only mammals to have more than 7 cervical vertebrae). So maybe there is something in this longer neck business…

But why is this totally incongruent wallaby important?

Well, it tells us something about the environment at the time. Roughly 45-75 thousand years ago (not really very long, geologically speaking), there were tree-climbing wallabies on the Nullarbor. And these weren’t the only ones; we’ve already described two new species of extinct tree-kangaroos (Bohra spp.) from the same fossil deposits. So where are the trees now, or even any evidence of trees, and what sort of trees were they?

Unfortunately, at this stage, we don’t know! But what we do know is that previous interpretations of the changing environment for this area don’t really match with the stories that are written in the bones of the animals that lived there.

Like all good science, we are left with more questions than we started with …  but isn’t that what makes science fun?!

Find out more:

Daily Mail An extinct tree-climbing kangaroo in a ‘treeless plain’ | Daily Mail Online

International Business Times An Extinct Tree-climbing Kangaroo In A ‘Treeless Plain’ (ibtimes.com.au)

Pedestrian TV Australia Was Once Home To Swole Kangaroos Who Could Climb Trees & We Say: Bring Them Back (pedestrian.tv)

Science Media Exchange Researchers discover new climbing kangaroo species – Scimex

Cosmos Magazine Ancient tree-climbing kangaroo discovered – Cosmos Magazine

Australian Geographic Ancient species of tree kangaroo discovered – Australian Geographic

RTL today RTL Today – Roos in trees: An extinct tree-climbing kangaroo in a ‘treeless plain’

News Beezer (Singapore) Researchers discover extinct species of climbing kangaroo (newsbeezer.com)

New scientist Large extinct Australian kangaroo spent half its life in trees | New Scientist

Belga image Belga Image

6PR interview: MediaView (tveyes.com)

References

Congruus kitcheneri…  (if you like bones you’ll LOVE the pictures!)

Warburton, N.M. and Prideaux, G.J., 2021 The skeleton of Congruus kitcheneri, a semiarboreal kangaroo from the Pleistocene of southern Australia Read more

Amazing fossils from Thylacoleo Caves discovered in 2002, and what was known of the environment at the time

Prideaux, G.J., Long, J.A., Ayliffe, L.K., Hellstrom, J.C., Pillams, B., Boles, W.E., Hutchinson, M.N., Roberts, R.G., Cupper, M.L., Arnold, L.J., Devine, P.D., and Warburton, N.M. (2007) An arid-adapted middle Pleistocene vertebrate fauna from south-central Australia. Nature 445, 422-425. Read more

Relationships between kangaroos and wallabies

Prideaux, G.J., and Warburton, N.M. (2010) An osteology-based appraisal of the phylogeny and evolution of kangaroos and wallabies (Macropodidae: Marsupialia). Zoological Journal of the Linnean Society 159, 954-987. Read more

Illuminating fossil tree-kangaroo from the Pleistocene of WA

Prideaux, G.J., and Warburton, N.M. (2008) A new Pleistocene tree-kangaroo (Diprotodontia: Macropodidae) from the Nullarbor Plain of South-Central Australia. Journal of Vertebrate Paleontology 28, 463-478. Read more

More fossil tree-roos from the Nullarbor Plain

Prideaux, G.J., and Warburton, N.M. (2009) Bohra nullarbora sp. nov., a second tree-kangaroo (Marsupialia: Macropodidae) from the Pleistocene of the Nullarbor Plain, Western Australia. Records of the Western Australian Museum 25, 165-179. Read more

 Ankle bones of kangaroos from different environments

Warburton, N.M., and Prideaux, G.J. (2010) Functional pedal morphology of the extinct tree-kangaroo Bohra (Diprotodontia: Macropodidae). In ‘Macropods: The Biology of Kangaroos, Wallabies and Rat-kangaroos.’ (Eds. G Coulson and MDB Eldridge) pp. 137-151. (CSIRO Publishing)

Sexual dimorphism in arm muscles for fighting

Warburton, N.M., Bateman, P.W., and Fleming, P.A. (2013) Sexual selection on forelimb muscles of western grey kangaroos (Skippy was clearly a female). Biological Journal of the Linnean Society 109, 923-931. Read more