Over the past 55 million years mammals have returned to the sea many times and in many places annalisa berta leads readers through this parade of transitions highlighting how marine mammals have met the evolutionary challenge of living an aquatic life in a variety of ways return to the sea weaves ecology anatomy and evolution into an ideal entry point for anyone interested in knowing more about one of the most fascinating phenomena in macroevolution nicholas d pyenson national . Return to the seaportrays 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 non specialist set against a backdrop of geologic time changing climates and changing geography evolution is the unifying principle that helps . Request pdf return to the sea the life and evolutionary times of marine mammals return to the sea portrays the life and evolutionary times of marine mammals from giant whales and sea cows . Return to the sea the life and evolutionary times of marine mammals by annalisa berta