Extremely well-preserved fossil sawfly sheds new light on the coevolution of insects and toxic plants

A team of Australian researchers have described a new species of now-extinct sawfly based on an extremely well-preserved fossil found in central New South Wales.

This fossilized sawfly, aged 11 to 16 million years and dating from the Miocene, was the first of its kind discovered in Australia and only the second discovery in the world. It was discovered by a team of paleontologists in 2018 who were exploring McGraths Flat, a fossil site in central New South Wales that has since yielded many more detailed fossils.

This research was published in the journal Systematic entomology.

Despite their name, sawflies are not flies, but a type of wasp, with spitfires being the most widely recognized group of sawfly species in Australia. They are called sawflies because they have a saw-shaped ovipositor that is used to lay eggs, and they could be confused with flies because they do not have a typical “wasp waist.”

With the approval of the Mudgee Local Aboriginal Land Council, the words Wiradjuri were used to name the newly described species of sawfly Baladi warru. “Baladi” means “saw” and “warru” means “wasp”. This name honors the traditional owners of the land on which the fossil was located.

Researchers from Australia’s national science agency CSIRO, the University of Canberra, the Australian Museum and the Queensland Museum analyzed the sawfly’s wing vein and other features preserved in the fossil and determined its taxonomic location (scientific name) within sawflies. This allowed them to describe it as a new species.

CSIRO research scientist Dr Juanita Rodriguez helped describe the new sawfly species.

“We examined the fossil and its morphology, then combined this information with molecular and morphological data from a large sample of current sawfly species. This helped us decipher the fossil’s location in the tree of life of the sawfly,” Dr. Rodriguez said.

“We used the age of the fossil and its location to establish that sawflies originated in the Cretaceous, about 100 million years ago, meaning their ancient ancestors lived in Gondwana. When that supercontinent split , sawflies eventually became distributed in Australia and South America.

“When we examined the fossil, we identified pollen grains on the sawfly’s head, which revealed that it had visited a flowering Quintinia plant. This helped our team trace the complex interactions between species in the palaeoenvironment of McGraths Flat.”

University of Canberra palaeontologist and CSIRO visiting scientist Dr Michael Frese, who discovered the fossil sawfly, said the discovery would help researchers track the evolution and distribution of sawflies.

“In particular, this discovery helped us understand the incredible ability of sawflies to feed on toxic plants,” Dr. Frese said.

“They eat the leaves of Myrtaceae – a family of woody plants that includes eucalyptus trees – because they have mouthparts with which they can separate toxic oils or a chemical detoxification system inside their gut when they feed on myrtaceae leaves. This allows the larvae, sometimes called spitfires, to use the oils as a defensive weapon.

“From a broader perspective, our work helps researchers make sense of their current distribution in Australia and the Americas. Although this particular species, Baladi warru, has been extinct for millions of years, it provides information on native pollinators so that we can understand their evolution and impact in the present.