Elephants share a common aquatic ancestor with manatees and dugongs, according to a paper released in PNAS.

“It has often been assumed that elephants have evolved from fully terrestrial ancestors and have always had this kind of a lifestyle,” says one of the study’s authors, Erik Seiffert of the Stony Brook University, New York (BBC). “Now we can really start to think about how their lifestyle and behaviour might have been shaped by a very different kind of existence in the distant past.”

Seiffert and colleagues analysed the composition of teeth from early elephant Moeritherium and appear to have confirmed previous suspicions that it was amphibious. “We now have substantial evidence to suggest that modern elephants do have ancient relatives which lived primarily in water,” says fellow author Alexander Liu, of the University of Oxford (press release).

In her paper, Liu notes that there have been morphological and paleontological suggestions of a common aquatic ancestor but “independent tests of this hypothesis have proven elusive”. However oxygen isotopes in teeth provide a potential solution as the ratio isotopes differs between aquatic and terrestrial animals.

Sure enough, teeth from Moeritherium and anther proto-elephant Barytherium show that it likely spent much of its time lolling around in water chopping on freshwater plants.

This isn’t the first time teeth have been used in this way. Back in 2000, UC Santa Cruz researchers reported that a large prehistoric rhinoceros seemed to have enjoyed a hippo-like lifestyle (press release). And last year researchers used teeth isotopes to show that a “small, stocky” beast that “looked similar to a mini deer” may have been an ancestor of the whale (Nature; subscription required).

More coverage

Elephant ancestors were semi-aquatic – Daily Telegraph

Ancient Elephant Ancestor Lived in Water, Study Finds – National Geographic

Ancient elephants loved water – LiveScience

Image: courtesy Luci Betti-Nash / Stony Brook University.