About 230 million years ago a Silesaurus opolensis was hungry. The close dinosaur relative, which stood as tall as a Great Dane and had a meter-long tail, foraged for food in the swampy vegetation of what is now southwestern Poland. Then, like all vertebrates, the reptile pooped out what it could not absorb. Millennia passed, and the waste petrified—along with several minuscule beetles embedded within it. These beetles, ambassadors of a long-lost lineage, now represent the first ever insect species described from a piece of fossilised excrement. The finding was reported on Wednesday in Current Biology.
Historically, amber has been the best source for paleontologists and entomologists to study ancient arthropods in three dimensions. Suspended in fossilised dollops of golden tree resin, these ants, spiders and beetles look like they could have been crawling around just moments ago. Apart from some preserved flies and mites, the oldest such fossils only date back to about 130 million years ago, leaving squashed flat specimens embedded in rock to document beetles from the earlier Jurassic and Triassic periods. But dung fossils, called coprolites, are an “abundant and overlooked” source of ancient information, says Martin Qvarnström, a paleontologist at Sweden’s Uppsala University and lead author of the new study. Not only can they reveal species or evolutionary insights, he says, but they also give paleontologists concrete evidence about the source animals’ ecosystems and diets.
Qvarnström and his colleagues uncovered a particular dime-size coprolite in a clay pit near Ozimek, Poland. The scientists were interested in the Triassic food web that Silesaurus was a part of, so they looked inside the opaque fossil with a technology called synchrotron microtomography. This process shot x-ray beams from all sides at the fossil to reveal its contents in stark relief. Digitally stitching the resulting image files together into a 3-D model of the coprolite’s interior was painstaking—“it’s similar to working in Photoshop,” Qvarnström says. But when the details of several beetles appeared, he was amazed. “It’s like they’re becoming alive in front of you,” he says.
To identify the insects, which were likely swallowed by the Silesaurus, the paleontologists contacted entomologist Martin Fikáček of Tawain’s National Sun Yat-sen University. Fikáček was initially skeptical that the beetles would be well preserved. “There are many fossils which look magnificent, but you cannot really say what [the specimen] is because you cannot see all the characteristics,” he explains. But Fikáček soon realised this specimen—with its clear variations in traits, such as its spindly antennae and segmented abdomen—set it apart from previously described beetles. “Step by step, we rechecked and double checked, did the computer analysis..., and it always confirmed that it’s an extinct lineage, something that is not surviving today.” The team named the new species Triamyxa coprolithica, in honor of its provenance.
“I’m really impressed with all they were able to do with these tiny things hidden away in coprolites,” says Margaret Thayer, a curator emeritus at the Field Museum in Chicago, who was not involved in the discovery. “This shows that coprolites can provide amazing specimens for study.” Researchers had imaged a few other coprolites in recent years. Some of them contained bits and pieces of insect, but none revealed a new species.
Synchrotron microtomography lets researchers see a “tremendous amount of detail” without ever laying eyes on the actual insect, Thayer says. “It just keeps amazing me that nobody has ever actually seen the physical beetle.” The high-resolution imaging technique “really revolutionised our ability to study a lot of previously completely recalcitrant specimens” such as T. coprolithica, she adds, noting that before it became available, “we wouldn’t even know they were specimens.”
T. coprolithica belongs to Myxophaga, a set of beetles that today live in large groups in wet, alga-blanketed environments. It is likely that the newly identified species lived in similar niches, and Fikáček is excited to see how such an old specimen is so much like currently existing members of the Myxophaga group. “It’s already tiny. It’s already living in masses—otherwise there’s no way the coprolite could be full of it,” he says. “They probably lived the same way they do today 230 million years ago. It’s like, wow, they are super ancient and had some super successful strategies to survive.” Of course, T. coprolithica did not make it to the present day. The reason it died out is unknown, but “in some ways, evolution is a big experiment,” Thayer says. “Some things work, and some things don’t.”
Both Qvarnström and Fikáček say more secrets to insect evolution might wait within the many poop fossils paleontologists have already found that date to the Triassic period and earlier. They hope the discovery inspires others to use imaging to peek inside these fossils and any future unearthed excrement. Dung that fossilises, against all odds, is likely to hide new clues about these ancient ecosystems, Qvarnström adds. “Go out there and look at more coprolites!” he says.