A unique snapshot of the time when rainforests covered the arid Australian continent

We now know how old the sediments are and how well preserved the fossils are, but we have years of work to describe and name all the species we find.

Researchers have discovered unique remains in the Australian fossil record of the Miocene era (between 23 million to 5.3 million years old), according to what they reported in a new scientific study published in the journal "Science Advances" on January 7.

Paleontologists have discovered the fossil treasure - known as "Lagerstadt", which means "storage site" in German - in "New South Wales", Australia, in a very arid region; So much so that British geologist John Walter Gregory called it "Australia's dead heart" more than 100 years ago.

The site of these exceptional fossils is known as a Fossil deposit, Fossil Reservoir or Lagerstätte in German, and it is a sedimentary deposit containing exceptionally preserved unusual fossils, and sometimes also preserved soft tissues.

These formations may have resulted from the body being buried in an oxygen-free environment with minimal bacteria and thus delayed decomposition, as the exceptional fossils discovered - including spiders, small fish, and ancient bird feathers - are buried and reveal a unique snapshot of when the rainforests were covered. Mostly arid continent.

"This site gives us unprecedented insight into what these ecosystems look like," lead study author Matthew McCurry, a curator of paleontology at the Australian Museum, told Live Science in an email. "We now know how diverse these ecosystems are, the species that live in them and how those species interact."

Millions of years ago, this site was a lush rainforest ecosystem, and was home to diverse plant and animal species, and the "Lagerstadt" site was kept secret on private land to protect it from illegal fossil collectors, while scientists excavated the remains of plants and animals that lived there At a time between 16 million and 11 million years ago.

Fossil sediments

"Lagerstadt" is a famous example of fossil sediments that span across geological ages to between 16 million and 11 million years, from the era of modern precursors to the present.

Most of the previous Miocene finds discovered by other scientists in Australia were bones and teeth from larger animals, yet the new cache contains fossils of small, delicate creatures such as spiders and insects, as well as plants from the Miocene rainforest.

Picture of an extinct Australian rainforest

By examining the well-preserved fossils with scanning electron microscopes (SEM), the study's authors were able to visualize minute details; Such as individual cells and subcellular structures. Some of the images even revealed the animals' recent meals, such as fish, larvae, and partially digested dragonfly wing preserved inside the fish's stomachs. In other fossilized scenes, freshwater mussels cling to the fin of a fish, and pollen grains were attached to the bodies of insects.

Paleontologists first visited the site in 2017, after a farmer reported finding fossilized leaves in one of his fields. "We were pleased to discover that the site yields a much wider range of fossils, including the remains of insects, spiders and fish," McCurry said.

The area of ​​the rocky layer bearing fossils is between one thousand and two thousand square metres, and paleontologists have so far excavated just over 50 square metres, and a matrix of iron-rich rocks called goethites surrounded the fossils on top of the sandstone layer.

It is possible that the flora and fauna in the stagnant pond were covered with iron and other minerals after runoff from the nearby basalt cliffs drained into the pond, known in Australia as 'bilabong', which has been preserved in great detail.

According to the authors of the study, the analysis of the preserved papers indicates that the average temperature at that time was about 17 degrees Celsius, and now - after millions of years - researchers have begun assembling fossils together to build a picture of an extinct Australian rainforest.

The scientists found leaves from flowering plants, pollen, fungal spores, more than a dozen fish specimens, "a variety of fossilized insects and spiders" and feathers from a bird that was roughly the size of a modern bird.

"I find the most amazing spider fossils," McCurry said. So far, only 4 fossil spiders have been known from Australia, and researchers have so far found 13 spider fossils at the new site, their eyes and skin bearing other exciting details and cellular structures that store dye called melanosomes. Although the color is not preserved, scientists can compare the shape, size and stacking patterns of the fossil pigment with those of modern animals.

In doing so, paleontologists can often reconstruct colors and patterns in extinct species, study co-author Michael Freese, an associate professor of science at the University of Canberra in Australia, said in a statement.

"This is really just the beginning of work on the fossil site," McCurry said. "We now know the age of the sediments and how well preserved the fossils are, but we have years of work to describe and name all the species that we find."