Fossils: Spider remains shed light on Australia’s ancient rainforest ecosystem


A suite of plant and animal fossils from a site in New South Wales date back around 16 million years, to a time when the region was covered in lush rainforests.

The life

January 7, 2022

Fossil of a mygalomorph spider from McGraths Flat, Australia

Michel Frese

A perfectly preserved fossil of a mygalomorph spider (Mygalomorphae) has been discovered by researchers conducting excavations at McGraths Flat, a fossil site in New South Wales, Australia. The 4 centimeter long spider (pictured above) lived around 11 to 16 million years ago when the region was dominated by rainforest.

“It’s unlike anything we’ve seen alive today in Australia,” says co-author Matthew McCurry of the Australian Museum Research Institute in Sydney. “One of the features that’s quite different is the size of that first set of legs – it’s an extremely large spider.”

A suite of equally well-preserved plant, insect and vertebrate fossils have been found at the McGraths Flat site, giving researchers unprecedented insight into what Australia would have looked like in the Miocene era.

“These are sites that even preserve the soft tissue structures inside the specimens,” says co-author Michael Frese from the University of Canberra.

By analyzing the properties of several leaf fossils from the site, McCurry, Frese and their colleagues reconstructed the region’s past climate using a computer model. The average annual temperature of the region has been estimated at around 17°C. They also found that during the wettest and driest three months of the year, rainfall was around 962 millimeters and 254 mm per month, respectively.

Additionally, the researchers found evidence of interactions between the organisms. For example, they found a freshwater mussel attached to a fish’s fin, meaning the mussel used the fish to move around and feed. They also discovered a microscopic parasitic nematode that appears to have hitched a ride on the back of a longhorned beetle.

“The degree of fossilization allows us to gain unprecedented insight into what these ancient rainforest ecosystems looked like,” says McCurry.

The site also fills a gap in knowledge of Australia’s prehistoric past, says Frese. “We didn’t have any fossil sites that would give us information about the Miocene in Australia, which is an important time period.”

“It was a time when Australia was becoming increasingly arid and most of its modern ecosystems were growing,” says McCurry. “It’s Australia’s origin story, in a way.”

Journal reference: Scientists progressDOI: 10.1126/sciadv.abm1406

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