WHAT WAS THE MEAN ANNUAL TEMPERATURE OF FLORISSANT, COLORADO, DURING THE LATE EOCENE?

Estimates of the mean annual temperature based on the Florissant paleoflora range from as low as 10.7° C to as high as 18°C. The Florissant flora includes a mixture of conifers and deciduous trees that have modern relatives with widely dispersed modern geographic ranges. These include trees now found in the California and Oregon coasts, the eastern United States, southern United States and northeastern Mexico, eastern Asia, and the modern Rocky Mountains. Despite this wide range in distributions, a floristic analysis based on the temperature ranges of the modern related genera of these plants have produced higher temperature estimates (17.5°C to 18°C). Because of this geographic and climatic variety, and questions as to the relations of the paleotaxa to modern taxa, various non-taxonomic methods of estimating temperature have been used to estimate mean annual temperatures. These include leaf-margin analysis, comparisons with Asiatic leaf associations, and multivariate climatic analyses. These methods result in lower estimates of mean annual temperatures ranging from 10.7°C to 14°C. The fauna of Florissant is also ambiguous as to the temperature estimates, but the presence of subtropical tsetse flies and mouse opossums suggest warm conditions with little or no frosts. These temperature estimates are especially important in the estimating the late Eocene elevation of Florissant. Depending on the kind of analysis and the mean annual temperature estimate used in the analysis, the paleoelevation estimates range from essentially the same elevation as today, to 1.5 km lower than today, to 1.7 km higher than today.