New research takes getting "caught in the act” to a whole new level with a pair of flies frozen in the act of fornicating. The climax of their life came to an abrupt end when a glob of sticky amber engulfed them, only to be dug up, found, and photographed by curious humans millions of years later.

The discovery, along with other specimens preserved in amber, are some of the oldest known from southern Gondwana – an ancient supercontinent that existed some 180 million years ago before its "last gasp," breaking up into modern-day South America, Africa, Madagascar, India, Antarctica, and Australia. The trove of amber fossil finds includes the oldest known ants from the region, juvenile spiders, biting midges, ‘slender springtails’, liverwort, and moss species.

Finding the "fossiliferous ambers in Australia and eastern New Zealand is a dream come true for a palaeontologist in this country, as amber preserves fossils in exceptional 3D space, just as they died many millions of years ago. Many researchers consider amber to be a 'Holy Grail' in the discipline," said lead author Jeffrey Stilwell, an associate professor at Monash University, to IFLScience.

The team unearthed more than 5,800 amber pieces in the Macquarie Harbour Formation in Western Tasmania and Anglesea Coal Measures in Victoria, Australia. The amber dates back to around 53 million (early Eocene) and 41 million years ago (middle Eocene), respectively. 

"The diversity and exceptional preservation of the terrestrial organisms are a huge (and welcome!) surprise to me as a palaeontologist, as we now have our first definite glimpses of ancient subpolar greenhouse Earth ecosystems, when Australia and Antarctica were attached and situated much further south in higher latitudes," Stilwell said.

The preparation of the amber was a delicate process: the team soaked the samples of amber, rock, and other material in water for 2 to 7 days. When the rock became soft enough, the samples were manually broken apart by hand into smaller pieces, and separated with a dissecting needle. The remainder of the samples were gradually worked through four sets of sieves with tiny millimeter holes to remove the fine organic sediment. 

"Australia now has its first fossil record of several groups of animals, plants and microorganisms, which reveal that the modern terrestrial ecosystems are quite ancient and of great antiquity. For example, there has never been a fossil ant recorded in Australia before, but we can now state for the first time that ants have been a significant part of the Australian ecosystem since the late middle Eocene Epoch."

In the amber pieces from the Macquarie Harbour Formation, which ranged from deep translucent red to clear, the team spotted nematodes – the oldest record of this group in the Southern Hemisphere. In amber from the Anglesea Coal Measures, the team discovered a group of juvenile spiders clustered together, which likely occurred after hatching for safety reasons until their next molt. The fornicating flies preserved in clear, honey-colored amber are a rare example of "frozen behavior". All the fossil finds are described in the journal Scientific Reports. 

"Australia has finally joined the global amber palaeontology community, which is quite exciting, as all of our discoveries of amber are in situ, i.e. in place in the rock. Previous reports are amber pieces without significant inclusions of animals or plants, or pieces of amber as 'float' and out of place and not in the rocks," said Stilwell. "The new amber finds rank up there with the most significant ever discoveries in Australian palaeontology and science, in general."