A simplistic view of the Aquatic Ape theory - hairless mammals spent a long time living in the water, once upon a time. Elephants are amazing swimmers, and it surprises me that scientists are surprised to find that the ancestors of elephants could also swim:

"A prehistoric ancestor of the elephant may have roamed — and perhaps swum — farther than experts once imagined. "

The fossil of a 7 million year old Deinotherium Gigantisimum, 15 feet tall, found in Crete,

"suggest the mammal moved around larger areas of Europe than previously believed, possibly swimming long distances in search of food. "

They also believe that skulls of the animal, with a large hole for where the trunk connected, gave rise to the myth of Cyclops.