DIGEST

Fossil trove sheds light on ancient antipodean ecology.

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An international team of palaeontologists has discovered an assortment of intact amber fossils in Australia and New Zealand that date from the mid-paleogene to the Late Triassic, 230 to 40 million years ago, reporting their find in the journal Scientific Reports.

The discovery includes southern Gondwana’s earliest fossil record of diverse groups of animals, plants and microorganisms, according to first author Jeffrey Stilwell from Monash University, Melbourne, and showcases the antiquity of modern life on Earth.

It gives us “our first definitive glimpses of ancient subpolar greenhouse Earth ecosystems, when Australia and Antarctica were attached and situated much further south in higher latitudes”, he says.

Among the relics are the first Australian fossils of slender springtails – a tiny, wingless hexapod – a cluster of juvenile spiders, biting midges (Ceratopogonidae) and the oldest known fossilised ants from this region.

“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,” says Stilwell, “when Australia was still attached to Antarctica during the last gasp of the Gondwana supercontinent.”

A notable rarity is two flies (Dolichopodidae) frozen while mating. “You could say these long-legged flies were caught in the act 42-40 million years ago, which is astounding for palaeontology in this country.”

Preserved non-vascular plants include two species each of moss, from Racopilum (Racopilaceae) and liverworts, Radula (Radulaceae).

Altogether, the team studied more than 5800 fragments of amber, an ancient tree resin that has preserved life from millions of years ago in exquisite 3D detail, fine enough to enable comparisons with modern species and gain evolutionary insights.

They sourced specimens from the Late Triassic and Paleogene in Tasmania, Late Cretaceous from Gippsland Basin in Victoria, Paleocene and late middle Eocene in Victoria and Late Cretaceous in the Chatham Islands, in New Zealand.

Until now, the oldest animals discovered in amber date back to the Late Triassic in the Dolomites of Northern Italy. Finding 230 million-year-old amber in Australia (Tasmania) points to extensive rainfall at that time.

This confirms that a major climatic shift, known as the Carnian Pluvial Episode, occurred across the whole Pangean supercontinent before it split into Laurasia and Gondwana around 200 million years ago.

As well as offering new insights into the ecology and evolution of southern Gondwana, the discovery is a boon for palaeontologists, opening up new avenues for future exploration, says Stilwell.

“Our findings provide exciting new insights into the origin, antiquity and evolution of the modern Australian biota and show that there may be a vast potential for future, similar finds in Australia and New Zealand.”