Moeritherium, a 37 million-year-old amphibious relative of elephants
The evidence that the ancient relative of today's elephants lived in fresh water is published today by an international team led by an Oxford University scientist.
The scientists were investigating the lifestyle of the two early elephants - called proboscideans - Moeritherium ('the beast from Lake Moeris') and Barytherium, which looked like a slender version of today's Asian elephant - that lived over 37 million years ago in what today is Egypt's Fayum Desert.
By analysing isotopes in tooth enamel from Moeritherium - a creature a little larger than a pygmy hippo with a prehensile upper lip, like that of a tapir, rather than a full blown trunk - they were able to deduce that it was very likely a semi-aquatic mammal, spending its days in water eating freshwater plants when the region was much wetter and lusher than today.
'We know from molecular data that modern elephants share a common ancestry with the sirenians - aquatic sea cows and dugongs', said Alexander Liu of Oxford's Department of Earth Sciences, lead author of a report published in the Proceedings of the National Academy of Sciences.
The genetic evidence strongly suggested that elephants may have an ancestor which was amphibious in its mode of life and "we wanted to know if Moeritherium or Barytherium was this semi-aquatic ancient relative.
Unfortunately only few remains of the skeletons of these early elephants survive, so instead of looking at their bones we looked at the chemical composition of their teeth to determine what they ate and how they lived'.
Mr Liu, with colleagues Erik Seiffert from Stony Brook University and Elwyn Simons from the Duke Lemur Centre, both in America, analysed the oxygen and carbon isotope ratios contained within tooth enamel.
While carbon isotopes can give clues as to an animal's diet, oxygen isotopes found in teeth come from local water sources, and their variability in mammal populations can give an indication of the type of environment the animals lived in, in this case showing that Moeritherium was semi-aquatic. The results for Barytherium were ambiguous but do not rule out it being another swamp lover.
Mr Liu adds: 'We now have substantial evidence to suggest that modern elephants do have ancient relatives which lived primarily in water. The next steps are to conduct similar analyses on other elephant ancestors to determine when the switch from water to land occurred'.