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New theory on one of Australia's strangest prehistoric marsupials

Timothy McDonald reported this story on Thursday, November 22, 2012 12:50:00

ELEANOR HALL: Is it a wombat, a giant koala or something else entirely?

A team of palaeontologists has a new interpretation of one of the most curious animals to be found in the fossil-rich Riversleigh region in north-west Queensland.

When the Nimbadon fossil was first discovered, it was thought to be a ground dweller with a body form similar to a sheep.

Now, Professor Mike Archer and his colleague Dr Karen Black from the University of New South Wales have published research suggesting it might have looked very different.

Professor Archer spoke to Timothy McDonald.

MIKE ARCHER: We thought it was kind of like a sheep-like marsupial, maybe somewhere like a cross between a wombat and a sheep and we just assumed that it was running around on the forest floor of these ancient rainforests that covered this region.

But then Karen started looking at the feet and we've all been sort of puzzled about what she's been finding. It's not at all what we expected. They have gigantic claws, narrow almost vicious eagle-like claws that don't make any sense for an animal that is running around of the forest floor and the only animal today that has claws remotely like this, only much smaller, is the koala and the koala of course is almost strictly arboreal, lives in the trees so suddenly this is a different kind of an animal than we expected.

It is an arboreal animal probably hanging upside down, moving in herds through the forest canopy.

TIMOTHY MCDONALD: This creature that you found though is much, much bigger than a koala?

MIKE ARCHER: Yeah, this creature is probably not much smaller than one of us actually. It is a big heavy animal, they were carrying young, we found tiny little pouch young in this fossil deposit. So whole families were moving through these trees and occasionally, you know, someone would sneeze and drop out of the tree and end up in the cave.

So we are trying to figure out what was this animal like, what did it do ecologically, what was its role in these forests because we don't have anything like this today in any of Australia's forest. Yes, there are things like tree kangaroos but they are much smaller and they're not shaped like this. They don't have these powerful claws and powerful forelimbs for hiking up trees in the same way that this animal must have done.

TIMOTHY MCDONALD: So do you suspect then that perhaps it is one of these evolutionary cul-de-sacs, one of these evolutionary dead-ends that occupies a niche and then kind of fades from existence?

MIKE ARCHER: An evolutionary dead-end, somebody might think of this thing that way, but on the other hand you know, we've only been around for 300,000 years. This thing was around for several million so I think it was doing quite well. The thing that undermined the future of this extraordinary group of animals appears to have been climate.

The climate whacked these ancient rainforests, started to dry them out and they began to open up and a lot of these very specialised weird things that were so characteristic of Australia basically lost out in the climate change game. It is a bit of a warning for us today.

TIMOTHY MCDONALD: Do we have any sense of what it is closest relatives might be?

MIKE ARCHER: If you have to pick a modern animal that they are most closely related to, and yet they would have looked quite different than this, it would be the wombat but the wombat is kind of like a fat, tubby version of these things. These were slender, powerfully-built animals, more like on a sheep-like ground plan but with massive forelimbs, big muscles in the arms for holding the weight of these large animals, climbing them up the tree and then holding on with these powerful forelimbs, a bit like sun bears do.

So yes, probably a bit while related to wombats but really not looking very much like a wombat at all.

TIMOTHY MCDONALD: Do we have any sense of whether it was carnivorous or herbivorous animal?

MIKE ARCHER: We are getting very cautious about interpreting diets these days but if we look at the shape of their teeth you would have to say it was probably a plant eater but then there are other animals that if you casually look at their teeth you might say the same thing about but as we study them more closely we find that they are omnivorous and sometimes even carnivorous.

So I think first guess is it is a leaf eater, you know, it's not eating any plants on the ground, it's eating whatever the trees were producing up above, maybe even fruit as well as leaves but maybe if the odd snake didn't move out of the way fast enough, it might have gone down the gullet of these things as well.

ELEANOR HALL: Extraordinary creatures. Professor Mike Archer from the University of New South Wales speaking to Timothy McDonald.



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  • Nimbadon
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