GEOGRAPHIC INFORMATION SYSTEM ANALYSIS OF THE DISTRIBUTION OF LIVING REPTILIANS WITH RESPECT TO CLIMATE AND ITS POTENTIAL FOR GENERATING QUANTITATIVE PALEOCLIMATIC ESTIMATES

Through the use of Geographic Information System (GIS) technology (ArcMap), biogeographic ranges of North American turtles, lizards, and crocodilians were plotted and overlain to generate biodiversity maps for reptilian groups (guilds) which were then analyzed against nine climate maps representing measurements of temperature, seasonality, environmental moisture, and solar radiation.

When diversity was regressed against climatic parameters, minimum and maximum climatic values were linked with the biodiversity of each reptile guild. The X-Y plots produced by linear regression analyses provide minimum and maximum climatic values associated with guild diversities and the overlap of the ranges of different estimates can then be used to establish criteria for assessing paleoclimatic conditions based on reptilian diversity in well sampled fossil assemblages.

Crocodylids are restricted by cool mean annual and cold month temperatures and high seasonal temperature change. Lizard diversities have strong positive correlations with high mean annual temperature, solar radiation, and low rainfall. Aquatic and semiaquatic turtle diversities have strong positive correlations with high mean annual temperature, warm summers, and high humidity but are restricted by high seasonal temperature change and low cold month temperature. Terrestrial turtles thrive with low seasonality and warm summers but unlike aquatic turtles, are less controlled by cold month temperatures and environmental moisture.

These climatic limits were then applied to fossil assemblages (approximately 60,000 University of Michigan Museum of Paleontology specimens) from the Paleocene and Eocene of western Wyoming to create paleoclimate estimates. Analysis of these faunas indicate mean annual and cold month temperatures, seasonal temperature changes, and mean annual precipitations that were similar to conditions that exist today along the Gulf Coast of North America. The current data indicates relatively minor climatic change through most of the early Paleogene, but supports a warming and wetting of the area into the middle Eocene about 50Ma. This research hopes to contribute both to the paleoclimate record and to the understanding of biodiversity as it changes in response to a dynamic earth and atmosphere.