Mammalian Evolution in the Paleocene: Beginning of an Era

Extract

The Paleocene (approximately 65 to 55 million years ago) is the first epoch of the Cenozoic Era; it is also the beginning of an era in which mammals underwent a major adaptive radiation and became dominant land animals. It was a fascinating and exciting era of transition in mammalian evolution between the dark ages of the Cretaceous, when mammals were few and small and lived in the shadow of the great, “ruling reptiles”, and the explosive ages of the Eocene, when mammals were diverse and in full blossom. In the Late Cretaceous there were approximately eight families of marsupials and placentals; by the early Eocene over 70 had come into being. Were mammals from the Paleocene totally unknown, creationists would surely have plenty of grist for their missing-link mills. But Paleocene mammals are now known from five continents and they give evidence of archaic groups of mammals that were unleashed from the constraining suppression of dinosaurs. Paleocene mammals evolved rapidly and included “evolutionary experiments” that failed soon thereafter but also groups that were at the base of enormously successful adaptive radiations later in the Cenozoic. In fact, more than one-third of the known orders of the Cenozoic had their beginnings, or origins, in the Paleocene. Origins are captivating. At one time or another every one of us has pondered the origin of the universe, the origin of life, the origin of humankind, etc. Without knowledge of Paleocene mammals, many basic questions concerning the origin and evolution of mammalian adaptations would not be answerable.