The research will be presented during the 113th national Geological Society of America meeting in Boston, Nov. 1-10, 2001.
Jennifer Stempien said the basic theory in geobiology is that environmental conditions have a strong influence on the shape and size of organisms. In the past, such studies in geobiology were done over a time range of two million years, when changes in fossil shape and size are reasonably detected. "Our study is for one half million years," she said. "We’re trying to see what the shortest time interval is in which we can see change in an organism due to environmental change. We are focusing on a gradual environmental change that occurred in Southeastern Virginia 3.5 million years ago to three million years ago due to changes in sea level and the effect of that change on one species."
Stempien, along with Gwen M. Daley of the Department of Geology and Geophysics at the University of Wisconsin, Madison, and Michal Kowalewski of Virginia Tech’s Department of Geological Sciences, are using Mulinia congesta (Conrad), a small bottom-dwelling clam, in their research. The clam can be found along the Eastern seaboard, but the study focuses on those collected in Virginia and in rocks that record the environmental change. "It starts out in a high-energy environment with a lot of wave action and gradually changes to lower energy," Stempien said. "The water calmed down and became more muddy and soupy."
Organisms can possibly change in overall shape and size over time due to environmental forces. "We saw from our first analysis that in 500,000 years, there is no shape change, but only a size change," Stempien said.
Stempien’s studies will help fine tune biostratigraphy, or the use of fossils and sedimentary rock layers to figure out geologic time used by oil companies to map areas that, before, they could map with a resolution of only two to three million years. The studies also will help researchers see the amount of variability within a species or population during a shorter time period and the stability of that species as environments change. "The research can be used by evolutionary biologists, biostratigraphers, paleontologists and paleoecologists and paleo-environmental interpreters," she said.
Stempien will present the paper, "Testing for Ecophenotypic Variation Across a Paleoenvironmental Gradient in a Small Mactrid Bivalve (Yorktown Formation, Pliocene, Virginia)," on Wednesday, Nov. 7, at 3:30 p.m. in Room 106 of the Hynes Convention Center. Co-authors are Daley and Kowalewski.
Dr. Kowalewski can be reached at 540-231-5951 or michalk@vt.edu
PR CONTACT: Sally Harris 540-231-6759 slharris@vt.edu