Researchers have discovered a new species of insect in fossil faeces: the tiny beetle Triamyxa coprolithica. It was probably consumed around 230 million years ago by a Silesaurus, a bird-like dinosaur ancestor from Poland weighing around 15 kilograms. A special microtomography revealed that the animal’s feces were preserved in such an excellent way as is otherwise only known from amber. In the future, fecal fossils could provide more detailed insights into the early evolution of insects and shed light on the diet of early vertebrates.
The best preserved insect fossils known to date come from amber. Enclosed in tree sap, her body has survived almost unchanged for millions of years. However, amber was mainly formed in a relatively recent geological period. The oldest amber fossils are around 140 million years old. There are only a few well-preserved insect fossils for the time before. Because the delicate structures of the rather small animals are seldom preserved in detail during fossilization.
230 million year old legacies
A team led by Martin Qvarnström from the University of Uppsala in Sweden has now discovered an alternative to amber that allows much more glimpses into the past: petrified fecal samples, so-called coprolites. With the help of a special scanning process, they found exceptionally well-preserved beetle fossils in the legacy of a dinosaur ancestor, which is around 230 million years old. Among them were a few almost complete specimens, in which the delicate legs and antennae were still intact.
“We were absolutely amazed at the abundance and the fantastic preservation of the beetles in the coprolite fragment,” says Qvarnström. “When you modeled the beetles on the screen, it was like they were looking directly at you. The preservation was favored by the calcium phosphate-containing composition of the coprolites. This, along with the early bacterial mineralization, likely helped preserve these delicate fossils. “
New species of beetle identified
The good state of preservation of the fossils enabled the researchers to identify the beetles found as a new species, describe them in detail and compare them with more modern relatives. The research team named the new beetle species Triamyxa coprolithica – a reference to its location in a coprolite. Modern relatives of the extinct species of beetle live in humid environments and feed on algae, and Triamyxa coprolithica probably had a similar habitat.
The fecal sample in which the beetles were found probably comes from a Silesaurus opolensis, a dinosaur ancestor about two meters long and weighing 15 kilograms, who lived in present-day Poland 230 million years ago. “Although Silesaurus seems to have devoured numerous individuals of Triamyxa coprolithica, the beetle was probably too small to have been the only targeted prey,” explains Qvarnström. “Instead, Triamyxa likely shared its habitat with larger beetles, represented by individual remains in the coprolites, and other prey that did not end up in the coprolites in a recognizable form. So it seems likely that the Silesaurus was omnivorous and that part of its diet consisted of insects. “
Petrified droppings as a treasure trove
“I never thought that we would be able to find out what the Triassic forerunners of the dinosaurs ate for dinner,” says Qvarnström’s colleague Grzegorz Niedźwiedzki. The study shows that coprolites can be valuable for studying early insect evolution and, at the same time, the diet of extinct vertebrates. “There are tons of things that fossilized feces can examine, but it’s been hard to understand what to do with it, hard to see what’s in it, and hard to draw conclusions – but now there are tons of data, ”says Qvarnström. “The ultimate goal is to use the coprolith data to reconstruct ancient food webs and see how they have changed over time.”
Source: Martin Qvarnström (University of Uppsala, Sweden) et al., Current Biology, doi: 10.1016 / j.cub.2021.05.015