In the small southeast QLD town of Murgon,scientists have spent decades excavating what appears to be an ordinary clay pit in a local grazier’s backyard. Beneath the surface sits one of Australia’s earliest fossil-bearing locations, a site that provides a rare look into a time when the continent was still part of a much larger supercontinent.

An international research group led by the Institut Català de Paleontologia Miquel Crusafont (ICP), working with UNSW Sydney, has now identified these ancient crocodilian eggshells. The team confirmed they are the oldest ever recovered in Australia.

The fragments have been formally named Wakkaoolithus godthelpi. They once came from mekosuchine crocodiles, an extinct group that dominated waterways about 55 million years ago. Australia’s modern freshwater and saltwater crocodiles onyl appeared far later, roughly 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.”

Unusual Behaviors in Ancient Mekosuchine Crocodiles

unlike today’s crocodiles, mekosuchines occupied a surprising range of ecological roles.

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

Evidence from younger mekosuchine fossils supports this interpretation. These fossils were found in 25-million-year-old deposits at the Riversleigh World Heritage Area in Boodjamulla National Park on Waanyi country in northwestern QLD.

Some river-dwelling species at Riversleigh reached lengths of at least five meters. Prof. Archer says some were likely semi-arboreal as well.

“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.”

Eggshells as a Tool for Reconstructing Ancient Environments

Panadès i Blas highlights the scientific value of eggshells in reconstructing ancient life.

“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 samples were studied using both optical and electron microscopes. The eggshell microstructure indicates that these crocodiles likely nested along the edges of a lake and adjusted their reproductive strategies as conditions shifted over time.

Coauthor Dr. Michael Stein suggests that mekosuchines may have lost much of their inland habitat as the region dried. They would have been pushed into smaller waterways, where they had to compete with newly arrived crocodiles as well as cope with shrinking resources.