Prehistoric flies trapped in amber

There’s bad days, and then there’s this. Around 41 million years ago, two prehistoric flies on the southern tip of Gondwana were happily mating away when they found themselves in a sticky situation.

Unfortunately for the amorous pair of long-legged flies (Dolichopodidae), they found themselves stuck in the resin of a tree while getting frisky, unable to free themselves. Covered in sap, the two lovers have been frozen in time for 41 million years as it hardened to amber, entombing them inside.

The poor flies were just one sample of a treasure trove of 5800 amber samples found across the southeastern Australia and Tasmania. The collection of samples has been described in the journal Scientific Reports.

When the flies sample first crossed the desk of Jeffrey Stilwell, from Monash University, he couldn’t believe what he was seeing. While insects being trapped in amber is not unknown (it was the basis of Jurassic Park after all), he was not expecting to see two prehistoric flies rooting in their last moments.

But the story may not be all so romantic.

“It’s possible one fly was trapped in the amber and the other was a little excited and tried to mate,” says Victoria McCoy, a palaeontologist from the University of Wisconsin-Milwaukee, told The New York Times. McCoy was not involved in the current study. It probably serves it right then.

Frozen behaviour

To see two insects in action inside amber is referred to as “frozen behaviour”, and is extremely rare to find. As Stilwell describes, it means that absolutely nothing occurred between the flies behaving the way they were, dying, and being encased in sap.

“This may be the first example of ‘frozen behaviour’ in the fossil record of Australia,” says Stilwell.

Prehistoric flies_amber_flies
A large piece of amber with an association of two prehistoric flies (long-legged on left and biting midge on right) with the first ever Australian fossil of a large mite of the extant genus, Leptus, Anglesea, Victoria, ca. 41 million years old. Credit: Enrique Peñalver.

“Frozen behaviours are rarely recorded in the fossil record, but can be quite diverse, including defence, parasitism, feeding, swarms, and so on.”

The ruins of Pompeii are the closest example of human frozen behaviour, where city dwellers were entombed by the exploding Mt Vesuvius seemingly during whatever activity they happened to be doing.

Most of the amber samples that have been found, however, originate from the northern hemisphere. Relatively little has been found from the ancient southern supercontinents. Then, in 2011, Stilwell stumbled across amber samples in the south of Victoria, which spurred him to search for more.

In all, the amber samples discovered across southeastern Australia, Tasmania and New Zealand range from around 230 million years old to 40 million years old. This time period means the oldest amber samples were formed on the Pangea supercontinent during the Triassic period, while others formed after Pangea began breaking up and formed Gondwana. Gondwana, the supercontinent made up of South America, Africa, Madagascar, India, Antarctica, and Australia, broke away from the Pangea supercontinent around 200 million years ago.

The youngest samples date from the mid-Paleogene periods.

Fornicating flies just the start

Stilwell’s amber find include the oldest reported amber from Southern Pangea dating back to 230 million years ago, 96-92 million year old deposits from forests near the South Pole, and an intact fossil of an insect called a felt scale (Eriococcidae) from 54-52 million years ago.

From the Macquarie Harbour Formation in Western Tasmania, and Anglesea Coal Measures in Victoria, the team also found ants which lived in Southern Gondwana, the oldest ever found from that area. The fossilised ants are part of a group still alive today.

The first Australian fossils of ‘slender springtails’, a tiny, wingless hexapod, were also discovered. Other organisms preserved in the amber include a cluster of juvenile spiders, biting midges (Ceratopogonidae), two liverwort and two moss species.

Prehistoric flies_amber_biting midge
Flake of clear yellow amber from Anglesea, Victoria containing a new, beautifully preserved biting midge ca. 41 million years old. Credit: Enrique Peñalver.

As many of the amber samples were recovered from coal deposits, it’s a sign that the area was covered in plant life at the time. This includes trees producing sap that became the amber itself.

The samples have already provided new insights into the origin and evolution of species. But as the team analyse more amber samples, they hope to find never-before-seen species that lived on Gondwana.

The start of the amber story in Australia and New Zealand may just begin with rooting flies.

This article was first published on Australia’s Science Channel, the original news platform of The Royal Institution of Australia.

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