Different species of the sea animals known as crinoids display different colors in these 350-million-year-old fossils. Ohio State University researchers have found organic compounds sealed within the pores of these fossilized animals’ skeletons. Credit: Photo by William Ausich, courtesy of Ohio State University
Columbus, Ohio—Though scientists have long believed that complex organic molecules couldn’t survive fossilization, some 350-million-year-old remains of aquatic sea creatures uncovered in Ohio, Indiana, and Iowa have challenged that assumption.
Buried quickly and isolated from the water above by layers of fine-grained sediment, their porous skeletons gradually filled with minerals, but some of the pores containing organic molecules were sealed intact.
The molecules appear to be aromatic compounds called quinones, which are found in modern crinoids and other animals. Quinones sometimes function as pigments or as toxins to discourage predators.
Lead author Christina O’Malley, who completed this work to earn her doctoral degree, first began the study when she noticed something strange about some crinoids that had perished side by side and become preserved in the same piece of rock: the different species were preserved in different colors.
“People noticed the color differences 100 years ago, but no one ever investigated it,” O’Malley said. “The analytical tools were not available to do this kind of work as they are today.”
Part of why the crinoids were so well preserved has to do with the structure of their skeletons, the researchers said. Like sand dollars, crinoids have skin on top of a hard calcite shell.
The location of the fossils was also key to their preservation. In the flat American Midwest, the rocks weren’t pushed up into mountain chains or heated by volcanism, so from the Ohio State geologists’ perspective, they are pristine.
Their next challenge is to identify the exact type of quinone molecules they found, and determine how much information about individual species can be gleaned from them.
“These molecules are not DNA, and they’ll never be as good as DNA as a means to define evolutionary relationships, but they could still be useful,” Ausich said. “We suspect that there’s some kind of biological signal there—we just need to figure out how specific it is before we can use it as a means to track different species.”