‘A Rosetta Stone’: Australian Fossil Site A Shining Window to 15m-Year-Old Rainforest | Fossils


TAustralian paleontologist Matthew McCurry was looking for Jurassic fossils when a farmer passed by with news of something he had seen in his enclosure – a fossilized leaf in a piece of hard brown rock.

The fossil leaves aren’t usually anything to write home about, but the location was close, so McCurry and his colleague Michael Frese went to take a look.

What they found in that dusty enclosure near the NSW town of Gulgong five years ago has left paleontologists – at least those who knew the secret – in awe.

Embedded in the rocks are the inhabitants of a rainforest that existed in this now dry and barren place some 15 million years ago.

“There’s a whole ecosystem preserved,” says McCurry, curator of paleontology at the Australian Museum and senior lecturer at the University of New South Wales.

As their hammers slit through iron-rich rocks, thousands of fossils have been revealed – from flowering plants and fruits and seeds, to insects, spiders, pollen and fish. There will be dozens of new species.

The research team is looking for insect fossils at the site; on their first visit, McCurry and Frese found tiny aquatic insects preserved in the rock. Photograph: Salty Dingo / Courtesy Australian Museum
A fossilized leaf from the new McGraths Flats fossil site, NSW, Australia
A fossilized leaf found in iron-rich rocks at the site. The vast array of leaf fossils allowed the team to estimate the region’s climate. Photograph: Salty Dingo / Courtesy Australian Museum

McCurry and his colleagues revealed the site and their first findings in the journal Science Advances on Saturday Australian time.

“Paleontologists around the world are going to drool when they see this article,” said Professor John Long, a famous Flinders University fossil hunter who got a glimpse of some of the fossils a year ago.

Such an array of specimens in one location allowed Australian scientists to paint an incredibly detailed picture of a little-known ecosystem from a period known as the Middle Miocene – a time just before the continent dries up to be this that it is today.

In addition to the large number of different specimens at the site – known as the McGraths Flat – it is the pristine preservation of the fossils that provides an unprecedented depth of information.

Under a microscope, there are details down to less than a micron in width (a spider’s thread is about three microns).

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

A McGraths Flat Fossil Trap Spider
“You have whole organisms… soft tissue… cellular preservation. There is a spider with its beautifully preserved respiratory system. Photograph: Michael Frese / Courtesy Australian Museum

Since that first visit, McCurry and his colleagues have unearthed a treasure trove of fossils. When rocks are shattered, they tend to split fossilized remains in half like an instant autopsy, revealing internal organs and tissues.

The stomachs of fish are so well preserved that McCurry says they can see what this fish ate – around 15 million years ago – in the moments before it disappeared.

“We can see the food in the stomach, like a dragonfly wing. But generally, they are insect larvae, ”he says.

Long saw some of the fossils last year when he visited McCurry at the Australian Museum.

“Fossils are often preserved in the form of pieces or fragments. Every once in a while you might get an entire organism. But it’s really an exceptional preservation, ”he says.

“You have whole organisms… soft tissue… cellular preservation. There is a spider with its beautifully preserved respiratory system. It is a Xanadu.

“There is all the diversity with a wide variety of organisms, from fungi to plants and fish, and there is also their interaction. There is evidence of behavior. It has all the attributes of a world-class fossil deposit, of which we have very, very few in Australia. “

“It’s a bit of a Rosetta Stone for the complete ecology of this Middle Miocene environment. We don’t have any other window into this period that tells us what this part of Australia looked like. “

Lucky fossils

New fossil sites are rare finds, and this one was almost missed. McCurry admits he’s walked past at least once, oblivious to what was there.

On his first visit with Frese, they found rocks rich in iron, unusually difficult to split, and of a type not known for fossil preservation.

But immediately, the couple found what they thought were aquatic insects. Using a microscope Frese had in his car, they could see tiny preserved midges. “It was then that we realized how special the fossils were,” says McCurry.

Associate Professor Michael Frese splits rocks for fossils at McGraths Flats, NSW, Australia
Associate Professor Michael Frese, who has been examining the fossils for several years, says he is blown away by their details. Photograph: Salty Dingo / Courtesy Australian Museum

The discovery of fossilized pollen has enabled scientists to accurately date the site.

Little is known about ecosystems from the mid-Miocene period.

McCurry says there will likely be “dozens, if not hundreds” of species new to science that have already been collected. Researchers have found probable new species preserved in the rock deposit between 50 cm and 80 cm thick at a rate of more than one per day. There have been eight excavations on the ground so far.

An electron microscopic image of a single pentagonal pollen grain
Pollen grain of Nothofagidites. This artificially colored scanning electron microscopy image shows a fossil pollen grain (Nothofagadites cf. deminitus), indicating that Nothofagus plants (and the Mesic rainforests) had a larger geographic area in the Miocene than today. Photograph: Michael Frese / Courtesy Australian Museum

Even though only two square meters are searched each time, around 2,000 specimens have been collected. Now follows the careful process of checking everyone against known records of flora and fauna.

Using the analysis of the vast array of plant leaves at the site, the team was even able to estimate the region’s climate. The warm months were around 26C and the cool months as low as 7C.

Almost a meter of rain is said to have fallen in a month during the rainy season – the region’s modern climate is warmer but much drier, with the wettest month averaging just 70mm.

Fossil feather

While much of the team reviews the vast array of flora and fauna, Dr Jacqueline Nguyen, an expert on bird evolution at the Australian Museum, mainly focused on the only evidence found so far. birds that were in the rainforest. . That is, a single fossilized feather the size of a fingerprint.

“Fossilized feathers are incredibly rare,” she says. “Most are from the Cretaceous, but from the Miocene, we only have this one. I am super excited.

The fossil feather is so detailed that Nguyen and his colleagues were able to see the parts of the cells that give the feather its color. This feather – likely from the bird’s body rather than the wing – was likely dark or iridescent.

“Even though it’s just a feather, it’s a tantalizing hint of what’s to come. Maybe we’ll find a bird skeleton.

A fossilized feather, which appears yellow against the brown rock it's in
“Fossilized feathers are incredibly rare,” explains Dr Jacqueline Nguyen. In it, roughly the size of a fingerprint, parts of the cells that gave the pen its color were identified. Photograph: Michael Frese / Courtesy Australian Museum

Frese, a trained virologist, has been examining fossils under a microscope for several years.

“I was blown away by the details,” he says. “I like the way the fossils look. Usually you only see the surface, but here it always splits in half and you see the inside of a spider leg or the inside of the pollen.

The secret to fossil preservation is the subject of some debate, but McCurry believes it would have happened over hundreds of years rather than in a sudden event.

Iron-rich water, possibly from nearby outcrops, could have flowed into a shallow billabong, periodically de-oxygenating the water, killing organisms or trapping flora and fauna in transforming sediments. in rocks found on the ground.

McCurry admits he’s relieved to be able to speak to the world of discovery.

“It’s been a marathon,” he says. “This is a really important discovery and it will keep us going for a long time.”


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