First Mesozoic amber deposit with preserved insects discovered in South America

A scientific team has discovered the first Mesozoic amber deposit with preserved insects in South America in the province of Napo (Ecuador). The discovery, published in the journal Communications Earth & Environment, reveals that 112 million years ago there was a tropical rainforest with ferns, cycads and angiosperm plants, and describes a unique scenario for understanding the rich biodiversity and Cretaceous ecosystems in the southern hemisphere, little studied so far in the fossil amber record.

“This is the largest Mesozoic amber deposit in South America and one of the richest in Gondwana with bioinclusions. It is part of a recently discovered deposit in the Hollín Formation — detrital sedimentary rock levels of the Oriente Basin in Ecuador — and is dated to the Albian stage of the Lower Cretaceous, with well-preserved terrestrial arthropod remains (insects and spider web remains)”, says Professor Xavier Delclòs, from the Faculty of Earth Sciences and the Biodiversity Research Institute of the University of Barcelona (IRBio) and first author of the article.

The amber comes from a fluvial-lacustrine environment at the Genoveva quarry site (in the Tena region of the Amazon region). The resin-producing trees were probably araucariaceous conifers, according to geochemical and palynological analyses. “Everything indicates that the ancient ecosystem was wooded, humid and diverse, and has the oldest known association of angiosperm leaves in north-western South America,” says Delclòs, a member of the UB’s Department of Earth and Ocean Dynamics.

This study outlines a new framework for understanding equatorial ecosystems during the Cretaceous and the biogeographical relationships of their components when the modern continents broke away from the supercontinent Gondwana.

Teams from the Spanish Geological and Miner Institute National Center (IGME-CSIC), the Smithsonian Tropical Research Institute (Panama), the University of Rosario (Colombia), the Escuela Politécnica Nacional (Ecuador) and the Senckenberg Natural History Museum Frankfurt (Germany), among other institutions, have also participated in the study.
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Dense, damp forest with resin-producing trees

The study analysed 60 amber samples and identified 21 bioinclusions, with representatives of five insect orders, including Diptera (flies), Coleoptera (beetles) and Hymenoptera (ants and wasps), together with one spider web fragment. No plant remains were found within the amber, but a wide variety of plant fossils were identified in the rock samples, including spores, pollen and leaves.

The team has analysed samples of amber and surrounding rock from the Genoveva mine in Ecuador and identified two different types of amber: one formed underground around the roots of resin-producing plants (without inclusions) and another that formed when the resin was exposed in the air (with inclusions).

“This amber is chemically mature and altered by exposure to oil, as the Hollín Formation is an oil source rock, and is currently commercially exploited”, notes César Menor Salván, professor at the University of Alcalá.

The characteristics of the bioinclusions and surrounding fossils suggest that the amber formed in a dense, humid forest environment dominated by resin-producing trees.

 “Mostly chironomid and ceratopogonid dipterans were found, as well as springtails, coleoptera, hymenoptera, trichoptera, hemiptera and a fragment of a spider web. The insects point to the presence of freshwater bodies and a tropical rainforest in which the presence of rare families stands out, such as the wasps †Stigmaphronidae”, says Enrique Peñalver, researcher at the IGME in Valencia.

Carlos Jaramillo, from the Smithsonian Tropical Research Institute, says that “the pollen and macrofossils identified in the rocks that contained the amber reveal a forest with pteridophytes (ferns and related species), Araucariaceae and Cheirolepidaceae conifers, cycads and early angiosperms”, and adds that “epiphytic fungi have also been detected on the fossil leaves and resinicolous fungi”.

These characteristics contrast with the arid conditions observed in other South American deposits of the same age, such as the Crato Formation on the eastern margin of South America. In this case, no evidence of fire has been found, unlike many contemporary amber deposits in the northern hemisphere, probably due to the high humidity.

Experts stress that the discovery of this amber deposit is of great scientific relevance for future studies of this period. “Future excavations could help connect South American biodiversity with other regions of Gondwana, such as Antarctica, Australia and South Africa, where Cretaceous amber has also been found,” concludes Monica Solórzano Kraemer, from the Senckenberg Natural History Museum.