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Remains of extinct land-dwelling crocodile found

MARK COLVIN: In north Queensland and the Northern Territory, people are used to being careful around waterways because of the danger of saltwater crocodiles. But it seems that in prehistoric times, the crocodiles' ancestors may not all have been so wedded to water.

The remains of a prehistoric crocodile recently found in Tanzania suggest that some were land dwelling creatures, which most likely behaved like modern predatory mammals. Researchers say it's likely that these crocodiles roamed Australia at some point.

Timothy McDonald reports.

TIMOTHY MCDONALD: Most people think of them as flesh eating giants with huge fangs and armoured skin. And they may be among the world's most menacing and feared predators, but they can be curious and surprising creatures as well.

Northern Territory-based taxidermist and crocodile hunter, Mick Pittman recently found an odd one, with tiny spurs protruding from the underside of its back legs.

MICK PITTMAN: I don't know whether the crocs been playing up with a platypus or not but it looks a bit funny, I reckon. I've never seen anything like it in the, like my family have been involved in this industry for 53 years, it's a pretty rare item.

TIMOTHY MCDONALD: That may be strange for a modern crocodile but some of its distant, extinct relatives appear even more unusual. One huge prehistoric croc was about the length of a bus and weighed in at around eight tonnes.

But a team of researchers working in Tanzania recently dug up something quite different and a little less intimidating. Dr Eric Roberts is a Lecturer at the School of Earth and Environmental Sciences at James Cook University.

ERIC ROBERTS: This new crocodile probably would have stood about 10 to 20 centimetres high at its shoulders and would have, for all intents and purposes, been about the size of a house cat and unlike most crocodiles that we think of today as being mostly aquatic and attack predators, ambush predators, this thing has every appearance of having been a fairly active terrestrial or land dwelling animal and it probably would have actually occupied the niches in Gondwana in the southern land masses about a 100 million years ago, that we typically think of as reserved for mammals today.

TIMOTHY MCDONALD: The way that you describe it, it doesn't really sound anything like a crocodile. How do you even know it is one?

ERIC ROBERTS: Well, the overall morphology is very much still crocodilian in terms of its shape of its bones, shape of its skull, the different number of openings in the actual skull tells us quite a lot.

However, if you didn't see that whole skeleton or didn't see the entire skull as when we first discovered this, we actually had two partial skulls to begin with and we thought we had a new mammal and that's frankly what we were going on.

And that changed when we actually recovered a full, articulated skeleton and at that point we could really say, okay this is anatomically a crocodile that has some features that are very much converging on or similar to what we think of as mammalian features, in particular in the jaw mechanics and the teeth. But there are also a little bit longer legs, less armoured.

TIMOTHY MCDONALD: So is it likely that most of these smaller crocodiles at some point kind of died off? Were they an evolutionary dead end?

ERIC ROBERTS: This group did go extinct and they went extinct probably give or take about 50 or 60 million years ago. So yes ultimately they did go extinct. I mean we wouldn't say that they were unsuccessful because actually they're incredibly successful for their time. But they're not the group that went on to lead to the modern crocodiles that we think of today.

TIMOTHY MCDONALD: You mentioned earlier that these particular creatures were on the southern super-continent of Gondwana which, you know, broke up and became other continents later on, is it likely that at some point we might find some relics of these creatures in Australia?

ERIC ROBERTS: I think that's very likely in the cretaceous age rocks of Australia, I think it's very likely. They've been found in South America, Madagascar and even parts of Asia, at least similar animals. And so we would very much expect them to be in Australia as well.