How Bacteria Help Create Dinosaur Fossils

As stated in many popular-audience books and documentaries, the fossilization of a skeleton involves the gradual transformation of bone into stone, often by way of mineral-rich groundwater percolating through bones over a long period of time. Yet things are not that simple. Thanks to recent discoveries, we know that remnants of soft tissues and even original chemical components of bone can remain preserved for many millions of years, and even though the creation of fossilized bones is often portrayed as a geologic process, a new study published in the journal PALAIOS suggests that the activity of bacteria may play an important role in how fossils form.

Most studies that have considered the role of bacteria in fossilization have focused on how bacteria breaks down bone—in order for a skeleton to be preserved in the fossil record, conditions for fossilization must be in place before the microscopic organisms entirely destroy the material. As argued by scientists Joseph Daniel and Karen Chin, however, some preliminary experiments using cubes of bone have suggested that bacteria may also foster bone preservation in some circumstances, and they designed a new experiment to test the idea. The setup, simply put, involved placing cubes of cow bone in river sand for three months while water saturated with calcium carbonate was percolated through them. Four trials were run, but in two of them sterilizing agents were added to the setup in order to remove the presence of bacteria. By doing this, the scientists could observe whether bacteria played a significant role in the preservation or degradation of the bone cubes.

At the end of the experiment, Daniel and Chin noticed significant differences between the bones used in the "natural" and bacteria-reduced trials. The cow bone from the natural trials showed a significant amount of mineral deposition within the bone, that is, the beginnings of fossil preservation. The bone from the trials in which antibacterial agents were introduced, however, apparently did not change at all—it was virtually indistinguishable from fresh, untreated bone cubes.

Even though the role of groundwater and other factors remains important to the formation of fossil bone, the results of the experiment suggest that the activity of bacteria play an important role in introducing minerals into bone during early stages of preservation. In fact, if bacteria precipitate minerals while consuming organic material inside a carcass, they may effectively create mineral barriers within bones, thereby cordoning off soft materials that can become preserved for long periods of time in the right conditions. What this means is that, shortly after the death of an organism, minerals precipitated by bacterial activity may be more important to preserving parts of bone than minerals precipitated through inorganic means—there are important biological aspects of the fossil preservation that are just now beginning to be understood.

References:

JOSEPH C. DANIEL and KAREN CHIN (2010). THE ROLE OF BACTERIALLY MEDIATED PRECIPITATION IN THE PERMINERALIZATION OF BONE PALAIOS, 25, 507-516 : 10.2110/palo.2009.p09-120r

Riley Black | | READ MORE

Riley Black is the author of The Last Days of the Dinosaurs and many other books. She is a science correspondent for Smithsonian magazine covering fossils and natural history, and she writes about the prehistoric past for a variety of publications.