Last supper for prehistoric pollinating beetle

Identifying who pollinated flowers in prehistoric times might be as simple as looking at fossilised beetle poo.

A team of researchers, led by Erik Tihelka of the University of Bristol, UK, unearthed an amber fossil of a Cretaceous beetle, Pelretes vivificus, whose fossilised faeces was packed with pollen, suggesting that the beetle was a useful pollinator of flowering plants 98 million years ago.

Key research points

  • 98-million-year-old fossilised beetle ate pollen
  • The beetle may have been an important pollinator
  • Pollen diet shows coevolution with flowering plants

“The fossil faecal pellets are completely composed of pollen, the same type that is found in clusters surrounding the beetle and attached to its body,” says Tihelka, “We thus know that Pelretes visited angiosperms to feed on their pollen.

“This finding provides a direct link between early flowering plants in the Cretaceous and their insect visitors; it shows that these insect fossils were not just incidentally co-preserved with pollen, but that there was a genuine biological association between the two.”

Dorsal view of pelretes vivificus, a cretaceous short-winged flower beetle (kateretidae) from burmese amber (~99 ma). Scale bar: 200 μm.
A Cretaceous short-winged flower beetle from Burmese amber (~99 Ma). Scale bar: 200 μm. Credit: Chenyang Cai, Yanzhe Fu and Yitong Su

Insects that are fossilised in amber are preserved with such clarity that they give a lot of information about what it was like during the Cretaceous period, and how symbiotic relationships may have evolved.

“Luckily, the amber trap from northern Myanmar is one of the richest fossiliferous amber deposits known,” says Tihelka, “Besides the unparalleled abundance of fossil insects, the amber dates back to the mid-Cretaceous, right when angiosperms were taking off.”

While flowering plants dominate today, they only evolved about 125 million years ago. This 98-million-year-old fossil shows that the beetle may have quickly taken advantage of the pollen in early angiosperms, and this mutual relationship formed how both species evolved, the researchers suggest.

This could be seen in both the pollen content of the faeces and certain physical aspects of the beetle.

“The beetle is associated with clusters of pollen grains, suggesting that short-winged flower beetles visited angiosperms in the Cretaceous,” says Professor Chenyang Cai, palaeontologist from the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences (NIGPAS).

“Some aspects of the beetle’s anatomy, such as its hairy abdomen, are also adaptations associated with pollination.”

Today, the closest living relatives to this ancient beetle are the Australian short-winged flower beetles (Kateretidae family).

“The pollen associated with the beetle can be assigned to the fossil genus Tricolpopollenites,” explains Liqin Li, fossil pollen specialist from NIGPAS. “This group is attributed to the eudicots, a living group of angiosperms, that includes the orders Malpighiales and Ericales.”

The paper was published in Nature Plants.

Aggregations of eudicot pollen and pollen-containing coprolites associated with pelretes vivificus. A, amber piece with p. Vivificus, showing coprolites and one pollen aggregation. B-e, details of pollen under visible light (d) and confocal laser scanning microscopy
Aggregations of eudicot pollen and pollen-containing coprolites associated with Pelretes vivificus. (a) Amber piece with P. vivificus, showing coprolites and one pollen aggregation. (b-e) details of pollen under visible light (d) and confocal laser scanning microscopy (b, c, e). Scale bars: 1 mm (a), 50 μm in (b, e), 100 μm (c, d). Credit: Chenyang Cai, Yanzhe Fu and Yitong Su

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