April 15, 2008 -- Fossils of two ancient, extinct mammals are helping piece together the elephant family tree.
Modern elephants and their relatives, which fall into the order Proboscidea, form a diverse clan that includes hyraxes, manatees and dugongs. That group can now be linked to two extinct beasts, known as Barytherium and Moeritherium, which emerged around 50 million years ago.
Surprisingly, they didn't look much like elephants or their living relatives either.
According to Alexander Liu, lead researcher on a new study of the fossils, Moeritherium was much smaller than today's elephants and was instead "similar in size and stature to a modern tapir, having a prehensile upper lip rather than a trunk and weighing roughly 250 to 300 kg (551 to 661 pounds)."
Modern elephants, by contrast, can weigh up to 24,000 pounds.
Barytherium, on the other hand, was a little more elephant-like, given its trunk, but was still much smaller than today's elephants, Liu told Discovery News.
Liu, a researcher in the University of Oxford's Department of Earth Sciences, along with colleagues Erik Seiffert and Elwyn Simons, reconstructed the habitats and behaviors of the two extinct animals just by analyzing 11 of the beasts' teeth.
Their findings are published in the latest issue of Proceedings of the National Academy of Sciences.
Their detective work involved studying carbon and oxygen isotopes found in the teeth, which date to 37 million years ago and were excavated at the Birket Qarun Formation in northern Egypt. Isotopes are forms of chemical elements that possess different numbers of neutrons, or atomic weights. Over time, they leave behind detectable signatures.
Carbon, for example, is a building block of vegetation, so carbon isotopes within tooth enamel can reveal the basic types of food that the individual ate. In this case, the researchers found that both Moeritherium and Barytherium consumed mostly freshwater plants, with Barytherium also possibly eating terrestrial plants.
The oxygen isotopes suggest Moeritherium lived in shallow tropical rivers or swamps and that Barytherium was probably a semi-aquatic creature.
The new findings, combined with prior molecular data, suggest that the two extinct animals were indeed relatives of elephants, manatees, dugongs and hyraxes -- which are perhaps the most unlikely members of the group, given their diminutive, furry bodies.
"You have to remember that although modern hyraxes are small and cute, in the Eocene they were the dominant terrestrial herbivore in the Fayum (Egyptian) region, with a lot of diversity in size and shape," said Liu.
"It is possible to excavate hyrax skulls that are themselves the size of modern hyraxes, and some hyracoids could easily have rivaled Moeritherium in size," he added.
Liu speculates that a drought ended the ancient animals' tropical existence. Elephants and hyraxes might have later been pushed into more terrestrial habitats, while dugongs and manatees might have already become adapted to salt water.
University of Michigan paleontologist Bill Sanders told Discovery News that he found the isotope analysis to be "first-class work, with very clever and convincing interpretations to confirm that these proboscideans were likely to have been semi aquatic."
Sanders, however, questioned the relevance of such ancient elephant relatives, since modern elephants only first appeared 7 million years ago.
"Nearly all of the proboscideans that lived in the intervening time between moeritheres and elephants were terrestrial," he said, adding that the Egyptian site of the teeth finds might also have affected the findings, since other early elephant relatives could have lived in less water-dominant environments.
Despite these reservations, Sanders believes the new research "sets a good framework" for additional studies on the elephant family tree. He hopes Liu and his team will study remains from other elephant relatives, such as Phosphatherium and Numidotherium, in the future.
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