ENVIRONMENTAL MODELS FOR TERMINAL PLEISTOCENE MEGAFAUNAL EXTINCTIONS AND MIS 5E

One of the primary criticisms for environmental models of terminal Pleistocene megafaunal extinction is that extinctions did not occur at other times of environmental change throughout the Quaternary, especially during Marine Isotope Stage (MIS) 5e. This criticism is based on the fundamental assumption that all previous transitions between glaciation and interglaciation were the same as the transition from MIS 2 to MIS 1 and that biotas responded in similar ways to all of these fluctuations. Vertebrate faunal data and other proxies do not support this assumption. First, environmental proxies for the northern hemisphere suggest that the increased warmth of MIS 5e was primarily the result of warmer winters than those of MIS 1. Therefore, the environments of MIS 5e and MIS 1 are not equivalent. In fact, the warmer winters of MIS 5e would increase productivity in contrast to its decrease in modern seasonal patterns. Increased productivity would support a larger biomass.

Also, faunal mosaics (i.e., environmental mosaics) during MIS 5e were significantly different than those of MIS 1. These differences could have facilitated greater faunal interchange between “biomes” thus allowing for larger geographic ranges of taxa. Since a taxon’s probability of extinction decreases with increasing geographic range, extinction probability would have been significantly lower in MIS 5e than in MIS 1. In addition, these distributional patterns of the Pleistocene resulted in non-analog faunas and environments in comparison to those of MIS 1. Consequently, arguments based on the disappearance or reduction of modern environments like tundra and grassland during MIS 5e without faunal extinction are not pertinent. Finally, if the terminal Pleistocene extinction was caused by a threshold effect, then whether the changes at MIS 5e and MIS1 are the same is irrelevant.