55-Million-Year-Old Backyard Fossil Find Shocks Paleontologists

The discovery of Australia’s oldest known crocodile eggshells is giving UNSW scientists new insight into the animals and ecosystems that existed millions of years ago, long before Australia separated into its own island continent.

In the backyard of a grazier in the small southeast QLD town of Murgon, researchers have spent decades digging in what appears to be an ordinary clay pit. Hidden inside the clay, however, is one of Australia’s oldest fossil localities, offering a rare glimpse into a time when the continent was still joined to Antarctica and South America.

An international research group led by the Institut Català de Paleontologia Miquel Crusafont (ICP), with contributions from UNSW Sydney, has now identified the oldest crocodilian eggshells ever discovered in Australia.

The newly described fragments, named Wakkaoolithus godthelpi, once came from mekosuchine crocodiles. These now extinct crocs dominated inland wetlands about 55 million years ago. Australia’s modern freshwater and saltwater species only arrived much later, around 3.8 million years ago.

“These eggshells have given us a glimpse of the intimate life history of mekosuchines,” says the study’s lead author Xavier Panadès i Blas.

“We can now investigate not only the strange anatomy of these crocs, but also how they reproduced and adapted to changing environments.”

From swimmers to tree-climbing hunters

Unlike modern crocodiles, mekosuchines occupied highly unusual ecological roles.

“It’s a bizarre idea,” says UNSW paleontologist Professor Michael Archer. “But some of them appear to have been terrestrial hunters in the forests.”

Evidence for this comes from a diverse set of younger mekosuchine fossils found in 25-million-year-old deposits in the Riversleigh World Heritage Area in Boodjamulla National Park on Waanyi country in northwestern QLD.

Prof. Archer explains that some riverine species grew to at least five meters long.

“Some were also apparently at least partly semi-arboreal ‘drop crocs’,” he says.

“They were perhaps hunting like leopards – dropping out of trees on any unsuspecting thing they fancied for dinner.”

A delicate time capsule

Panadès i Blas notes that eggshells are often overlooked in vertebrate paleontology.

“They preserve microstructural and geochemical signals that tell us not only what kinds of animals laid them, but also where they nested and how they bred,” he says.

“Our study shows just how powerful these fragments can be. Eggshells should be a routine, standard component of paleontological research – collected, curated, and analyzed alongside bones and teeth.”

The Murgon eggshell pieces were examined using optical and electron microscopes. Their microscopic features indicate that the crocs laid their eggs along the edges of a lake and that their reproductive strategies adjusted to shifting environmental conditions.

Coauthor Dr Michael Stein proposes that mekosuchine crocodiles may have gradually lost much of their inland habitat as arid regions expanded. They were eventually pushed into shrinking waterways, where they not only faced new crocodile species arriving in Australia but also dwindling numbers of their large prey.

Dr Stein says the Murgon lake was surrounded by a lush forest.

“This forest was also home to the world’s oldest-known songbirds, Australia’s earliest frogs and snakes, a wide range of small mammals with South American links, as well as one of the world’s oldest known bats,” he says.

A story with teeth

Prof. Archer says the discovery within the Tingamarra deposit at Murgon is part of a much bigger story – one that enriches the understanding of ancient ecosystems before Australia became an independent continent.

He recalls finding a bizarre crocodilian jaw fragment in 1975 in the Texas Caves of southeastern Queensland.

While this has since been confirmed as a mekosuchine croc, at the time it seemed so strange to Prof. Archer that he didn’t suspect it was a crocodile. It seemed to be a reptile – but one with dinosaur-like teeth. He was so baffled that he decided to consult Professor Max Hecht – a reptile specialist at the American Museum of Natural History.

“When he saw it, Max nearly dropped his coffee cup,” Prof. Archer says.

“It closely resembled another kind of extinct croc with dinosaur-type teeth that had been found in South America.

“That was the first realization that crocodiles with teeth like this were also part of the older record in Australia.”

Prof. Archer says he and his colleagues have been excavating in the Murgon area since 1983, literally in the backyard of excited local residents.

“That year, UNSW colleague Henk Godhelp and I drove to Murgon, parked the car on the side of the road, grabbed our shovels, knocked on the door and asked if we could dig up their backyard,” Prof. Archer says.

“After explaining the prehistoric treasures that might lay under their sheep paddock and that fossil turtle shells had already been found in the area, they grinned and said ‘of course!’.

“From subsequent excavations, that’s where the eggshell pieces came from.

“And, quite clearly, from the many fascinating animals that we’ve already found in this deposit since 1983, we know that with more digging there will be a lot more surprises to come.”

Informing conservation

For Prof. Archer, discoveries like this are more than just glimpses of a vanished past – they’re sometimes reminders that Australia’s fossil record can reveal important clues about how to save some of today’s threatened species.

He has been working with a multi-institutional team on the ‘Burramys Project’ to bring the Mountain Pygmy-possum – Burramys parvus – back from the edge of extinction.

This species, native to eastern Australia’s alpine regions, is critically threatened as pressure from climate change mounts. However, Prof. Archer’s team discovered that its prehistoric relatives, evolving over the past 25 million years, have always thrived in temperate lowland rainforests – including those that covered the Riversleigh area between 25 to 12 million years ago.

This led to the theory that the immediate ancestors of today’s Mountain Pygmy-possum likely followed rainforests as they moved up into alpine areas during a warm, wet interval during the Pleistocene Epoch. But when the climate in the alpine zone changed and cooled, they had to develop evasive behaviors like hibernation to survive increasingly inhospitable conditions.

A few years ago, Prof. Archer’s team – working with Trevor Evans, the manager of Secret Creek Sanctuary, and with donations from many organizations, including the Prague Zoo in the Czech Republic – built a breeding facility in an area of non-alpine rainforest near the town of Lithgow.

Today, Mountain Pygmy-possums are flourishing within that non-alpine sanctuary – just as Prof. Archer says the fossil record predicted they would.

As climate change increasingly threatens the existence of more and more species, he says not all stories need be about the gloom and doom of disasters triggered by climate change.

“The Burramys Project is a demonstration that, at least in some cases, we can develop strategies to save endangered species,” Prof. Archer says.

“Clues from fossil records matter,” he says.

“Not just to understand the past, but also to help secure the future.”

Reference: “Australia’s oldest crocodylian eggshell: insights into the reproductive paleoecology of mekosuchines” by Xavier Panadès I Blas, Àngel Galobart, Michael Archer, Michael Stein, Suzanne Hand and Albert Sellés, 11 November 2025, Journal of Vertebrate Paleontology.
DOI:10.1080/02724634.2025.2560010

The new croc species’ name, Wakkaoolithus godthelpi, acknowledges, with permission, the Wakka Wakka First Nations people, on whose Country the fossils were found. The second part of the name recognises Henk Godthelp, who was part of the UNSW palaeontologist crew along with Prof. Archer, Professor Sue Hand and many other research staff and students.

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