A rare fossilized assassin is causing a bit of a stir in entomological circles because it is so remarkably well preserved that you can clearly see his penis. The specimen dates back to 50 million years in the Eocene, meaning this particular taxonomic group may be twice as old as scientists previously believed. The University of Illinois, Urbana-Champaign (UIUC) researchers who conducted the analysis described their unusual find in a new paper published in the journal Papers in Palaeontology.
“It’s really rare to get a fully fossilized insect, but it’s pretty amazing and exciting to get a fossil of an insect from so long ago that has so much detail,” Gwen Pearson of Purdue University’s Department of Entomology, who is not a co-author on the paper, told Ars. Assassin bugs (part of the Reduviidae family, of the order hemiptera) are predators favored by gardeners because they eat pests. The mouth is clearly shaped like a straw, all the better for poking into the body of its prey, like a juice box, and slurping the entrails out.
But, of course, it’s the preserved genitalia that make this fossilized specimen so exciting. The genitals are in a sheath — Ruth Schuster, writing in Haaretz, described the assassin’s penis (technically its “pygophore”) as a “chitinous codpiece” — therefore it’s hard to tell whether a particular insect specimen is male or female. . In addition to the pygophore and telltale stripes on the legs, the new fossil also clearly shows the “basal plate,” a stirrup-shaped structure that supports the penis.
“What makes insect penises so interesting is that in many cases they are part of the exoskeleton,” Pearson said. “It’s not because entomologists are perverted, it’s because genitals are where we can watch evolution happen. That’s where sexual selection is strongest. And the more we know about how insects lived and diversified in the past, that helps us understand how they live and diversify now.”
Among other rare ancient insect finds is the 2013 discovery of a fossilized pair of insects in a related taxonomic group known as Froghoppers (Anthoscytina perpetua), caught in flagrant crime, their copulation has been preserved in detail for more than 165 million years. The froghoppers were so well preserved in a belly-to-belly mating position that the male can be seen inserting his “aedeagus” (analogous to the penis) into the female’s “bursa copulatrix”.
Most insect fossils are found in several dozen ‘jackpot’ deposits known as Konzentrat Lagerstatten, roughly translated as “a repository where a whole host of fossils were kept,” according to a new Entomology Today article. Those fossil-rich regions include the Green River Formation, a series of sedimentary deposits in what is now Colorado, Utah and Wyoming. That’s where this new fossil was found in 2006, near Meeker in Colorado’s Rio Blanco County, by a fossil collector named Dan Judd. The old bug has been dubbed Aphelicophontes danjuddic in his honor.
Another unusual feature is that the specimen split neatly in two in the field when Judd found it, rather than one half enveloping the actual fossil and the other capturing the impression, which is what usually happens. “Green River shales are very well laminated and split nicely like the pages of a book,” study co-author Sam W. Heads, a paleontologist at UIUC, told Ars. “I expect Mr Judd gave the stone a few taps with a hammer and flipped it open, revealing the specimen inside. It was pure luck that it split through the coronal plane like that. small preparation in the lab with a very fine pin mounted in a pin vise, just to remove some matrix covering certain parts of the body. Other than that the item was perfect.”
When Heads first received half of the specimen, “he was impressed by the beautiful preservation, including the beautifully preserved color pattern,” he said. “I immediately recognized it as a hit man and was simply ecstatic about them as they are not common in the fossil record. I ran straight to my colleague’s office next to mine to show him the specimen.”
Upon further examination under the microscope, he realized that the internal genitalia were also very well preserved – cause for even more excitement. “I didn’t get much sleep that night,” Heads admitted. Within a week, he learned that Judd was willing to donate his half of the specimen, which helped Heads and lead author Daniel Swanson, Heads’ graduate student, learn even more about the bug’s morphology. “I had another joyous moment when I examined it and found that the genitals were also visible on that half, and not only that, but it retained slightly different parts of the phallic complex,” he said. “I realized we might be able to reconstruct the phallus morphology of this insect.”
Much of the article focuses on tracking down the various minor details of this particular specimen in detail to substantiate the final species assignment. Heads and Swanson also soaked the butts — pardon, “caudal ends” — of a representative sample of modern assassins in water so they could easily remove the genitals with tweezers. When they compared those genitals to the fossilized sample, they matched. This provides “strong evidence that the genitalia were similar in the group and likely were under similar selection pressure over the past 50 million years,” the authors concluded.
According to Pearson, fossilized insects from millions of years ago, despite being around for so long, have the same basic body plan as their modern-day counterparts. “The Pieces That Change” [over the course of evolution] are the little squidgy bits,” she said. “So much of what we know about insects and how we classify them is about their genitals, because very often each species has different bits that only fit their species.”
Heads said this new fossil belongs to a branch of a family tree that is typically 25 million years old. Given that this fossil is 50 million years old, it’s possible that a branch of assassins diversified earlier than previously believed.
Swanson is now completing work for his doctorate, which includes compiling a detailed survey and catalog of all known fossil assassins, and correcting a few taxonomic errors made by other scientists in the past. According to Heads, one of the main potential implications of Aphelicophontes will be its use in calibrating molecular phylogenetic analyzes of the entire Reduviidae†
“This is like reconstructing the family history or genealogy of the group, determining how the different genera and species are related,” he said. “Fossils Like” Aphelicophontes are extremely valuable in this type of work because they provide us with a minimum age for a particular lineage, which provides estimates of divergence times and can provide important data on the acquisition of different morphological characters over time.”
In addition, “Aphelicophontes tells us something about the paleoecology of the ancient paleobiota of the Green River Formation,” Heads said. “Assassin bugs are important predators in terrestrial ecosystems, so it’s helpful to know they were there as part of the ancient insect fauna .”
DOI: Papers in Paleontology, 2021. 10.1002/spp2.1349 (About DOIs).