Known as Wakaorisus Godterupi, this eggshell type belongs to the mecostine crocodile, which represents the oldest crocodile eggshell ever discovered in Australia.

The now-extinct Mecostinae (Mecostinae) represented a distinctive local branch of Australia’s crocodilian family.

These creatures dominated the continent’s inland waters approximately 55 million years ago during the early Eocene epoch.

They were part of a broader group that included true crocodiles, gharials, and caimans.

However, mecostins represent an older lineage than the saltwater and freshwater crocodiles currently found in Australia.

Modern species arrived much later, migrating to the continent from Southeast Asia about 5 million years ago.

Unlike contemporary crocodiles, mecostins occupied a rather unusual ecological niche.

“It’s a peculiar notion, but evidence suggests that some of them were terrestrial hunters in forested areas,” remarked Professor Michael Archer from the University of New South Wales.

“This is indicated by a wide range of juvenile mecostin fossils previously found in 25-million-year-old deposits in the Riverslea World Heritage Area, Boojamulla National Park, Wahnee Country, in north-west Queensland.”

“Some species living in those rivers reached lengths of over five meters, including ‘drop crocodiles’ that were likely partially arboreal.”

“They might have hunted similarly to leopards, dropping unsuspecting prey from trees.”

The eggshells of Wakaorisus Godterupi are among the oldest known members of the Mecostinidae clade.

“These eggshells offer a glimpse into the life history of Mecostine,” said paleontologist Dr. Panades y Blas.

“We can now explore not only the unique anatomy of these crocodiles but also their reproductive behaviors and adaptations to environmental changes.”

The researchers examined Wakaorisus Godterupi shell fragments using both optical and electron microscopes.

The microstructure indicates that these crocodiles laid eggs at the water’s edge, employing a reproductive strategy suited to variable conditions.

“The Mecostine crocodile may have lost extensive inland territory to dryland encroachments, ultimately competing with new arrivals in Australia, dwindling megafauna-sized prey, and diminishing waterways,” noted University of New South Wales palaeontologist Dr. Michael Stein.

“Lake Murgon was surrounded by lush forests. I was at home too where fossils of the world’s oldest songbird, Australia’s oldest frog and snake, various small mammals connected to South America, and even one of the oldest bats have been found.”

The researchers assert that fossil eggshells are an underutilized asset in vertebrate paleontology.

“They retain microstructural and geochemical evidence that reveals not only the type of animal that laid them but also where they nested and how they bred,” said Dr. Panades y Blas.

“Our research demonstrates the significance of these fragments.”

“Eggshells should be a standard element of paleontological investigations, collected, categorized, and analyzed alongside bones and teeth.”

These findings are published this week in the Journal of Vertebrate Paleontology.

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Xavier Panades Brass et al. Australia’s oldest crocodile eggshell: insights into the reproductive paleoecology of mecostin. Journal of Vertebrate Paleontology published online on November 11, 2025. Doi: 10.1080/02724634.2025.2560010