Ever want to curl into a ball? Here's how trilobites did it
When the going got tough in the Paleozoic Era, trilobites rolled up. Armed with sturdy exoskeletons, these ancient arthropods curled up like armadillos to avoid predators or dangerous environmental conditions on the seafloor.
Many trilobites have been found with their exoskeletons fossilized in a curled position. But few preserve the internal anatomy that trilobites used to form a defensive ball.
“While enrolled trilobite fossils are really common, we don't have any of the ventral soft tissue preserved,” said Sarah Losso, a doctoral candidate at Harvard University who specializes in trilobite evolution.
Losso and her colleagues may have finally unfurled the mystery of tumbling trilobites by using a cache of impeccably preserved fossils. Their findings, published in the journal Proceedings of the Royal Society B, describe the interlocking anatomy of a rolled-up trilobite for the first time.
The trilobite fossils examined in the new study came from central New York's Walcott-Rust Quarry, where a mudslide 450 million years ago smothered an entire community of the scuttling sea creatures. Discovered by paleontologist Charles Doolittle Walcott in 1870, the site yielded the first traces of trilobite appendages and soft-tissue features like gills.
Walcott's trilobite fossils, and thin sections he sliced out of them, are stored at the Museum of Comparative Zoology at Harvard University. Losso was analyzing the trilobites' appendages when she came across a curled Ceraurus trilobite with a set of plates called sternites lining its stomach that rarely survives fossilization. “When I found that specimen, that's when I got excited,” Losso said. “We don't have these plates in enrolled, three-dimensional specimens.”
The researchers used micro-CT scans to analyze the inner anatomy of the fossil, which they describe as enrolled, and examined the thin sections Walcott made in the 1870s. Because Ceraurus trilobites had spiny shells, they folded more than they rolled. “It's a lot more like a taco than a perfect ball,” Losso said.
These thin sections provided the researchers with the most complete view yet of how trilobites rolled up, revealing the central roles played by both the arthropod's stomach plates and appendages.