Teaching Geologic Labs with 3-D Printed Media: An Experience with Fossil Horse Teeth

ELISABETH ERVIN-BLANKENHEIM (Elisabeth.Ervin@frontrange.edu) is a geology instructor at Front Range Community College, Fort Collins, CO, and a doctoral student at St. Francis Xavier University, Antigonish, Nova Scotia.

Few topics are of more interest to students of all ages than fossils. At this time of critical climate change and environmental challenges, an understanding of science in general and geology in specific can be of great use by providing the context of geologic time and knowledge from similar events from the past. Geology is a historical science. It differs from other sciences and lends itself to a more holistic study of the Earth. As such, geology has a unique role in conveying overarching principles and providing a framework for understanding the natural world. According to Dodick and Argamon (2006), when compared to "hard sciences," "historical science...investigates ultimate causes that often lie very deep in the past, and the effects of which are observed only after very long and complex causal chains of intervening events. Consequently, evidence is gathered by observation of naturally occurring traces of phenomena, since manipulation is impossible (e.g., we cannot wait millions of years for the results of a hypothetical geological experiment!)." Scientific ideas can be complex to impart to students because of the specific language and other barriers to knowledge inherent in each field. There is a need for a narrative in teaching science (Millar and Osborne, 1998): "...science education should make much greater use of one of the world's most powerful and pervasive ways of communicating ideas -- the narrative form -- by recognizing that its central aim is to present a series of 'explanatory stories.'"

The question is, how do Earth science instructors, teachers, and professors engage students in an interactive manner with fossils to build a narrative that will help them fathom geology? The answer may lie in fossils of a different sort—those that have been scanned, saved as 3-D images, and uploaded to sites for study. Fossil materials are difficult to come by and expensive to purchase. Most institutions have budgetary constraints and, further, may not have access to collections which could be used for study. Accessible 3-D fossils are available to counteract these limitations. Many 3-D printing labs have the facilities to create the materials from the associated files.

In the example discussed here, fossil horse teeth are used for an experiential, hands-on lab. The original fossils, excavated from North American sites in Nebraska, Wyoming, and Florida, are housed at the Florida Museum of Natural History, University of Florida. The specimens were scanned through micro-CT imaging by the Florida Museum staff; the 3-D files were then created and placed on the Morphosource website (Boyer et al. 2015) with associated instructional materials. The 3-D files were downloaded to develop this lab experience, with permissions, through the Morphosource database—free for non-commercial use. The fifteen-piece set was printed using 3-D technology for approximately $40. The files were printed in a powder bed of gypsum to create the most representative replicas and without forming a substrate that would need to be cut. Gypsum powder can be tinted, and the process results in media that have a natural feel as compared to plastic models. This experiential lab is based on work by Broo and Mahoney (2015) and Bokor, Broo, and Mahoney (2016). Guide- lines, worksheets, and slides for the lab, called "Chewing on Change" (Broo and Mahoney, 2015), are available free online (see REFERENCES). The lab was adapted to enhance the story-telling aspects of horse evolution.

Fossil horse teeth from the Eocene to the Pleistocene (55 million years ago to 10,000 years ago) comprise the collection available through Morphosource. The fifteen teeth trace the story of horses and horse ancestors through geologic time as the climate shifted from warm, tropical climes with abundant forests to open, dryer savanna vegetation as the climate cooled and the first grasses developed. The lab experience described here follows this history and interweaves geologic time, evolution of animals and plants, and changes to the climate in the Earth's past. Thus, the interrelatedness of different parts of the planet— environmental conditions and life— are highlighted.

Many students relate to horses or have had experiences with equines. Most do not know that horses evolved in North America and ranged on the continent for many geologic epochs until the great Pleistocene extinctions 10,000 years ago. The geologic and evolutionary history of horses can offer a rich, multilayered experience through the use of fossil teeth.

American educator John Dewey promoted the role of experience in teaching (Dewey, 1938). He advocated for engaging hands-on lessons combined with reflection on the part of the teacher and the students. Dewey believed this method was more effective compared to the traditional type of teaching whereby the instructor, as the expert, lectured and the students, as receptacles, absorbed the material. The lab presented here is an example of a Deweyian approach. The instructor may begin with an overview presented before the laboratory experience to introduce basic ideas for the lab and highlight pertinent facts about horse evolution. The quantitative portion of the lab involves students gathering in groups to measure the 3-D printed fossil horse teeth using calipers. After recording the measurements, students divide the height of the tooth by its width at the crown to create a hypsodonty index (HI).

The HI is a measure of how high the teeth extend above and how far they continue below the gum line. Animals with a high HI are hypsodonts, have high crown, deeply rooted teeth, and are adapted to digest tough vegetative material like grasses. Conversely, animals with a low HI are brachydonts, have low crown, shallowly- rooted teeth, and are suited to browse on the relatively soft forest vegetation. Hypsodonty data illustrate the change in horse teeth over geologic time from browsers to grazers. The HI increases as the teeth elongate in response to changes in vegetation. Students plot the data on an XY scatter chart with geologic time on the horizontal axis an the HI value on the vertical. Next, they overlay the range of times representing the geologic epochs in color on the graph to see changes in the fossil teeth through geologic time. The example graph is plotted with the epochs in the colors of the geologic time scale, but other colors could be selected. These procedures may be enough for one session or the students can continue on to th next section.

The qualitative, narrative part of the lab involves providing the students 81⁄2 x 11-inch cards with different kinds of data—climate and vegetation information, a pictorial environmental depiction for each geologic epoch (Eocene example on page 1), and data related to horse ancestors through time, body dimensions, fossil teeth, and morphology of their feet.

Students groups sort the cards into geologic-age order, and then data are associated with the particular geologic epoch. This process forms the basis for the students to create the story of horses through time. Each group writes its own narrative on the geologic history of horses and reports back to the class on what they have discovered.

The instructor provides times for discussion and a wrap-up. Topics which may be covered are a summary of and feedback on the narratives produced by each group along with questions about horse evolution. Climate events, such as the warming in the Eocene and later in the Miocene, and their impacts on life also can be introduced. Complexity in evolution may be presented. The way in which the evolution of horses has been shown in the past as linear function, with one ancestral horse morphing into the next species, has transformed with current research to a new understanding (MacFadden, 2005) in which different horse forebearers lived at the same time and may have competed for similar food sources.

Using 3-D printed media to understand the history of horse ancestors through changes in fossil teeth can be a way for students to have an experience of geologic time, thus providing a lens through which to view Earth and problems on the planet in a new way. This is a narrative, story-telling approach and combines changes in life forms in response to climate and environmental pressures occurring over geologic time. It is different from other methods of teaching the time scale in that it is a more holistic and, therefore, a more relatable view of one species -- the beloved equine.

REFERENCES

Bokor J,. Broo J., and Mahoney, J., 2016, Using fossil horse teeth to study the evolution in horses in responses to a changing climate: The American Biology Teacher, v. 78, no. 2, p. 166-169, doi: 10.1525/abt.2016.78.2.166.

Broo, J., and Mahoney, J., 2015, Chewing on change: Exploring the evolution of horses in response to climate change: Gainesville, FL, University of Florida, 12 p. (Available at https://www.cpet.u .edu/ resources/curricula/created-by-fellows/evolution/)

Boyer, D., Grant, C., Moran, S., and Ziegler, M., 2015, ProjectK12–Horseevolution, Morphosource database. (Available at https://www.morphosource. org/Detail/ProjectDetail/Show/project_id/144)

Dewey, J., 1938, Experience and Education: New York: Kappa Delta Pi, 91 p.

Dodick, J., and Argamon, S., 2006, Rediscovering the historical methodology of the earth sciences by analyzing scientific communication styles, in Manduca, C., and Mogk, D.W., eds., Earth and mind: How geologists think and learn about the earth: Boulder, Colorado, Geological Society of America, Special papers 413, p. 111.

MacFadden, B.J., 2005, Fossil horses – Evidence of evolution: Science, v. 307, no. 5716, p. 1728-1730.

Millar, R., & Osborne, J. (Eds.), 1998, Beyond 2000 – Science education for the future: Seminar series of the Nuffield Foundation. London, UK: Kings College, p. 2011-2032. (PDF available for download at https://www.nuffieldfoundation.org/beyond-2000-science-education-future)

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