Most fossils, while intellectually exciting, are not all that pretty to look at.One notable exception are crinoids. Also known as sea lilies, their flowerlike appearance can be stunning.
Most fossils, while intellectually exciting, are not all that pretty to look at.One notable exception are crinoids. Also known as sea lilies, their flowerlike appearance can be stunning. Crinoids are echinoderms and are related to starfish, brittle stars and sea urchins (including the flat ones called sand dollars).Take a starfish, make its arms feathery, turn it upside down so the mouth is pointing upward and put it on a long stem, and you have a crinoid. Crinoids are sometimes playfully referred to as “starfish on a stick.”
The Edwardsville formation in southern Indiana, deposited early in the Mississippian Period around 340 million years ago, contains a large number of well-preserved crinoid fossils.An interesting feature of those fossils is that different species of crinoid are preserved in different shades of gray.A recent research paper looked at those color differences and came up with some interesting results.The paper was written by lead author Christina O’Malley, a former Ohio State University graduate student, and William Ausich and Yu-Ping Chin, both of the School of Earth Sciences at Ohio State.
Dissolving the fossils in hydrochloric acid, the team extracted the resulting chemicals and found biomarkers, which are chemicals produced only by living organisms. These are the oldest biomarkers ever extracted directly from fossils.The same chemicals were not found in the surrounding rock, which shows that those chemicals were not recent contaminants.
Even more intriguing, different species produced slightly different biomarkers. Such differences might be used to work out more-detailed family trees of these species or possibly to determine what colors they were in life. Modern echinoderms exhibit a remarkable range of colors — bright blues, brilliant oranges, deep greens and reds, hot pinks, canary yellows — and ancient species were probably equally colorful.
How could biomarkers, generally thought of as relatively fragile compounds, be preserved for 340 million years? The authors suggest three factors.
Firstly, the animals were buried in fine-grain sediment that isolated them from exposure to fluids moving through the enclosing rocks.
Secondly, the skeletons of crinoids, like those of all echinoderms, are composed of numerous plates, each of which is a single porous crystal of the mineral calcite. In life, those pores are filled with soft tissue. After death, those pores are rapidly filled with more calcite, trapping organic material inside.
And thirdly, the enclosing rocks were never subjected to high heat caused by metamorphism, igneous activity or deep burial.Fossils of a totally different group of organisms called conodonts change color depending on the amount of heat they endure. Conodonts found in the same rocks as the crinoids show no heat alteration.
Want to see fossils including crinoids? The Central Ohio Mineral, Fossil, Gem and Jewelry Show is Saturday and Sunday at Franklin County Veterans Memorial, 300 W. Broad St.Bring in your rocks, minerals, fossils and gems for identification. I’ll see you there.
Dale Gnidovec is curator of the Orton Geological Museum at Ohio State University.