The discovery of an exceptional new fossil site offers a glimpse into Australia’s ancient rainforests

Every fossil provides a glimpse into a past world with plants and animals that are often very different to those that we can see on today. Unfortunately, most fossils preserve only hard body parts like shells, bones, and teeth. This means that palaeontologists still have many questions about how organisms without hard parts looked like. Equally challenging is the reconstruction of soft tissues, even if bones or other hard parts have survived.

Luckily, there are some exceptions. A handful of fossil sites around the world preserve soft tissues of organisms. These sites are extremely important for studying how life has changed over time. They are so important that palaeontologists have a special term for them: “Konservat-Lagerstätten”.

Today we published an article documenting the discovery of one such Konservat-Lagerstätte in the international journal Science Advances. We named the new fossil site ‘McGraths Flat’ after Nigel McGrath who discovered the first fossils at the locality. McGraths Flat provides unprecedented insight into the time of the Miocene, approximately 15 million years ago, when rainforests covered most of Australia. The site, which is located in central NSW, is exceptional for a couple of reasons.

Firstly, the site contains a range of fragile and soft-bodied organisms that are normally missing from the fossil record. While hundreds of Miocene fossil sites preserve kangaroo bones throughout Australia, we have very few sites that preserve smaller more fragile animals, like insects or spiders. Normally, these organisms tend to decompose before they are covered by sediments and the process of fossilisation begins. For example, up until a few years ago when we started digging at McGraths Flat, only four fossil spiders had been found in the whole of Australia. At McGraths Flat, we have so far unearthed thirteen spiders, often completely preserved; even miniscule anatomical features are still visible. A multitude of insect groups are also preserved in stunning detail, which includes dragonfly nymphs, assassin bugs, cicadas and parasitoid wasps. Almost all of them represent species that are new to science and have not yet been named.

Secondly, the fossils that we find at the site are preserved with extremely high fidelity. Under a scanning electron microscope, we can see the structure of individual body cells and sometimes, even very small intracellular organelles such as melanosomes are preserved. In fish and birds, the number, shape and packaging of these tiny organelles is associated with certain colours. Thus, the fossils from McGraths Flat allow us to reconstruct the colour pattern of some Miocene animals.

Thirdly, the high-quality preservation allows us to find evidence for species interactions that or normally difficult to track down. For instance, we found pollen on the body of a sawfly, allowing us to tell which flower was visited and possibly pollinated before the insect died. In other instances, the diets of organisms can also be reconstructed. For example, we found several fossilised fish that still possess the remains of prey within their stomachs. An ancient example of parasitism is on display in another fossilised fish; closer inspection revealed a larval mussel attached to the tail fin. These young mussels are temporary parasitic. For a few weeks, they hitch a ride and feed on the slime that covers the skin of the fish. Though these larvae are common fossil finds, none has ever been preserved while affixed to its host. Discoveries such as these not only grant us the resources to learn more about past species interactions but reaffirm the extraordinary quality of the fossils from this newly discovered Konservat-Lagerstätte.

Finally, the site is significant, because it can tell us about how changes in the climate impacted ecosystems. Using pollen and spore grains preserved in the sediments at this fossil site, we were able to date the fossils to the Miocene epoch. During the Miocene, Australia changed dramatically. Once widespread rainforests were replaced by the deserts and shrublands that now dominate the landscape. There is some evidence in the fossils from McGraths Flat that the ecosystem was in a state of change. The pollen suggests that there might have been dryer habitats surrounding the rainforest, which indicates that rainforests in NSW might have already begun changing into dryer habitats at the time.

Over the coming years we plan to continue excavating the site to learn more about the Miocene environment and to use the information to better predict how modern Australian environments may respond to climate change.

Dr Matthew McCurry, Scientific Officer - Curator, Palaeontology, Australian Museum Research Institute.

Dr Michael Frese, Faculty of Science and Technology, University of Canberra; Commonwealth Scientific and Industrial Research Organisation; and Australian Museum Research Institute.

Ailie Mackenzie, MRes Candidate, Macquarie University and the Australian Museum.