Global climate change and North American mammalian evolution

We compare refined data sets for Atlantic benthic foraminiferal oxygen isot ope ratios and for North American mammalian diversity, faunal turnover, and body mass distributions. Each data set spans the late Paleocene through Pl eistocene and has temporal resolution of 1.0 m.y.; the mammal data are rest ricted to western North America. We use the isotope data to compute five se parate time series: oxygen isotope ratios at the midpoint of each 1.0-m.y. bin; changes in these ratios across bins; absolute values of these changes (= isotopic volatility); standard deviations of multiple isotope measuremen ts within each bin; and standard deviations that have been detrended and co rrected for serial correlation. For the mammals, we compute 12 different va riables: standing diversity at the start of each bin; per-lineage originati on and extinction rates; total turnover; net diversification; the absolute value of net diversification (= diversification volatility); change in prop ortional representation of major orders, as measured by a simple index and by a G-slatistic; and the mean, standard deviation, skewness, and kurtosis of body mass. Simple and liberal statistical analyses fail to show any cons istent relationship between any two isotope and mammalian time series, othe r than some unavoidable correlations between a few untransformed, highly au tocorrelated time series like the raw isotope and mean body mass curves. St andard methods of detrending and differencing remove these correlations. So me of the major climate shifts indicated by oxygen isotope records do corre spond to major ecological and evolutionary transitions in the mammalian bio ta, but the nature of these correspondences is unpredictable, and several o ther such transitions occur at times of relatively little global climate ch ange. We conclude that given currently available climate records, we cannot show that the impact of climate change on the broad patterns of mammalian evolution involves linear forcings; instead, we see only the relatively unp redictable effects of a few major events. Over the scale of the whole Cenoz oic, intrinsic, biotic factors like logistic diversity dynamics and within- lineage evolutionary trends seem to be far more important.