Waters of the deep past: the fossil aquatic insects of New South Wales

Insects are fragile creatures with little chance to fossilise. Where shells and bones weather the passage of time, insects crumble. But the New South Wales outback holds an amazing, and exceptional, treasure.

While working at the Australian Museum during my Visiting Collections Fellowship, I had the privilege to work with not one, but two treasure troves of fossil aquatic insects. In February and March 2020, I worked alongside the palaeontology department of Australian Museum on some of the most outstanding insect fossils in the world. In the past, I have visited Australia to work on the pupae of non-biting midges (Chironomidae) from the Jurassic Talbragar fish beds. So, I set out to work on these fascinating fossils, which soon will be described as a new genus of midges.

While working on these pupae, Curator of Palaeontology at the Australian Museum, Dr. Matthew McCurry, introduced me to even more fascinating collections of aquatic insects. Matthew kindly invited me to participate in the excavation and examination of the McGraths Flat Lagerstätte (a high fossil-yield preservation site), which was recently published and made quite a splash both nationally and internationally.

McGraths Flat is an 11 to 16 million years old fossil deposit from the Miocene epoch, which preserves thousands of plants and animals. Miniscule details of animals and plants, including at the cellular level, were conserved in the iron-rich rock matrix. McGraths Flat is particularly rich in insect fossils, with aquatic insects being most abundant.

The abundance of aquatic insects at McGraths Flat was very exciting to me because these animals can be studied as indicators of the conditions in the environment. Thus, I can use them to learn more about the past environment and ecological connections of McGraths Flat. The best example is an abundance of phantom midges’ larvae (Chaoboridae) at the site. There are thousands of specimens of these midges at this site, and since these larvae normally need calm aquatic conditions with few predators (such as fishes) to survive, it is a safe bet that the McGraths Flat fossils were put to rest in a slow flowing or standing body of water, such as a billabong.

As the formal description of the new deposit has now been published, I am now working with colleagues from the Australian Museum and the University of Canberra to describe all the new species of aquatic insects we found. We have at least two new species of mayflies, two new species of dragonflies, one new species of alderfly, one new species of caddisfly and at least four new species of fly. One fossil especially dear to my heart, which I am looking forward to describing, is a new genus of Cranefly (Limoniidae) which I found myself during the dig.

Fossil aquatic insects of NSW tell us fascinating stories about the aquatic past of Australia. My research into the topic will allow us to better understand how climate change impacted Australian freshwaters in the past, and what future their might be.

Dr Viktor Baranov, Postdoctoral researcher, Ludwig Maximilian University of Munich, Germany; 2019/20 AMF/AMRI Visiting Collections Fellow, Australian Museum