Spider fossil sheds light on Australia’s ancient rainforest ecosystem

An immaculately preserved fossil of a mygalomorph spider (Mygalomorphae) has been uncovered by researchers excavating at the McGraths Flat, a fossil site in New South Wales, Australia. The 4-centimetre-long spider (pictured above) lived some 11 million to 16 million years ago when the area was dominated by rainforest.

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

A suite of equally well-preserved fossils of plants, insects and vertebrates were found at the McGraths Flat site, giving researchers an unprecedented insight into what Australia would have looked like during the Miocene Epoch.

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

By analysing 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 mean annual temperature of the area was estimated to have been around 17°C. They also found that during the three wettest and driest months of the year, rainfall was around 962 millimetres and 254 mm per month, respectively.

Additionally, the researchers found evidence of interactions between organisms. For example, they discovered a freshwater mussel attached to the fin of a fish, which means 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 longhorn beetle.

“The degree of fossilisation allows us this unprecedented insight into what these ancient rainforest ecosystems were like,” says McCurry.

This site also closes a gap in the knowledge of Australia’s prehistoric past, says Frese. “We had no fossil site that would give us information on the Miocene in Australia, which is an important time period.”

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

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