Unusually Protected Genitals in 50 Million-Year-Old Fossil Killer Insect

This fossil, which survived the formation of the Green Tea in present-day Colorado, represents a new species and range of predatory insects known as the killer beetle. The researchers called the sample Aphelicophontes danjuddi. A small insect was also fossilized with the sample. Credit: Image courtesy Paleontological Association

The fossilized insect is small, and the genital capsule, called the pygophore, is about the length of a grain of rice. Scientists say this is attractive because the insect’s physical features – from the bold band pattern on its legs to the internal features of the genitals – are clearly visible and well-preserved. The fossil that survived the formation of the Green Tea in present-day Colorado represents a new species and genus of predatory insects known as the killer beetle.

The find is reported in the journal Documents in paleontology.

Sam Heads

Illinois Natural History researcher paleontologist Sam Heads led the study of an extraordinarily well-preserved 50-million-year-old fossil beetle. Credit: Photo by Brian Stauffer

The fossil beetle, which was discovered in 2006 by breaking a rock floor, split almost completely from head to toe. The fracture also split the pygophore in two. A fossil vendor then sold each half to a different collection, and the researchers tracked them down and reassembled them for the job.

Sam Heads, a paleontologist at the Illinois Natural History Study and self-leading fossil insect sex expert who led the study with Daniel, is very helpful when trying to determine the location of a fossil insect in a family tree. Swanson is a graduate student in entomology at the University of Illinois at the University of Urbana-Champagne.

According to Swanson, species are often identified by their ability to successfully mate with each other, and small differences in the sex organs can lead to sexual incompatibilities that can result in the growth of new species over time. This makes the genitals a good focus for identifying an insect species.

However, such structures are often hidden in compression fossils, as in the Green River formation.

“It’s a rare treatment to see these delicate structures in the internal genitals,” Swanson said. “Normally we get this level only in species that live today.”

The structures visible inside the pygophore include the basal plate, a hardened, floating structure that supports the horoscope, he said. The fossil also preserves the contours of the phallus, a sac in which the phallus can be retracted.

Daniel Swanson

I. entomology graduate student Daniel Swanson led research on the fossil of an ancient killer beetle. Credit: Photo by Brian Stauffer

The discovery said that the killer insects, a group thought to belong to the new specimen, were about 25 million years older than previously thought.

“There are about 7,000 species of killer beetles described, but only 50 fossils of these insects are known,” he said. “It’s about the impossibility of owning such a fossil at this age, which is so informative.”

However, this is not the oldest fossil beetle genital organ ever found.

“The oldest known arthropod genus is from the Scottish Rhynie Chert, a species of insect known to be a reaper 400-412 million years old,” he said. “There are also a lot of fossils in the old amber Chalk The period is protected by the genitals.

“However, the protection of the internal male genitals in carbon compressions like ours is almost unheard of,” he said.

Researchers have named the new killer beetle Aphelicophontes danjuddi. The name of the species comes from Dan Judd, one of the fossil collectors who donated half of the sample to INHS for research.

Reference: January 19, 2021, Documents in paleontology.
DOI: 10.1002 / spp2.1349

INHS is a division of the Commonwealth Prairie Research Institute.

The National Science Foundation supported this work.

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