Trophic model for the adaptive radiations and extinctions of pelagic marine mammals

Abstract

Pelagic marine mammals (cetaceans and pinnipeds) generally invaded the seas rapidly in response to new ecologic opportunities. After cetaceans initially appeared and radiated in the Eocene, they declined in the Oligocene, but radiated into many new adaptive types in the Miocene. Pinnipeds apparently evolved in the earliest Miocene, rapidly radiating into many adaptive types. We propose that the radiations, and declines, of species were responses to the availability of trophic resources in oceanic environments. These trophic resources are closely related to upwelling processes in the oceans. We suggest that increased upwelling intensity, due to climatic or tectonic events, permitted the initial invasions and radiations and that decreased intensity caused cetacean extinctions in the Oligocene.