Scans of tiny 13.5-million-year-old Aussie crocodile suggest it may have spent most of its time on land

A tiny crocodile which called north-western Queensland home 13.5 million years ago has revealed its secrets to University of Queensland (UQ) researchers.

The palaeontologists used high-tech methods to scan the fossils of the creature to uncover previously unknown details about its anatomy. The findings are published in the Journal of Anatomy.

Named in 1993, the ancient croc is called Trilophosuchus rackhami, meaning Rackham’s three-crested crocodile. It was named after Alan Rackham, the current manager of the Riversleigh Fossil Discovery Centre at Mt Isa in northwest Queensland.

“By micro-CT scanning the beautifully preserved skull, we were able to digitally separate each bone,” says author Jorgo Ristevski, a PhD candidate at UQ.

“We estimated that at adulthood, Trilophosuchus rackhami would have been between 70 and 90 centimetres long and weigh one to two kilograms, which was very small compared to most present-day crocs. This was a truly unique looking croc, with a short snout and three distinct ridges on the top of its skull.”

Trilophosuchus lived in the middle of the geological period known as the Miocene which lasted from around 23 million to 5 million years ago.

At the beginning of the Miocene, Australia separated from Antarctica. Over the next millions of years, the Australasian continental plate would travel northward, pushing up against the islands of southeast Asia. Meanwhile, Antarctica would inch further south, growing colder.

Australia’s climate in the Miocene was much more humid and wetter than it is today, though it would get dryer by the late Miocene as more of Earth’s atmospheric moisture was being trapped in the ice sheets of Antarctica which were beginning to form.

Even so, in the time that T. rackhami lived, northern Australia was still covered in lush tropical rainforest. It was a vibrant time of rich plant and animal life. Northern Australia would have resembled today’s Amazon.

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Ristevski says palaeoneurology – the study of fossil brain and nervous systems – can provide key insights into the animal’s evolution, anatomy and behaviour.

“For one of the studies, I digitally reconstructed the brain cavity of Trilophosuchus rackhami and found that it resembles that of some distantly related and potentially terrestrial extinct crocs from Africa and South America,” Ristevski explains.

By scanning the animal’s skull, Ristevski was able to compare it to other known extinct and living crocodilians. His results suggest that the T. rackhami may have spent a lot of its time on the forest floor rather than in the water.

“We were quite surprised because evolutionarily speaking, Trilophosuchus rackhami is more closely related to today’s crocs. The fact it resembles other potentially terrestrial crocodiles may indicate that Trilophosuchus rackhami spent more time on land than most living crocs.”

Head of UQ’s Dinosaur Lab, Associate Professor Steve Salisbury, says Australia had a rich array of prehistoric crocs up until very recently. “Trilophosuchus rackhami was certainly one of the cutest,” says Salisbury.

“If we could travel back in time to north Queensland 13 million years ago, not only would you need to watch out for crocodiles at the water’s edge, but you’d also have to make sure you didn’t step on them in the forest.”

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