New fossil find pushes back evidence of insect pollination to a time when pterodactyls still roamed the skies

Here is an artist’s impression of A. burmitina feeding on eudicot flowers. Credit: Illustration by Ding-hau Yang

A new study co-led by researchers in the United States and China has pushed back the earliest known physical evidence of insect flower pollination to 99 million years ago, in the middle of theCretaceous period.

The revelation is based on a flower beetle with pollen on its legs discovered preserved in amber deep in a mine in northern Myanmar. The fossil comes from the same amber deposit as the first ammonite discovered in amber, which was reported by the same research group earlier this year.

The report of the new fossil was published today (November 11, 2019) in the journal of the Proceedings of the National Academy of Sciences. The fossil, which contains both the beetle and the pollen grains, pushes the first documented example of insect pollination back to a time when pterodactyls still roamed the skies – about 50 million years earlier than previously thought. thought so before.

A. burmitina in amber

It’s A. burmitina in amber. The 99-million-year-old fossil, recovered from a mine in northern Myanmar, also contains 62 pollen grains from a eudicot flower. This is the earliest known physical evidence of insect pollination. Credit: Nanjing Institute of Geology and Paleontology

The US co-author of the study is David Dilcher, a professor emeritus in the Department of Earth and Atmospheric Sciences at IU Bloomington College of Arts and Sciences and a researcher affiliated with the Indiana Geological and Water Survey. As a paleobotanist studying the first flowering plants on Earth, Dilcher conducted research on the fossilization process of amber.

The study’s co-lead author is Bo Wang, an amber fossil expert at the Nanjing Institute of Geology and Paleontology, where the specimen was purchased and analyzed.

According to Dilcher, who provided a morphological examination of the 62 pollen grains in amber, the shape and structure of the pollen show that it evolved to spread through contact with insects. These characteristics include pollen size, “ornamentation”, and clumping ability.

The grains also likely come from a flower species in the eudicot group, one of the most common types of flowering plant species, he said.

A. burmitina in Amber (close-up)

Here is a close-up of A. burmitina in amber. The fossil also contains 62 pollen grains from a eudicot flower, indicating the insect’s role as a pollinator. Credit: Nanjing Institute of Geology and Paleontology

Pollen was not easy to find. The powdery substance was revealed hidden in the insect’s body hair under confocal laser microscopy. The analysis took advantage of the fact that pollen grains glow under fluorescent light, contrasting sharply with the darkness of the insect’s shell.

The insect in the amber is a recently discovered species of beetle, which the study authors named Angimordella burmitina. Its role as a pollinator has been determined based on several specialized physical structures, including body shape and pollen-feeding mouthparts. These structures were revealed by an imaging method called X-ray microcomputer tomography, or micro-CT.

“It’s extremely rare to find a specimen where the insect and the pollen are preserved in a single fossil,” Dilcher said. “Besides the importance as the earliest known direct evidence of insect pollination of flowering plants, this specimen perfectly illustrates the cooperative evolution of plants and animals during this period, during which a true exhibit of flowering plants has occurred.”

Prior to this study, the earliest physical evidence for insect pollination of flowering plants came from the Middle Eocene. The age of the new fossil was determined based on the age of other known fossils in the same location as the discovery of the fossilized beetle.

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Reference: “Pollination of Cretaceous flowers” ​​by Tong Bao, Bo Wang, Jianguo Li and David Dilcher, November 11, 2019, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.1916186116

The other study authors were Tong Bao and Jianguo Li from the Nanjing Institute of Geology and Paleontology. Boa is also affiliated with the Institute of Geosciences and Meteorology at the University of Bonn in Germany.

This work was supported in part by the Chinese Academy of Sciences and the National Natural Science Foundation of China.