Grasslands and stunted trees now dominate Australia’s Central Tablelands, hundreds of miles northwest of Sydney. Scientists have uncovered signs of lush rainforests that blanketed the area 15 million years ago during the Miocene Epoch in some of the area’s rusting rocks.
Despite the fact that McGraths Flat is not Australia’s sole Miocene deposit, the new fossils are a paleontological boon due to their exceptional preservation. Flowers, insects, and even a bird’s wispy feather have been discovered by palaeontologists over the last three years.
The findings, which were published in the journal Science Advances on Friday, aid in the reconstruction of Australia’s Miocene rainforest in great detail, and the site “opens up a whole new area of exploration for Australian palaeontology,” according to Scott Hocknull, a palaeontologist at the Queensland Museum who was not involved in the study.
A river ploughed through the jungle fifteen million years ago, leaving an oxbow lake (known as a billabong in Australia) in its aftermath at McGraths Flat. This sluggish lake, nearly devoid of oxygen, held scavengers at bay, allowing plant matter and animal carcasses to accumulate. The pool’s low pH allowed iron to precipitate and encapsulate the organic material as iron-rich rainfall from neighbouring basalt mountains seeped into the billabong. As a result, the fossils in McGraths Flat have been preserved in goethite, a solid, iron-rich rock.
According to Dr. Hocknull, this method of fossilisation is unusual. Paleontologists frequently miss igneous rocks because high-quality fossils are rare. The fossils from McGraths Flat, on the other hand, show that goethite, which is abundant in Australia, may produce amazing fossils.
Dr. Hocknull stated, “There is no lack of goethite.” “Essentially, we’re a rusting country.”
Many of the fossils from McGraths Flat have a metallic sheen due to their iron-tinted origins. The goethite is teeming with petrified insects in addition to exquisite vegetation. The researchers uncovered a little menagerie of enormous cicadas, dragonflies, and parasitic wasps as they split apart the brick-colored stone slabs. Many are surprisingly well preserved, with the compound eyes of prehistoric flies imprinted in fine detail.
More than a dozen archaic arachnids have also been discovered at the site. While insects have tough exoskeletons, spiders have “squishy bags of liquid,” according to Michael Frese, a virologist and palaeontologist at the University of Canberra and a co-author of the study. As a result, before McGraths Flat, Australia’s spider fossil record was almost non-existent.
According to Matthew McCurry, curator of palaeontology at The Australian Museum and the study’s primary author, the fossils are so well preserved that palaeontologists were able to observe relationships between species, which is something that is generally difficult to discern from fossil sites. The team discovered parasites attached to a fish’s tail and a nematode that had invaded a longhorn beetle, for example.
Dr. Frese examined the rainforest’s inhabitants using an electron microscope and microphotography techniques. Dr. Frese observed a clump of pollen on the head of a fossilised sawfly while imaging it.
“We can know which flower this sawfly visited before it fell into the water and died unnecessarily,” Dr. Frese stated. “That wouldn’t be conceivable if the preservation quality wasn’t as good.”
The pollen also revealed that the rainforest was bordered by drier habitats, implying that McGraths Flat is a sliver of a once-larger forest. This makes sense, according to Dr. McCurry, given the Miocene’s climate tendencies.
Australia was migrating northward, away from Antarctica, as these insects ran around the iron-tainted billabong. Its climate dries out dramatically as it travels, causing rainforests to shrink and widespread extinctions.
McGraths Flat, according to the researchers, provides an up-close look at how this significant temperature shift impacted specific species in the rainforest ecosystem. Some insects found at McGraths Flat, for example, have adapted to drier conditions, while others are now only found in northern Australia’s last remnants of rainforest.
“We can discover which species were better able to adjust to those changes by studying these fossil ecosystems,” Dr. McCurry added. “We may be able to identify which areas are most vulnerable to future changes.”
McGraths Flat, according to Dr. Frese, was particularly beneficial for reconstructing ancient ecosystems due to the diversity of species it maintained.
“Our site is unique because it’s all little fossils,” Dr. Frese explained, “but I believe it will ultimately tell us more about what happened in the ecosystem.” “To convey this storey, you don’t need to discover a one-ton horror bird.”