The Central Tablelands of Australia, located hundreds of miles northwest of Sydney, are dominated by grasses and stunted trees at the moment. Although some of the region’s rusty rocks are difficult to see, scientists have just found that they contain remains of luxuriant rainforests that blanketed the area 15 million years ago, during the Miocene Epoch.
Despite the fact that McGraths Flat is not Australia’s unique Miocene deposit, the discovery of these new fossils is a windfall to palaeontology because of their exceptional preservation. Over the course of three years, palaeontologists have unearthed flowers, insects, and even a wispy feather from a bird’s wing.
This 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 research. The scientists’ discoveries were published Friday in the journal Science Advances and help reconstruct Australia’s Miocene rainforest in great detail.
A river ripped through the rainforest 15 million years ago, leaving an oxbow lake (known as a billabong in Australia) in its wake at McGraths Flat, where it is still visible today. This stagnant lake, which was almost completely devoid of oxygen, held scavengers at away, enabling plant debris and animal corpses to accumulate. Due to the low pH of the billabong, iron-rich rainwater from adjacent basalt mountains seeped into the pool, causing the iron to precipitate and encapsulate the organic stuff within. Consequently, the fossils in McGraths Flat have been preserved in a thick, iron-rich rock known as goethite, which is found in the area.
According to Dr. Hocknull, this type of fossilisation is unusual in nature. Because high-quality fossils are uncommon in igneous rocks, palaeontologists tend to ignore them while studying them. The fossils from McGraths Flat, on the other hand, demonstrate that goethite, which is abundant in Australia, may produce fossils of exceptional quality.
Because of their iron-tinted origins, many of the fossils found in McGraths Flat have a metallic sheen to them that makes them stand out. It is swarming with petrified insects in addition to the exquisite flora that may be seen on the goethite. After splitting off the brick-colored slabs of stone, the researchers uncovered a little zoo of enormous cicadas, dragonflies, and parasitic wasps that they had never seen before. And several of them have been exceptionally well preserved – some ancient flies still have the intricate impressions of their complex eyes.
More than a dozen archaic arachnids have also been discovered at the site. Even while insects have tough exoskeletons, according to co-author Michael Frese, a virologist and palaeontologist at the University of Canberra who is also a co-author of the paper, spiders have exoskeletons that are “squishy sacks of liquid.” As a consequence, the fossil record of spiders in Australia was almost non-existent prior to the discovery of McGraths Flat.
Observing links between species was made possible because to the very well preserved fossils, which, according to Matthew McCurry, curator of palaeontology at The Australian Museum and the study’s main author, is something that is frequently difficult to discern from fossil sites. For example, the researchers discovered parasites attached to the tail of a fish and a nematode that had penetrated the body of a longhorn beetle.
According to the pollen analysis, the rainforest was bordered by drier habitats, indicating that McGraths Flat is likely to be a remnant area of a once-larger forest system. Dr. McCurry believes that this makes sense in light of the climatic shifts that have occurred over the Miocene.
Australia was moving northward, away from Antarctica, during the time these insects rushed about the billabong’s iron-tainted water. Because of its travels, the temperature of the planet became considerably dryer, forcing the rainforests to recede and triggering massive extinctions.
This site, according to the researchers, gives a unique opportunity to see firsthand the impact of this rapid temperature shift on certain species inside the tropical rainforest ecosystem. For example, certain insects discovered at McGraths Flat have to withstand drier circumstances, but others are currently only found in the last remaining pockets of rainforest in northern Australia.
Using these ancient ecosystems, Dr. McCurry and his colleagues can determine which species were better able to adapt to the changes that occurred through time. “We may be able to identify which areas would be most vulnerable to future changes,” says the researcher.
Doctor Frese said that the diversity of species preserved at McGraths Flat made it especially valuable for recreating prehistoric ecosystems.
“Our site is unique in that it contains only little fossils, but I believe that in the end, it will provide us with more information about what has occurred in the ecosystem,” Dr. Frese stated. “It is not necessary to locate a one-ton horror bird in order to tell this narrative.”