2004 Denver Annual Meeting (November 7–10, 2004)

Paper No. 1
Presentation Time: 1:30 PM


BARRETO, Claudia, Biological Sciences, Univ of Wisconsin Milwaukee, PO 413, Milwaukee, WI 53201, SHEEHAN, Peter M., Geology, Milwaukee Public Museum, 800 W. Wells St, Milwaukee, WI 53233 and FASTOVSKY, David E., Department of Geosciences, Univ of Rhode Island, 9 East Alumni Ave, Kingston, RI 02881, barr@uwm.edu

To study nature, scientists design experiments, a key component of which are systematic plans to collect data that will enable them to validly test hypotheses. For example, to understand the “great dying” at the end of the “age of reptiles” it is necessary to first determine the rate and pattern of extinction and subsequently examine plausible causes for the observed ecological episode. In a study by Sheehan and others (1991), evidence led to the conclusion that the community of animals living in the Upper Great Plains was thriving and then suddenly wiped out 65 million years ago. This scenario is based on a comprehensive survey that documented the numbers and kinds of dinosaurs living in an area now preserved as the Hell Creek Formation, over the final 2.1 million years of the Cretaceous Period. To amass a database adequate in size to reconstruct the population dynamics of this community, data on over 2,000 in place fossils were recorded. Because dinosaur fossils are rare (Sheehan and others, 2000) this challenging task was carried out by 150 amateurs who were closely supervised by project scientists (15,000 hours of fieldwork were logged). Volunteers were recruited through the Milwaukee Public Museum Dig-a-Dinosaur Program. An added benefit of having volunteers assist in data collection is that they have no preconceived biases on what kinds of dinosaurs they would find and where (spatially and temporally) within the study area they would find them. Thus, is was possible to compare equivalent data sets, documenting the numbers and kinds of dinosaurs (ecological diversity) in the lower, middle and upper thirds of the formation to test for changes in population structure over time that would disclose whether the extinction occurred gradually or abruptly. Data analysis led to acceptance of the latter hypothesis, a pattern that is consistent with a catastrophic cause, such as the impact of an asteroid with the earth.