Miocene fossils shed light on Australia’s ancient rainforest ecosystem

A suite of immaculately preserved fossils of plants, spiders, insects and vertebrates found at the McGraths Flat in New South Wales has given researchers an unprecedented insight into what Australia would have looked like during the Middle Miocene (16 Ma to 12 Ma). The finds were made by palaeontologists Matthew McCurry of the Australian Museum in Sydney and Michael Frese of the University of Canberra.

Thousands of fossils have been revealed in the iron-rich rocks– from flowering plants to fruits and seeds, insects, spiders, pollen and fish. One of the most remarkable was of a 4 cm long mygalomorph spider. “It’s unlike anything that we have seen alive today in Australia,” says McCurry. “One of the characteristics that’s quite different is the size of this first set of legs – it’s an extremely large spider.”

The finds have allowed the scientists to build an incredibly detailed picture of a little-known ecosystem from the Middle Miocene – a time just before the continent dried out to be what it is today. As well as the huge number of different specimens at the site, the fossils’ immaculate preservation is delivering an unprecedented depth of information.

The breathing apparatus of spiders and the contents of fish stomachs are visible. The cells that can reveal the original colour of a feather have been preserved. A sawfly was frozen in time with dozens of pollen grains attached to its head. 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.

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; warm months were about 26°C and cool months as low as 7°C. They also found that, during the three wettest and driest months of the year, rainfall was around 962 mm and 254 mm per month, respectively.

This story is based on articles in New Scientist and the Guardian. The original research was published in Science Advances.

Bill Gray