Answers from Dr. Frank Fish
Read Dr. Fish's answers to your questions.
Q: If mammals are evolved to live in water, does it suggest that a sea lion, for instance, which lives sometimes in water and sometimes on land, could someday live totally in water, like the whales?
— D. Tong
A: Not the sea lion, but maybe its descendent could live totally in water. A lot would depend on the selection pressures that would tend to make other species descended from the sea lion want to stay in the water. The biggest hurdle to overcome would be mating and giving birth in the water. As the pups of sea lions require a period of time after being born to develop and grow before their first swimming lesson. The evolution of new, more aquatic sea lions would require that the young be more adapted to the sea.
Q: What if mammals never took to the water? What might the world look like today?
— L.H.
A: From my perspective, the world would have missed out on one of the most intriguing groups of animals, the marine mammals. The largest of all animals that have ever lived, fast, intelligent, whales, seals, and sea lions are truly a sight to behold. If they had never evolved, we could only speculate that birds and fish may have taken the marine mammals' place. Penguins are fast-swimming, fish-eaters and there are a number of birds that fish and dive in the water. If birds could get to the size of an ostrich or elephant bird on land, why couldn't they become as large or larger in the water?
On the other hand, sharks may have been able to occupy the niche of marine mammals. Some sharks are very fast swimmers and are warm blooded. Great white sharks are warm-blooded and excellent predators. Whale sharks and basking sharks are specialized for filter feeding, similar to baleen whales.
Q: Do we know anything yet about when the manatee began to go aquatic? And if there are any living relations?
— A. and S. Cunningham
A: The closest relatives of the manatees besides the dugong (also a member of the Sirenians) are elephants. The sirenians diverged from other mammals about 55 million years ago. These early sirenians had legs and moved on land, but would eventually loss the legs as they became more aquatic. The genus for the manatee, Trichechus, evolved about 5 million years ago.
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