Fossilized dung from a dinosaur ancestor yields a new beetle species

In a fossilized chunk of ancient reptilian poo, scientists have uncovered complete specimens of a new beetle species. The finding, described June 30 in Current Biology, suggests that fossilized dung could contain more details about past life than previously thought.

Such ancient feces have been “largely overlooked,” says evolutionary biologist Martin Qvarnström of Uppsala University in Sweden. “But they often contain very well-preserved fossils. They’re like hidden treasure chests.”

Fossilized dung, also known as coprolite, can reveal insights about the diets of extinct creatures that body fossils can’t. For example, coprolites have been used to show that some dinosaurs with plant-based diets also ate crustaceans (SN: 9/21/17).

Feces, especially from carnivores, can readily form into coprolites because the excrement often contains the raw materials and bacteria needed for mineralization, says paleontologist Karen Chin of the University of Colorado Boulder, who was not involved in the study. Laboratory experiments have shown that poo can become a coprolite in just weeks, saving any delicate structures within as the dung is buried over time. “If you didn’t get rapid mineralization, the feces would get flattened, but most coprolites are three-dimensional,” she says.

Despite this preservation power, coprolites can be overshadowed by amber, a translucent tree resin, when it comes to fossils. Some of the most well-preserved, three-dimensional insect fossils are found in amber. But since the resin became common only around 130 million years ago, amber-preserved insects older than that are rare.

Curious whether much older, fossilized poop could match the fossil quality of amber specimens, Qvarnström and colleagues used a synchrotron, which generates powerful X-rays, to peek inside a coprolite from Poland. The dung likely comes from an extinct dinosaur relative called Silesaurus opolensis, which lived around 237 million to 227 million years ago during the Triassic Period.

The synchrotron scan revealed whole beetle fossils that rival the quality of similar specimens in amber, along with fragments of the same kind of beetle. The whole beetles’ fossilized exoskeletons lacked the joints needed for classification, but by piecing together the fragmented beetles, the researchers were able to reconstruct these features. As a result, the team identified the insects as a new family and species of beetle, named Triamyxa coprolithica.

Qvarnström hopes more paleontologists will begin to recognize how useful coprolites can be. “This dinosaur ancestor was doing a bit of the fieldwork for us,” he says. “We wouldn’t have been able to find these insects otherwise.”