SANTA CRUZ, CA -- As any swimmer knows, moving through water is nothing like moving on land. When the ancestors of modern marine mammals first ventured into the ocean some 60 million years ago, they had to adapt to a medium 800 times denser and 60 times more viscous than air. The spectacular success of their descendants illustrates the remarkable power of natural selection.
According to a new study comparing the athletic abilities of different types of animals, modern marine mammals are so well adapted to aquatic life that they are as efficient in swimming as specialized land mammals are in running. Terrie Williams, an associate professor of biology at the University of California, Santa Cruz, found that elite animal athletes, from horses to killer whales, achieve an optimal efficiency for locomotion that is determined more by their basic mammalian physiology than by their mode of transportation.
"The bottom line is that terrestrial and marine mammals expend similar amounts of energy to live and move in their respective environments," said Williams, who has been studying the exercise physiology of terrestrial and marine mammals for over 20 years.
In an article published this month in the Philosophical Transactions of the Royal Society of London, Biology, Williams presented a comprehensive analysis of the energetic costs of locomotion in terrestrial, aquatic, and semiaquatic mammals. She also extended her comparisons to include flying mammals (bats), as well as fish and birds.
Her findings indicate that for specialized mammals, whether they run across the plains, swim through the oceans, or fly across the evening sky, the energetic cost of moving through the environment is about the same. Some may achieve higher speeds than others, but their efficiency -- the amount of energy required to move a set distance -- appears to be constrained by a physiological limit for the mammalian way of life.