Australia’s oldest crocodile eggshells found in Queensland

In southeast Queensland, about 250 kilometers from Brisbane, is the small town of Murgon. Located in Wakka Wakka country, it is home to approximately 2,000 people and is one of the most important fossil sites in the world.

From the 55 million year old clays, paleontologists have uncovered a series of precious fossils over several decades. These include the world’s oldest fossil songbirds, Australia’s only known salamander fossils, and Australia’s oldest marsupial fossil remains.

And the site continues to house ancient treasures. In a new study, published today in the Journal of Vertebrate Paleontologymy colleagues and I report the discovery of the oldest crocodilian eggshells ever found in Australia.

These eggshells now serve as the basis for a new type of eggshell, Wakkaoolithus godthelpi. They belong to the oldest known member of a now-extinct group of crocodiles known as mekosuchines. And they offer a new look not only at their evolution, but also at the forest-fringed wetlands in which they lived.

Crocodiles climbing trees

Mekosuchines were the unique local branch of the crocodile family in Australia. They dominated the continent’s interior waters 55 million years ago. They were part of the group of species that includes alligators, true crocodiles, gharials and caimans.

But they represent a much older branch than the saltwater and freshwater crocodiles found in Australia today. These modern species arrived on the continent much later, when they came into contact with Southeast Asia around five million years ago.

In the 1980s, fossil discoveries began to increase at sites such as Murgon and the Riversleigh World Heritage Area in Queensland, and Alcoota in the Northern Territory. Since then, paleontologists have been able to draw up a good picture of the diversity of mekosuchines. This was much higher than what we see today, with ten extinct genera now listed.

These fossil discoveries preserve a vigorous evolutionary history, and in particular a trend toward terrestrial hunting around 33 million years ago.

This diversity includes species like the Quinkana, a large, narrow-jawed land crocodile, and dwarf species such as Trilophosuchus that might have been able to fill the niche of a tree-climbing hunter, a sort of “falling crocodile.”

The latter case was initially suggested by paleontologist Paul Willis based on the unusual musculature at the back of Trilophosuchus’ skull. Although hotly debated, Willis suggested that this would allow Trilophosuchus to hold its head high and navigate the three-dimensional environment of the canopy.

Reading eggshells

The new study, however, looks at one of the oldest genera of mekosuchines, Kambara. It measured up to two meters long and is thought to have fed on fish and softshell turtles.

At Murgon, University of New South Wales researchers led by Henk Godthelp and Michael Archer discovered eggshell fragments, a relatively rare find. Surprisingly little work has been done in the area of ​​crocodile eggshell analysis.

Xavier Panadès I Blas from the Institut Català de Paleontologia at the University of Barcelona took on the challenge of exploring the preserved microstructure of the shell using high-resolution microscopy.

What he discovered was intriguing. Kambara eggshells have their own unique microstructural features, still preserved after 55 million years.

These features differ from what we know about the microstructures that evolved among modern crocodiles and alligators. However, it will take a lot more work to put things formally into context.

Nonetheless, these eggshells could provide a valuable new avenue for understanding how mekosuchines fit into the broader evolutionary framework that spans Australia, Asia, Africa, and the Americas.

A window into an ancient ecosystem

Beyond evolution, these eggshells provide insight into the environment that existed in Murgon 55 million years ago. Crocodile reproduction is intimately linked to their local environment and modern species display a complex mix of nesting strategies in response.

In the case of Kambara eggshell, there is little evidence of degradation by bacteria.

This suggests that the nest may have experienced periods of drought due to the ephemeral nature of the surrounding wetlands in Murgon.

Although mekosuchines enjoyed a much wider range of territories than our modern crocodiles, they ultimately experienced considerable contraction as the continent became increasingly arid.

Between this and the decline of large prey, mekosuchines eventually disappeared from the Australian continent.

This article is republished from The Conversation under a Creative Commons license. Read the original article.