Introduction

Abstract

Marine mammals are a diverse group with species in three taxonomic orders: Artiodactyla (infraorder Cetacea), Carnivora (clade Pinnipedia and sea otters), and Sirenia. Their ancestors were terrestrial mammals that secondarily became aquatic, and each group has a unique evolutionary history. The one commonality is that they obtain food in an aquatic environment even though they are found in diverse hydrographic habitats and have different locomotory modes and foraging strategies. However, they all show varying degrees of morphological and physiological adaptive convergence for an aquatic life. Morphology and physiology constrain an animal’s behavior and physical performance. Over time, abiotic and biotic selection pressures modify behavior and enhance performance for a particular habitat, although they are often a compromise to competing demands that ultimately determine survival and fitness. The adaptations we recognize in marine mammals today are the result of ~5 million (sea otters) to 50 million (Cetacea and Sirenia) years of evolution. This book examines adaptations that enable extant marine mammals to perform efficiently and maintain physiological homeostasis in the marine environment.