50 million-year-old fossil assassin bug has unusually well-preserved genitalia

January 19, 2021

CHAMPAIGN, Ill. -- The fossilized insect is tiny and its genital capsule, called a pygophore, is roughly the length of a grain of rice. It is remarkable, scientists say, because the bug's physical characteristics - from the bold banding pattern on its legs to the internal features of its genitalia - are clearly visible and well-preserved. Recovered from the Green River Formation in present-day Colorado, the fossil represents a new genus and species of predatory insects known as assassin bugs.

The find is reported in the journal Papers in Palaeontology.

Discovered in 2006 by breaking open a slab of rock, the fossilized bug split almost perfectly from head to abdomen. The fracture also cracked the pygophore in two. A fossil dealer later sold each half to a different collector, and the researchers tracked them down and reunited them for this study.

Being able to see a bug's genitalia is very helpful when trying to determine a fossil insect's place in its family tree, said Sam Heads , a paleontologist at the Illinois Natural History Survey and self-described fossil insect-genitalia expert who led the research with Daniel Swanson, a graduate student in entomology at the University of Illinois Urbana-Champaign.

Species are often defined by their ability to successfully mate with one another, and small differences in genitalia can lead to sexual incompatibilities that, over time, may result in the rise of new species, Swanson said. This makes the genitalia a good place to focus to determine an insect species.

But such structures are often obscured in compression fossils like those from the Green River Formation.

"To see these fine structures in the internal genitalia is a rare treat," Swanson said. "Normally, we only get this level of detail in species that are living today."

The structures visible within the pygophore include the basal plate, a hardened, stirrup-shaped structure that supports the phallus, he said. The fossil also preserved the contours of the phallotheca, a pouch into which the phallus can be withdrawn.

The find suggests that the banded assassin bugs, a group to which the new specimen is thought to belong, are about 25 million years older than previously thought, Swanson said.

"There are about 7,000 species of assassin bug described, but only about 50 fossils of these bugs are known," he said. "This just speaks to the improbability of even having a fossil, let alone one of this age, that offers this much information."

This is not the oldest fossil bug genitalia ever discovered, however.

"The oldest known arthropod genitalia are from a type of bug known as a harvestman that is 400-412 million years old, from the Rhynie Chert of Scotland," Heads said. "And there are also numerous fossil insects in amber as old as the Cretaceous Period with genitalia preserved.

"However, it is almost unheard of for internal male genitalia to be preserved in carbonaceous compressions like ours," he said.

The researchers named the new assassin bug Aphelicophontes danjuddi. The species name comes from one of the fossil collectors, Dan Judd, who donated his half of the specimen to the INHS for study.
-end-
The INHS is a division of the Prairie Research Institute at the U. of I.

The National Science Foundation supported this work.

Editor's notes:

To reach Sam Heads, email swheads@illinois.edu. To reach Daniel Swanson, email drswanny@gmail.com.

The paper "A new remarkably preserved fossil assassin bug (Insecta, Heteroptera, Reduviidae) from the Eocene Green River Formation of Colorado" is available from the U. of I. News Bureau.

University of Illinois at Urbana-Champaign, News Bureau

Related Fossil Articles from Brightsurf:

Fossil shark turns in to mystery pterosaur
Lead author of the project, University of Portsmouth PhD student Roy Smith, discovered the mystery creature amongst fossil collections housed in the Sedgwick Museum of Cambridge and the Booth Museum at Brighton that were assembled when phosphate mining was at its peak in the English Fens between 1851 and 1900.

New fossil seal species rewrites history
An international team of biologists, led by Monash University, has discovered a new species of extinct monk seal from the Southern Hemisphere -- describing it as the biggest breakthrough in seal evolution in 70 years.

How to fix the movement for fossil fuel divestment
Bankers and environmentalists alike are increasingly calling for capital markets to play a bigger role in the war on carbon.

New fossil ape is discovered in India
A 13-million-year-old fossil unearthed in northern India comes from a newly discovered ape, the earliest known ancestor of the modern-day gibbon.

Fossil growth reveals insights into the climate
Panthasaurus maleriensis is an ancestor of today's amphibians and has been considered the most puzzling representative of the Metoposauridae.

Australian fossil reveals new plant species
Fresh examination of an Australian fossil -- believed to be among the earliest plants on Earth -- has revealed evidence of a new plant species that existed in Australia more than 359 Million years ago.

Tracking fossil fuel emissions with carbon-14
Researchers from NOAA and the University of Colorado have devised a breakthrough method for estimating national emissions of carbon dioxide from fossil fuels using ambient air samples and a well-known isotope of carbon that scientists have relied on for decades to date archaeological sites.

Rare lizard fossil preserved in amber
The tiny forefoot of a lizard of the genus Anolis was trapped in amber about 15 to 20 million years ago.

Reconstructing the diet of fossil vertebrates
Paleodietary studies of the fossil record are impeded by a lack of reliable and unequivocal tracers.

Fossil is the oldest-known scorpion
Scientists studying fossils collected 35 years ago have identified them as the oldest-known scorpion species, a prehistoric animal from about 437 million years ago.

Read More: Fossil News and Fossil Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.