South American Ungulate Evolution and Extinction

Abstract

Because of its variety, good fossil record, and history of biogeographic isolation, South America’s indigenous land-mammal fauna has figured prominently in the formation of our current concept of macroevolutionary process and pace (e.g., Simpson, 1953, 1965). Throughout the Tertiary, this autochthonous fauna was dominated by distinctive and or-dinally endemic ungulate groups, not all of which were hooved and all of which are now wholly extinct. Together with the South American edentates (order Xenarthra) and marsupials, these ungulates comprise the continent’s “ancient immigrant” faunal stratum (Simpson, 1965). General interest in South American ungulate groups stems from the facts that they include forms that converged remarkably on their unrelated ecological vicars in Holarctic faunas, that they underwent adaptive radiations correlated with climatic change, and that the introduction by immigration of adaptively similar mammals in the Oligocène and at the end of the Tertiary provides a testing ground for hypotheses regarding competition among herbivores, food as a diversity-limiting resource, predator-prey coevolu-tion, and so forth.