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Unknown Insect Trapped in Amber for 35 Million Years Is Identified

An insect encased in amber, with accompanying micro-CT scans.
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Researchers from the Department of Zoology at the University of Granada have captured micro-computed tomography (micro-CT) images of an undescribed insect trapped in amber for over 35 million years, allowing researchers to identify its species. The findings are published in Scientific Reports.

Examining a mystery species

The international research collaboration led by the University of Granada has discovered and described the specimen as Calliarcys antiquus, a member of the Ephemeroptera order – also known as mayflies.

Professor Javier Alba-Tercedor, professor of zoology at the University of Granada and co-author of the study, used a technique known as micro-CT to obtain clear images of the insect, enabling it to be studied and described in detail.

What is micro-CT?

Micro-computed tomography (micro-CT) uses X-rays to produce 3D images. Similar to a CT scan in a hospital, micro-CT is on a much smaller scale with an increased resolution of around 0.5 microns. X-rays “illuminate” and capture images of the object. Computer software programs convert two-dimensional cross-sectional images into three-dimensional images.

Based on 3D microscopy, micro-CT allows the internal structures of small objects to be captured non-invasively i.e., no cross-sections or complex pre-treatments are required. This means the sample is left intact for further analysis.

The insect was found embedded in a piece of Baltic amber estimated to be between 35 and 47 million years of age. Amber is formed from fossilized resin, a sticky, viscous liquid that is produced by conifers and other plants in response to damage. Insects that became trapped in this resin millions of years ago can still be found today, highly preserved in this fossilized material that we know as amber.

“The conservation of the specimens trapped inside the amber is often excellent, and the transparency of the material that surrounds them enables them to be studied, under a microscope, in great detail,” Alba-Tercedor explained. “But, in other cases, the level of transparency is not good because the areas of opacity that form prevent certain details from being examined.”

A discovery millions of years in the making

When the researchers examined this specimen from the Baltic, they found it was completely transparent – however, the insect itself was more translucent. This included parts of the body that are essential for identifying the specimen’s species, such as the end of the abdomen and the genitalia. As this translucence hindered its identification, the researchers subsequently turned to micro-CT.

Alba-Tercedor used this technique to reconstruct the entire insect, including those areas otherwise impossible to observe due to the opacity of the amber, identifying it as belonging to the genus Calliarcys. With expert knowledge from researchers at the University of Łódź and the Institute of Entomology of the Czech Academy of Sciences, the study of the previously undescribed species of mayfly was then completed by comparing DNA analysis from extant species of the genus (i.e., a species from the Calliarcys genus that has survived to the present day).

“In short, it all started with the discovery of a beautiful insect preserved in amber, which attracted the attention of the expert eyes of a scientist. And this ultimately required the enthusiastic collaboration and detective work of five scientists based in research centers located in four countries, who, after applying the latest techniques, were finally able to name and describe an insect that has remained locked inside a drop of amber for millions of years,” Alba-Tercedor summarized.

Reference: Godunko RJ, Alba-Tercedor J, Grabowski M, Rewicz T, Staniczek AH. Cenozoic origins of the genus Calliarcys (Insecta, Ephemeroptera) revealed by Micro-CT, with DNA barcode gap analysis of Leptophlebiinae and Habrophlebiinae. Sci Rep. 2022;12(1):15228. doi: 10.1038/s41598-022-18234-4

This article is a rework of a press release issued by the University of Granada. Material has been edited for length and content.