Australian fossils could date back 16 million years

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Researchers from the Australian Museum, the University of Canberra and University of NSW have published a paper about the discovery of an ‘exceptional quality’ fossil site near the town of Gulgong.

The paper, published in Science Advances, includes an analysis of animal and plant fossil samples found at the site known as McGraths Flat in the Central Tablelands. 

The fossils are estimated to be between 11 and 16 million-years-old, placing them in the Miocene Epoch (~23–5 million years ago). It is believed that during this time the Australian continent drifted northwards after separating from Antarctica and South America.

Australian Museum chief scientist Professor Kristofer Helgen said that the site offered a picture of outback Australia during a time where the fossil record has been scant.

“Australia is the most unique continent biologically, and this site is extremely valuable in what it tells us about the evolutionary history of this part of the world,” Helgen said.

“It provides further evidence of changing climates and helps fill the gaps in our knowledge of that time and region.”

Paleontologist Dr Matthew McCurry (pictured) said that an abrupt change in climate around 14 million years ago caused widespread extinctions in Australia, followed by more arid conditions across the continent.

“The fossils we have found prove that the area was once a temperate, mesic rainforest and that life was rich and abundant here in the Central Tablelands, NSW,” he said of a collection of fossil specimens including rainforest plants, insects, spiders, fish and a bird feather.

Some of the images even revealed animals' last meals, such as fish, larvae & a partially digested dragonfly wing preserved inside fishes' bellies.
| Dr @MatthewRMcCurry from @austmus and @unswbees in @LiveScience.https://t.co/ARW3TawHWO

— UNSW Science (@UNSWScience) January 9, 2022

Fossils were first discovered at the site in 2017. A team of researchers spent the last three years secretly excavating the Lagerstätte site of McGraths Flat, meaning that it is one of a few spots in Australia classified as having fossils of exceptional quality. 

Using stacking microphotography and a scanning electron microscope (SEM), the researchers were able to image individual cells of plants and animals and sometimes even very small subcellular structures from the fossil samples.

With the discovery of melanosomes (subcellular organelles that store the melanin pigment) in the fossils, the researchers have also been able to reconstruct the colour pattern of bird feathers and fish scales.

The University of Canberra’s Associate Professor Michael Frese said the analysis also demonstrated interactions between the ancient species.

“We have fish stomach contents preserved in the fish, meaning that we can figure out what they were eating. 

“We have also found examples of pollen preserved on the bodies of insects so we can tell which species were pollinating which plants,” Frese said.

The scientists believe that the reason the fossils may be so well preserved is because they were extracted from the iron-rich goethite rock. 

McCurry said that this new analysis suggested the fossils formed when groundwaters drained into a billabong. This event was then followed by a precipitation of iron minerals encasing organisms that were living in (or may have fallen into) the water.

“Many of the fossils that we are finding are new to science and include trapdoor spiders, giant cicadas, wasps and a variety of fish,” McCurry said.

“Until now it has been difficult to tell what these ancient ecosystems were like, but the level of preservation at this new fossil site means that even small fragile organisms like insects turned into well-preserved fossils.”

The costs of field work for this project were funded by a donation from the descendant of English paleontologist Robert Etheridge who joined the Australian Museum in 1887. Etheridge went on to become curator of the museum. 

Australian Museum CEO Kim McKay said that Etheridge’s contributions helped to enhance the museum collections. He was also responsible for launching a series of program expeditions that continue to this day.

“There has been a long tradition at the AM of significant, scientific discovery.  It is great to see that this continues with Dr McCurry’s work, which is directly linked to our earlier palaeontologist, curator and director, Robert Etheridge,” McKay said.