Return to the Sea portrays the life and evolutionary times of marine mammals--from giant whales and sea cows that originated 55 million years ago to the deep-diving elephant seals and clam-eating walruses of modern times. This fascinating account of the origin of various marine-mammal lineages--some extinct, others extant but threatened--is for the nonspecialist. Against a backdrop of geologic time and changing climates and geography, this...