In 2006 in the Green River Formation in Colorado, a rock slab broke. Looking at the pieces, they found a very well-preserved fossilized insect cut just in half. Later, a fossil dealer sold the two halves separately. Scientists at the University of Illinois (USA) realized its worth, so they put the pieces together to analyze it. Now they have found out that it is a new species and genus of assassin bug with a peculiarity. it preserves its genital organ almost intact.
Assassin insects, of the Reduviidae family, currently make up about 7,000 species of insects, such as bed bugs. From the order of Heteroptera, they are characterized by a thin neck-like structure that connects the narrow head to the body. They are called “assassins” because they use their short beak to pierce their prey and then suck the bodily fluids of their victims. However, although today we have many examples, there are barely fifty fossils discovered, so the newly baptized Aphelicophontes dan Judi in honor of Dan Judd, one of the collectors who owned one of the halves and donated it to the university for the study is a unique piece. And for various reasons.
The fossilized insect, which was trapped in the rock about 55 million years ago – in the Eocene – is about 4.5 centimeters. In it, the grating pattern of its legs can still be seen, although what most attracted the attention of the researchers was its well-preserved genital capsule, called pyrophorus, which is approximately the length of a grain of rice.
Being able to see the genitalia of an insect is very helpful when it comes to determining the place of a fossil insect in its family tree, says Sam Heads, a paleontologist with the Illinois Natural History Survey and leader of the research along with Daniel Swanson, a graduate student in entomology at the University of Illinois Urbana-Champaign. Together they have just published their results in the magazine.
As Swanson explains, Species are often defined by their ability to successfully mate with each other, and small differences in genitalia can lead to sexual incompatibilities that, over time, can result in the emergence of new species. This makes the genitalia a good place to thoroughly investigate and determine an insect species.
Such structures are often hidden in fossils like those in the Green River Formation, but not in such good condition. Normally, we only get this level of detail in species that are still alive. Visible structures within this insect’s pyrophore include the basal plate and another hardened, stirrup-shaped part that supports the phallus. The fossil also preserved the contours of the phyllosoma, a pocket in which insects can remove the phallus.
But these are not the oldest fossil insect genitalia ever discovered. There is a fossil that is between 400 and 412 million years old, from the Rhynie Chert site in Scotland, says Heads. And there are also numerous fossil insects in amber as old as the Cretaceous Period with preserved genitalia. However, it is almost unheard of for internal male genitalia to be preserved in carbonaceous compressions like the ones we have found in this specimen.
