The newly discovered prehistoric rainforest fossils are amazing.

This sawfly lived in southeast Australia from160,000 years ago to110,000 years ago. Its head still contains pollen grains, which is a microcosm of ancient rainforest life.

Photo courtesy of Michael Fraser.

Michael gray Shike wrote it.

One day a few years ago, about 25 kilometers away from Gulgong, a small town in the southeast of Australia, Nigel McGrath spent a day working hard on his own land. The land was covered with heavy rocks rich in iron, which posed a threat to his farm tools, so mcgrath had to drag the loose rocks into piles by hand. At that time, he noticed them: well-preserved leaf fossils were stuffed in the rocks like impressions in stone books.

Now, scientists have confirmed that these iron stones scattered in less than half a football field contain one of the most amazing life records found in ancient rainforests so far.

The site, named McGrath Flat, was published in Science Progress magazine, and it is one of the few places in the world where the rainforest ecosystem can be traced back to Miocene, which refers to the period from 23.03 million years ago to 5.33 million years ago. During this period, the world experienced great ecological changes, and Australia began to transition from the rainforest (such as Amazon now) to the arid area of shrubs and hay we see today.

These isolated flower fossils are believed to belong to Malva, a species composed of more than 7,000 living plants, including hibiscus and cocoa. Photography: Michael Fres

There are other Miocene fossil sites in Australia, which are famous for the bones of mammals and reptiles, but these sites do not always contain small and soft substances that form the basis of ecosystems. However, there are a large number of these small fossils in mcgrath Plain, which record the amazing and diverse rainforests that grew in New South Wales from160,000 to10,000 years ago.

On the flat land in McGrath, the legs of spiders turned into fossils, and the bellies of fossilized fish were stuffed with midges. The leaves are so well preserved that researchers can even see the stomata they use to absorb carbon dioxide.

Suzanne Hand, a paleontologist at the University of New South Wales, said: "These newly discovered materials are excellent in quality and quantity, as are the biological and ecological information extracted and presented from them."

Fossils from McGrath's flat land even contain freeze-frame moments of life activities. A sawfly's head is covered with pollen. It is estimated that it has just enjoyed the nectar of a flower. The fish's tail carries a "passenger": the parasitic larva of the imperforate mussel. When it goes upstream, it feeds on the mucus of this fish.

Matthew McCurry, the first author of this new study and a paleontologist at the Australian Museum Research Institute in Sydney, said: "The preservation quality of these fossils is quite good, and we can see these ecosystems accurately and vividly, which is unprecedented."

This fossil feather (or a small part of the leaf) may come from a fern of Lygodium. Even the stomata 10 micron wide of this plant have become fossils and can be seen under the electron microscope.

There are many kinds of insects preserved in Pingdi site in mcgrath, including dragonfly larvae, which can swim freely. They are called larvae, that is, the fossils in the picture. Photography: Michael Fres

Extremely well-preserved fossils

In 20 17, mccurry and his colleagues first heard about this place from mcgrath. Aware of the potential significance of these fossils, they began to visit the site for three or four days in a row to study these flints in order to see the ancient rainforest.

The more scientists analyze this site, the more they realize how unusual the preservation of this fossil is. These fossils are buried in a very fine layer of iron oxide minerals called goethite. Fossils have been found in this kind of rocks before, but the quality of specimens in mcgrath Plain is particularly outstanding.

Freys added that this unusual fossil type makes mcgrath plain fossils particularly easy to analyze by scanning electron microscope (SEM), which is the most powerful microscope at present. Usually, samples must be plated with a thin layer of gold or platinum under scanning electron microscope, which limits the further study of these samples. Mcgrath flat stone is rich in iron and has good conductivity, so it can be directly placed under an electron microscope without any extra preparation.

Freys said: "The fossil was placed under a scanning electron microscope, just as it was when it was taken out."

The smallest fossil has made some amazing discoveries. Among the only known feather fossils in this area, researchers can see black capsules, whose shapes indicate that feathers may be black or rainbow-colored. Scientists can also see the preserved melanin in the eyes of fish fossils. They even found the scales that fell off the wings of butterflies or moths 1 1 10,000 years ago.

Under the magnifying glass, we can see that this longicorn beetle, which is about 2 cm long, has a "passenger": a small nematode.

The fossils in mcgrath Plain include a bird feather, which is very complete. Under the high magnification of electron microscope, we can see the cyst of melanin. Photography: Michael Fres

A lake submerged by molten iron

The current thinking of the research team is that the mcgrath Plain was once a river and lake, which was formed when a part of a winding river was cut off. Most of the time, the lake is quite quiet with low oxygen content and few predators. However, judging from the dozens of fish fossils found in this area, fish and other river creatures are periodically washed into the lake, which may be that the nearby rivers flooded the banks.

McCurry and Frese suspect that iron in nearby basalt sediments is dissolved in water passing through weathered rocks. This iron-containing water then reaches the groundwater level and finally seeps into rivers and lakes from the side.

Whenever fresh water with high oxygen content enters the lake-perhaps through heavy rain or flood-iron ions can no longer remain dissolved and quickly form goethite at the bottom of the lake. These rapidly precipitated minerals will bury leaves or corpses that happen to sink to the bottom of the lake. Over time, goethite replaced the buried soft tissues, and their shapes were recorded in the fossils we see today.

The team has reason to believe that the circulation of goethite in the lake may be caused by seasonal monsoon. Up to now, most of the hundreds of flower fossils found in mcgrath Plain have died before flowering, which indicates that the burial process takes place at a fixed time of the year. The team also found many insect fossils. In the modern ecosystem, these insects only appear in spring and summer.

In order to test their ideas and analyze the discovered fossil treasures, researchers still have a lot of work to do. McCurry and Frese are trying to improve the estimation of the age of fossil sites, which may help researchers better understand how McGraths Flat changed from a tropical rain forest to a dry bush-a clue to how the rain forest responds to today's climate change.

This artificially colored scanning electron microscope image shows four kinds of nematodes of liver fluke. These spores and other spores can be used as a reference for dating fossil-bearing rocks. They help researchers determine the age of fossil sites: from11million years to16 million years. Source: Michael Freys

A window to the past and the future

In the early and middle Miocene, the level of carbon dioxide in the atmosphere was about 400 to 500ppm, which is similar to the estimation of future carbon dioxide level by human activities. There was also a continuous warming period in Miocene, such as the best period of Miocene climate from170,000 years ago to140,000 years ago, which may overlap with the time period recorded in mcgrath Ping.

Wang Bo, a paleontologist at the China Academy of Sciences, said, "These results may help to better understand the future changes in the rainforest ecosystem caused by man-made global warming." He didn't take part in the new research. "This paper shows that tropical biota have reached at least 37 degrees south latitude in Australia, but we don't know when they came, when they left, and what is the driving mechanism."

McCurry said that even if the research team looks for more fossils, researchers will be busy with the dazzling specimens they find. "We actually have ten years of work to do."

(Translator: Zhang Yiran)