All otters seek most or all of their food in water, and they've had a long time to adapt to this way of life. Their first distinctly aquatic ancestor dates back 30 million years, according to the fossil record, which shows that ancestors of the North American river otter (Lontra Canadensis)crossed the Bering Land Bridge and arrived in North America by the Upper Pliocene epoch. The earliest otters had sharp cutting teeth, which suggests that they were first attracted to water by fish rather than by hard-shelled invertebrates like crabs and crayfish. In this regard, river otters resemble these ancestors more closely than do other kinds of otters.