“Living” molecules, meaning intact cellular structures that haven’t fossilized, were recently retrieved from 350-million-year-old remains of aquatic sea creatures uncovered in Ohio, Indiana, and Iowa, according to a study that will appear in the March issue of the journal Geology.
The animals- crinoids- were spindly and had feathered arms. Their relatives today are called by the plant-like name “sea lily.”
The retrieved molecules are quinones, which function as pigments or toxins (to help ward off predators) and are still found in modern sea lilies. The molecules aren’t DNA, unfortunately, but they can reveal other things about past life, such as the color of long gone animals.
“There are lots of fragmented biological molecules — we call them biomarkers — scattered in the rock everywhere,” William Ausich, professor in the School of Earth Sciences at Ohio State and co-author of the paper, said in a press release. “They’re the remains of ancient plant and animal life, all broken up and mixed together. But this is the oldest example where anyone has found biomarkers inside a particular complete fossil. We can say with confidence that these organic molecules came from the individual animals whose remains we tested.”
The ultra ancient crinoids appear to have been buried alive in storms during the Carboniferous Period. At that time, North America was covered with vast inland seas. The skeletal remains of the buried-alive crinoids filled with minerals over time, but some of the pores containing organic molecules were miraculously sealed intact.
This finding helps to negate the prior belief that complex organic molecules cannot survive fossilization.
Lead author Christina O’Malley, from Ohio State too, began the study when she noticed something strange about crinoids that had perished side by side and became preserved in the same piece of rock. She observed that the various species were preserved in different colors.
In one rock sample used in the study, one crinoid species appears a light bluish-gray, while another appears dark gray and yet another more of a creamy white. All stand out from the color of the rock they were buried in. The researchers have since found similar fossil deposits from around the Midwest.
“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.”
She and her team employed a high tech machine called a gas chromatograph mass spectrometer to vaporize a liquid mixture that contained small bits of the ground up fossils. Computer software identified some of the resulting molecules as quinones.
The researchers next compared these molecules with ones from living sea lilies. As the scientists suspected, quinone-like molecules occur in both living sea lilies and their fossilized ancestors.
While “mummified” dinosaurs have yielded 66-million-year-old organic material, this level of preservation is exceedingly rare. And consider that these prehistoric sea lilies lived long before the first dinosaurs.
Crinoids tend to preserve really well because, like modern sand dollars, they possess a skin on top of their hard shells, which consist of stacked calcite rings. Calcite is a mineral made up of calcium carbonate. It is stable over geologic time, so organic matter may be protected by it when sealed whole.
“We think that rock fills in the skeleton according to how the crystals are oriented,” Ausich said. “So it’s possible to find large crystals filled in such a way that they have organic matter still trapped inside.”
“These molecules are not DNA,” he added, “and they’ll never be as good as DNA as a means to define evolutionary relationships, but they could still be useful. 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.”
Image: A modern crinoid, NURC/UNCW and NOAA/FGBNMS