Time Capsules of the Past: Exploring Exquisite Fossils from an Ancient Australian Forest

A new trove of plant, insect, fish and other fossils offers an unprecedented snapshot of Australia’s wetter, forest-dominated past.

McGraths Flat in New South Wales contains thousands of beautifully preserved specimens of flowering plants, ferns, spiders, insects and fish, vertebrate paleontologist Matthew McCurry and colleagues report January 7 in Science Advances.

Images of the fossils’ soft tissues, captured with scanning electron microscopy, reveal them in astonishing detail, from the facets of a crane fly’s compound eye to phantom midges trapped in a fish’s stomach.

Once upon a time, Australia was carpeted with rainforests. During the Miocene Epoch, about 23 million to 5 million years ago, Earth underwent a climatic upheaval. For Australia, that meant drying out, with shrubs, grasses and deserts expanding into once-lush territory. McGraths Flat formed during that transition, between 16 million and 11 million years ago. At the time, it was part of a temperate forest around a small lake, new analyses of fossil pollen and leaves suggest.

The fossils were cemented within fine layers of goethite, an iron hydroxide mineral that probably formed as acidic groundwater circulated through basalt rocks, leaching out their iron, the researchers suggest. As the groundwater seeped into the lake, the iron became oxidized and precipitated out as goethite particles. The tiny particles encased plants, insects and other creatures in the water — possibly while they were still alive — and later replaced some of the organisms’ interior structures.

“Until we studied these fossils, we wouldn’t have thought to look for well-preserved fossils in this type of rock,” says McCurry, of the Australian Museum Research Institute in Sydney. At other fossil-rich sites known for preserving soft tissues, such as Canada’s Burgess Shale or China’s Qingjiang biota, the organisms tend to be encased in the sort of soft mud found at the bottom of a sea (SN: 11/28/11; SN: 3/21/19). But, McCurry says, this site shows that goethite “has everything you need to create exceptionally well-preserved specimens.”