Article: A climatic explanation for patterns of evolutionary diversity in ungulate mammals
Christine M. Janis
The radiation of ruminant artiodactyls, bovids in particular, that characterized the latter part of the Neogene, appeared to be at the expense of the hindgut-fermenting ungulates (perissodactyls, proboscideans, and hyracoids), that showed a corresponding decrease in diversity and total numbers. However, climatic and vegetational changes may have been the cause for this decline, rather than direct competition with ruminants. The Tertiary change in relative diversity of hindgut fermenters, from initially more than 50 % of the ungulate fauna to only 25-30 %, occurred during the late Eocene and early Oligocene in higher latitudes, and in the mid-Miocene in lower latitudes. In both cases, this change was correlated with a climatic shift from low to high seasonality. Subsequently, the relative abundance of hindgut fermenters remained more or less constant in all latitudes until the end of the Pleistocene. The radiation of the ruminant artiodactyls appears to have taken place at the expense of less specialized selenodont artiodactyls such as anthracotheres, oreodonts, and traguloids, that were the first artiodactyls to show an increase in diversity after the late Eocene reduction in numbers of hindgut fermenters.