FOSSILS AND FOSSIL CLIMATE - THE CASE FOR EQUABLE CONTINENTAL INTERIORS IN THE EOCENE

There are many methods for inferring terrestrial palaeoclimates from p alaeontological data, including the size and species diversity of ecto thermic vertebrates, the locomotor and dental adaptations of mammals, characteristics of leaf shape, size, and epidermis, wood anatomy, and the climatic preferences of nearest living relatives of fossil taxa. E stimates of palaeotemperature have also been based on stable oxygen is otope ratios in shells and bones. Interpretation of any of these data relies in some way on uniformitarian assumptions, although at differen t levels depending on the method. Most of these methods can be applied to a palaeoclimatic reconstruction for the interior of North America during the early Eocene, which is thought to be the warmest interval o f global climate in the Cenozoic. Most of the data indicate warm equab le climates with little frost. Rainfall was variable, but strong aridi ty was local or absent. The inferred palaeoclimate is very different f rom the present climate of the region and from model simulations for t he Eocene. This suggests that models fail to incorporate forcing facto rs that were present at that time, that they treat the heat regime of continents unrealistically, and/or that model inputs such as sea surfa ce temperature gradients or palaeotopography are incorrect.