Elephants, even now, love water. And they come by it honestly. In the Eocene period, 37 million years ago, the ancestors of elephants spent time in the water probing with their proto-trunks for aquatic plants to eat. It’s possible that the elephant’s trunk developed initially for reaching deep into the water for forage.
Two early proboscideans, Moeritherium andBarytherium, have left fragmentary remains. To tell what they ate, researchers looked at the distribution of isotopes in their teeth. The isotopes reflect a watery environment.
While carbon isotopes can give clues as to an animal’s diet, oxygen isotopes found in teeth come from local water sources – and variations in the ratios of these isotopes can indicate the type of environment the animal lived in. They compared the ratios of these isotopes to definitely terrestrial animals from the same period and these results – when combined with results from studies of embryology, molecular data, and sedimentology – lead them to believe that Moeritherium was semi-aquatic.
We already know that their closest relatives are the sirenians, or manatees and dugongs, which are fully aquatic. Researchers hope to look at other ancestors of elephants to find when they split off from sirenians and when they started feeding on land.