Evrim Yazgin
Cosmos science journalist
An extremely well-preserved sawfly fossil dating to 11–16 million years ago has been found in central New South Wales.
The specimen is an extinct species described for the first time in the journal Systematic Entomology. It was discovered at McGraths Flat near the town of Gulgong, more than 200km northwest of Sydney.
McGraths Flat is a recently discovered fossil site which preserves an ancient ecosystem of a billabong (oxbow lake) surrounded by rainforest. It dates to the middle of the Miocene epoch (23–5.3 million years ago).
At the time, global temperatures were much higher than today and the Australian landmass was wetter. Much of the north of the continent was covered in rainforest.
Among the remains found at McGraths Flat are soft-bodied creatures normally absent from the fossil record such as a large trapdoor spider and midge larvae.
The newly described sawfly fossil was found at initial fieldwork at the site in 2018.
It is identified as a sawfly species and named Baladi warru in the new paper. Its name is derived from the language local indigenous Wiradjuri words. Baladi means “saw” and warru means “wasp”.
“We looked at the fossil and its morphology and then put this information together with molecular and morphological data from a wide sample of current sawfly species,” says first author Juanita Rodriguez, a research scientist at CSIRO. “This helped us decipher the fossil’s placement in the sawfly tree of life.”
Today, there are about 8,000 species of sawfly. Despite their name, they are not flies but a type of wasp.
Sawflies get their name from their saw-like ovipositor – an appendage used by females to cut into plants and lay their eggs.
The researchers were able to place B. warru in a lineage of sawflies which emerged 100 million years ago in the Cretaceous period in the shadow of dinosaurs on the ancient supercontinent Gondwana.
“When this supercontinent split up, sawflies ended up distributed in Australia and South America,” Rodriguez explains.
The fossil also gives tantalising clues about how the prehistoric sawfly interacted with other organisms, and how characteristic traits of sawflies today have ancient roots.
“When we examined the fossil, we identified pollen grains on the sawfly’s head which revealed it had visited a flowering Quintinia plant,” Rodriguez says. “This helped our team trace complex species interactions in the palaeoenvironment of McGraths Flat.”
“In particular, this find has helped us in understanding the incredible ability of sawflies to feed on toxic plants,” adds co-author Michael Frese, a palaeontologist from the University of Canberra and visiting research scientist at CSIRO.
“They eat the leaves of myrtaceae – a family of woody plants that includes eucalypts – because they have mouthparts with which they can separate toxic oils or a chemical detoxification system inside their gut when feeding on myrtaceous leaves. This enables the larvae, sometimes called spitfires, to use the oils as a defensive weapon.
“In terms of the bigger picture, our work is helping researchers make sense of their current distribution across Australia and the Americas.
“Although this particular species, Baladi warru, has been extinct for millions of years, it provides information on native pollinators so we can understand their evolution and impact in the present.”
