Patterns of mammalian evolution across the Cretaceous-Tertiary boundary

Abstract

The available fossil record of mammalian evolution across the Cretaceous-Tertiary (K-T) boundary is highly biased biogeographically by the results of detailed sampling of Late Cretaceous and Paleocene local faunas in what is now the Western Interior of the North American continent. In this area, which was then a coastal lowland, the mass extinction marking the K-T boundary resulted in extinction of many mammalian lineages. Analysis of the phylogenetic relationships of the mammals comprising North American early Paleocene faunas demonstrates that recovery of taxonomic diversity after the K-T boundary was the product of two processes: 1) evolutionary radiation of some locally surviving stocks and 2) immigration of mammals from other, as yet unsampled areas. Limited evidence suggests that dispersal of the groups that dominate these earliest Paleocene faunas had begun in the latest Cretaceous. Some mammalian local faunas of Late Cretaceous or early Paleocene age are known from other continents, but none of these provide as complete a fossil record of mammalian evolution during this interval. In spite of these limitations, analysis of the available, global fossil record reveals significant biogeographic provinciality of mammalian faunas and some similarities in their patterns of extinction and recovery of taxonomic diversity during the transition from the Cretaceous into the Tertiary.