Beetle in the Coconut: Fossil Discovery Sheds New Light on Neotropical Rainforests

UNIVERSITY PARK, Pennsylvania – Tiny beetles that feed on fruits of the palm family may have developed their taste for coconuts a long time ago, according to a Penn State-led team of scientists studying the suspected insect damage in a 60 million year old fossil. .

“We found this remarkable fossil coconut that shows clear signs of insect tunneling,” said L. Alejandro Giraldo, a graduate geoscience student at Penn State. “After studying the damage in detail, we were able to identify the culprit insect: a group of beetles commonly known as palm bruchineas that today still eat a lot of palm fruit, including coconuts.”

The finds represent the first fossil evidence of beetles feeding on palm fruits and shed new light on the Neotropical rainforests that emerged in modern South America after the Cretaceous-Paleogene extinction event 66 million years ago. years that wiped out the dinosaurs and reshaped life on Earth. , the scientists said.

“These are the first neotropical forests as we know them today,” said Giraldo, whose adviser is Peter Wilf, a geosciences professor at Penn State. “We know that these forests had plants similar to those of today, and the next step is to find out what was happening to these forests – for example, how the insects interacted with the plants.”

Previous studies have focused on insect damage to fossil leaves, the most abundant plant parts found in the fossil record, the scientists said. Examples of insect damage to fruits and seeds are less common, but scientists have found six suspected insect holes on a coconut fossil from a site in modern Colombia.

The fossil contained damage to the outer and inner layers of the fruit, revealing a three-dimensional path that suggests the holes had a biological origin – like larvae worming their way through the coconut, the scientists said.

The team analyzed the number, position and size of the holes and scar tissue left behind and compared them to the damage caused by modern insects, particularly those that feed on plants in the palm family. The damage was consistent with a subgroup of modern beetles called palm bruchines, the scientists reported in the journal Review of Palaeobotany and Palynology.

“There are thousands of different insect species that can feed on seeds, but few of them feed on palm seeds, so that was the way to start,” Giraldo said. “After that he did a lot of detective work, really digging into the literature and studying different morphological characteristics in terms of how this damage occurs. And it paid off.”

This type of relationship between specific plants and insects – called specialized interactions – plays an important role in creating and maintaining plant diversity in modern Neotropical rainforests. By eating and destroying seeds, these highly specialized insects help prevent one group of plants from dominating the landscape.

The findings suggest that palm bruchines have been eating palm fruit regularly for at least 60 million years and that the specialized interactions that define modern Neotropical rainforests have occurred through geologic time, the scientists said.

“It’s something we see 60 million years ago, and it’s something that’s still happening today,” Giraldo said. “Our contribution is that we identify this specific group of insects as the culprit, and this group still lives today and attacks the same coconuts and palm trees as in the past.”

Mónica Carvalho, postdoctoral fellow at the Smithsonian Tropical Research Institute and former graduate student at Penn State, Fabiany Herrera, assistant curator of paleobotany at the Field Museum of Natural History in Chicago, and Conrad Labandeira, senior research geologist also contributed to this research. and Curator of Arthropod Fossils at the Smithsonian Institution.

The National Science Foundation funded this work.