Did elephants’ trunks evolve to function as snorkels? This suggestion might be outlandish but new fossils make a strong case that extinct relatives of elephants were aquatic.

Speculation about a watery stage in the evolution of the world’s largest land mammal has continued on and off for years, but now palaeontologists have solid evidence that relatives of elephants lived in freshwater swamps or rivers near the coast of what is now Egypt.

Elwyn Simons of Duke University in North Carolina and colleagues analysed the teeth of Moeritherium, an elephant ancestor the size of a large hog that lived 37 million years ago. The teeth have uniformly low levels of oxygen-18, a distinctive signature of organisms that live in fresh water. And their carbon-13 levels indicate that the animal ate freshwater plants.

Oxygen and carbon isotope levels are similar in the teeth of Barytherium, a much larger but poorly known beast more closely related to modern elephants.


No connection

Simons says that the results suggest that the ancestors of modern elephants went through an aquatic or semi-aquatic stage before going back to the land.

William Sanders of the University of Michigan agrees that both Moeritherium and Barytherium were aquatic but says neither was on the direct line to elephants.

He also dismissed the “trunk-as-snorkel” hypothesis, arguing that trunks grew long to reach beyond the elephants’ tusks. He doubts that purely aquatic traits would have remained long after ancestral forms left the water.

Paleomastodons, which are direct ancestors of elephants, were fully terrestrial when they appeared around 30 million years ago, but no one knows what their ancestors were or what they were doing. Simons hopes that isotopic studies of other fossils might provide the answer.

Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0800884105)

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