A Penny For Your Thoughts: An Exercise in Taphonomy

Undergraduate Historical Geology (majors and non-majors) course: used as an introduction to paleontology lecture exercise, or as part of the course's introductory paleontology fossilization laboratory.
Undergraduate required course in Paleontology; used either as a homework assignment for discussion during class lecture, or as part of a laboratory exercise on taphonomy.

Previous experience with a student's contact with handling a penny (which might not be as common as in previous generations) for payment. A student should have gained an understanding of the effects of physical abrasion on an object as well as the concept of chemical alteration of an object.

The activity is used as a homework assignment during lectures on taphonomy, fossils, and fossilization in an introductory paleontology course. It is a stand-alone exercise wherein students return to class with their answers, which are presented to their peers looking for consensus on the temporal trend(s). When consensus isn't found and the temporal trend revealed, students are asked to hypothesize on what physical and chemical processes may be responsible for the features exhibited by the coins. Subsequently, students are asked to read two papers that are pertinent on taphonomic characters in Recent shell assemblages, compare their readings to their conclusions about their analyses, and write a short compare/contrast text. Hence, a penny for their thoughts.

The exercise consist of twenty (2) images of pennies in which the mint date has been blurred. The pennies are placed into a random order, each assigned a letter designation. Using only the physical features on display (color, wearage, etc.), students are asked to place these in order from oldest to youngest. They are, then, asked to provide a hypothesis or explanation about their decision which involves an accurate description of the samples in their chosen time series.

Using color and physical condition of the coins, students must develop a hypothesis before placing the pennies into a temporal framework. As in any science, each student will develop his/her own set of criteria on which to base their analyses and conclusions. In-class discussion of the various trends will require students to evaluate other, competing hypotheses and scenarios presented by their peers. Ultimately, once the "solution" to the problem is provided, students must reevaluate their original hypothesis with new data, and learn that multiple working hypotheses continue to be refined and rewritten as new data are acquired.

A short synthetic writing exercise provides students the ability to reflect on their original ideas, how those ideas were modified as a consequence of class discussion and presentation of alternative trends, and how the introduction of new data changed their ideas.

The taphonomy (biostratinomy) exercise is designed to challenge student's preconceived ideas about the age of an individual in a fossil assemblage and the physical features that the fossil displays. A collection of 20 pennies are the proxy for the fossil assemblage. Each penny displays a different set of characters, including color (bright, superficial unoxidized [minimal circulation] to dark and oxidized [greater circulation and interaction with various chemistries] and minted relief (sharp and distinct versus worn and indistinct surface-and-edge features). The date on which each penny was minted has been removed, requiring students to develop one or more hypotheses about how to determine the relative age of coins in the assemblage. Using their hypothesis, students arrange the pennies in a time series and then justify their conclusions during class discussion. Competing student series are discussed as alternatives, demonstrating that there may be more than one way to interpret a data set, with each interpretation being equally valid. Once the answer key is provided following discussion, students are asked to reevaluate their original hypothesis and come up with factors that may have affected the appearance of the coins. Students are asked to reflect on the exercise and write a short text, comparing and contrasting their original ideas with their new ideas after being presented with additional data. This simple exercise parallels the way in which any scientist works, and shows students that science is an ever evolving inquiry for which discrete answers are not always possible.
A Penny For Your Thoughts (Acrobat (PDF) 4.1MB Aug27 21)
Instructor Keys: A Penny For Your Thoughts (Acrobat (PDF) 6MB Aug27 21)

Once students have presented their temporal trends to their classmates, discussed the variability in their analyses and explored possible physical and chemical reasons for the differences in their conclusions, and re-evaluated their original hypothesis, the instructor may want to have them read two taphonomy papers as the exercise applies to Recent bivalve assemblages. These papers act as the basis for additional discussion that may be part of a correlative laboratory activity. The two papers are:
Flessa, K.W., Kowalewski, M., and Walker, S.E., 1992, Post collection taphonomy: shell destruction and the Chevrolet: PALAIOS, v. 7, p. 553-554.
Kowalewski, M., Flessa, K.W., and Aggen, J.A., 1994, Taphofacies analysis of recent shelly cheniers (beach ridges), northeastern baja california, Mexico. Facies, v. 31, p. 209. https://doi.org/10.1007/BF02536940

Student understanding of the various factors affecting biological entities prior to burial and incorporation into the fossil record can be discerned from their reflective text on the scientific process as applied in this exercise. Colby uses Moodle as a platform for uploads, and I provided students with an informal assessment of their engagement and conceptual synthesis through the portal.

Flessa, K.W., Kowalewski, M., and Walker, S.E., 1992, Post collection taphonomy: shell destruction and the Chevrolet: PALAIOS, v. 7, p. 553-554.

Students enjoy this very short paper in which the authors note that shell damage isn't restricted to pre-burial factors or post-burial excavation. In fact, shell damage also occurs during the transport and handling of collections to the laboratory. Hence, anyone using and relying on research and museum collections for their analyses should question whether the physical features of a fossil are the result of taphonomic processes that operated when the organism was alive. Or, is the physical condition of the fossil the product of post-collection activities.

Kowalewski, M., Flessa, K.W., and Aggen, J.A., 1994, Taphofacies analysis of recent shelly cheniers (beach ridges), northeastern baja california, Mexico. Facies, v. 31, p. 209. https://doi.org/10.1007/BF02536940

Here, the authors demonstrate that various physical and chemical processes affect modern chenier plains composed of invertebrate shells, but generations of shell assemblages differ in the duration and complexity of their taphonomic history. The paper demonstrates that even assemblages that originate in the same locality over different intervals of time do not display the same shell features, similar to that of the penny exercise.