Paleontologists have found insect borings in a fruit fossil of the genus Cocos (coconuts) from the Paleocene Cerrejón Formation of Colombia. Their findings represent the earliest fossil evidence of seed beetles feeding on palm fruit and shed new light on the Neotropical rainforests that emerged in modern day South America following the Cretaceous-Paleogene extinction event 66 million years ago.
Modern Neotropical rainforests are characterized by the high intensity and host specificity with which insects feed on plants.
Previous studies have shown that, during the Middle-Late Paleocene, the leaves of the early evolving rainforests in tropical South America were heavily herbivorized by insects.
Yet, less attention has been given to insect damage found on fossil fruits and seeds.
“These were the first Neotropical forests as we know them today,” said L. Alejandro Giraldo, a graduate student in the Department of Geosciences and Earth and Environmental Systems Institute at Pennsylvania State University and the Smithsonian Tropical Research Institute.
“We know these forests had similar plants compared to today, and the next step is knowing what was happening to these forests — for example how insects were interacting with the plants.”
Giraldo and colleagues found six suspected insect holes on a coconut fossil from the Cerrejón Formation in modern day Colombia.
The fossil contained damage to the outer and inner layers of the fruit, revealing a 3D path that suggests the holes had a biological origin — like from larvae eating their way through the coconut.
The paleontologists analyzed the number, position and size of the holes and the scar tissue left behind and compared that with damage caused by modern insects, especially those that feed on plants from the palm family.
The damage was consistent with a sub-group of modern beetles called palm bruchines.
“We found this remarkable fossil coconut that has clear signs of insect tunneling,” Giraldo.
“After studying the damage in detail, we were able to pinpoint the insect culprit: a group of beetles commonly referred to as palm bruchines that today still eat lots of palm fruit — coconuts included.”
The findings suggest that palm bruchines have consistently eaten palm fruits for at least 60 million years and that the specialized interactions that define modern-day Neotropical rainforests have occurred through geological time.
“This is something that we see 60 million years ago, and it’s something that is still occurring today,” Giraldo said.
“Our contribution is that we pinpoint this specific group of insects as the culprit, and that group is still living today and attacks the same coconuts and same palms as it did in the past.”
The team’s paper was published in the journal Review of Palaeobotany and Palynology.
L. Alejandro Giraldo et al. 2022. Ancient trouble in paradise: Seed beetle predation on coconuts from middle-late Paleocene rainforests of Colombia. Review of Palaeobotany and Palynology 300: 104630; doi: 10.1016/j.revpalbo.2022.104630
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