Australia’s oldest crocodile egg shells have been found in Queensland

In south-east Queensland, about 250km from Brisbane, lies the small town of Murgon. Located in Waka Waka Country, it is home to approximately 2,000 people.

From the 55-million-year-old soils there, archaeologists have unearthed many valuable fossils over the decades. These include the world’s oldest fossil songbirds, the only known fossil of salamanders in Australia and the oldest fossil marsupial in Australia.

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

These eggshells now serve as the basis for a new eggshell type, Vacuololithus godthelpii. They belong to the oldest member of the now extinct group of crocodiles known as the mecosuchines. And they not only offer a new look at their evolution.

A tree-climbing crocodile

Mycosuchines were Australia’s own unique, endemic branch of the crocodile family. They dominated the continent’s inland waters 55 million years ago. They were part of a group of species that included fish, true crocodiles, gharials and caimans.

But they represent a much older branch than the saltwater and freshwater crocs found in Australia today. These modern species made their way to the continent much later, as it came into contact with Southeast Asia about five million years ago.

In the 1980s, fossil finds began to turn up at sites such as the Murgon and Riverslug World Heritage Areas in Queensland and the Alkota sites in the Northern Territory. Since then, paleontologists have been able to piece together a good picture of the diversity of mycozoans. It was much more than what we see today, accounting for ten extinct genera now.

These fossils preserve a rich evolutionary history, and in particular a trend towards land-based hunting around 33 million years ago.

This diversity includes the likes of Quincana, a large land-based crocodile with narrow jaws, and dwarf species such as Trilophosuchus that may have been positioned to fill the niche of a tree-climbing predator.

The latter case was originally suggested by paleontologist Paul Willis based on unusual musculature at the back of the skull of Trilophosuchus. Although hotly debated, Willis suggested that this would have allowed Trilophosuchus to raise its head and scan the three-dimensional environment of the canopy.

Reading eggshells

However, new research has taken a look at one of the oldest species of mecosuchians in Macbara. It grows up to two meters long and is thought to have fed on fish and softshell turtles.

Researchers from the University of New South Wales, led by Henk Godthelp and Michael Archer, uncover fragments of an eagle at Mergon, a relatively rare find. Surprisingly little work has been done in the field of analyzing crocodile eggshells.

Xavier Panades i Blas from the Institut Català de Palaeontologia at the University of Barcelona took up the challenge to explore the preserved microstructure of the shell with high-resolution microscopy.

What he found was interesting. Cumbra eggshells have their own unique microstructural features, which are still preserved after 55 million years.

These features are known for the microstructures that we have evolved among modern crocodiles and fish. However, putting things into formal context will take a lot of work.

Still, these eggshells may provide a valuable new avenue for understanding how mecosuchians fit into the larger evolutionary picture that spans Australia, Asia, Africa, and the Americas.

A window into a pristine ecosystem

Beyond evolution, these eggshells are an insight into the environment that existed in Mergans 55 million years ago. Crocodile reproduction is deeply influenced by their local environment and a complex mix of nesting strategies appears in response to modern species.

In the case of Kumbra eggshells, there is little sign of bacterial degradation.

This suggests that nesting merguns may experience periods of dryness due to the primary nature of the surrounding wetlands.

Although mecosuchines enjoyed a much larger range of territories than our modern crocodiles, they eventually experienced a considerable contraction as the continent accelerated.

Between this and the decline of large prey, mycoschines eventually became extinct on the Australian continent.

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