Palaeontology: South American amber deposit ‘abuzz’ with ancient insects

(Press-News.org) The first amber deposits in South America containing preserved insects have been discovered in a quarry in Ecuador, reports a paper in Communications Earth & Environment. The finding provides a snapshot of a 112-million-year-old forest on the supercontinent Gondwana, and presents new possibilities for studying a currently little-known ancient ecosystem.

Amber (fossilised tree resin) samples have a wide date range, with the earliest dated to 320 million years ago, but there is a notable increase in the number of samples in the fossil record between 120 million and 70 million years ago, during the Cretaceous era (143.1 million to 66 million years ago). Amber can contain bio-inclusions — ancient plant or animal matter preserved inside the resin — which give researchers an opportunity to study organisms, such as insects and flowers, that are otherwise rarely preserved. However, until recently, almost all major identified amber deposits have been located in the Northern Hemisphere. As such, we have a limited understanding of the biodiversity and ecosystem of the Southern Hemisphere during the Cretaceous era, when the modern continents were breaking away from the supercontinent Gondwana.

Xavier Delclòs and colleagues analysed samples of amber and the surrounding rock from the Genoveva quarry in Ecuador. The amber, dated to approximately 112 million years ago, is part of a recently discovered deposit in the Hollín Formation, a sedimentary rock layer lying across the Oriente Basin in Ecuador. The authors identified two different types of amber: one that formed underground around the roots of resin-producing plants, and another that formed when resin was exposed to air. In the 60 analysed samples of aerial amber, the authors identified 21 bio-inclusions, consisting of members of five insect orders — including Diptera (flies), Coleoptera (beetles), and Hymenoptera (which includes ants and wasps) — along with a fragment of spider web. They also identified a wide variety of plant fossils in the rock samples, including spores, pollen, and other remains.

The authors conclude that the characteristics of the bio-inclusions and surrounding fossils suggest that the amber formed in a humid and densely vegetated forest environment, dominated by resin-producing trees, and located in the southern part of Gondwana. They argue that the discovery of the amber deposit is of critical importance for future studies of this period.

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