An international team of paleontologists headed by Prof. Mark Purnell of the University of Leicester, UK, and Dr. Yuan Wang from the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, China, undertook cutting-edge analysis of fossilized elephant teeth.
Illustration of elephant feeding ecology in the Late Pleistocene of southern China. Elephas (left) incoporates more graze in its diet; whereas Stegodon (right) is an obligate browser of fresh shoots and leaves. Image credit: Nicola Heath.
“We are talking about huge, brick-sized molars here – the largest of any animal, but the signs of tooth wear are tiny, down to thousandths of a millimeter. However, these microscopic surface textures can tell us whether they were eating grass or leaves,” said team member Zhang Hanwen, from the University of Bristol, UK.
By comparing the results with information from modern ruminants (deer, antelopes and oxen) of known diet, the study concluded two extinct elephant genera from southern China – Sinomastodon and Stegodon – were primarily browsing on leaves.
The third, Elephas, which includes the modern Asian elephants, shows much more catholic feeding habit, incorporating both grazing and browsing.
“It’s wonderful that we can identify diets of any fossil mammal with confidence now,” said team member Prof. Christine Janis, also from the University of Bristol.
Sinomastodon and Stegodon coexisted in southern China between 2.6 and 1 million years ago, but Sinomastodon then became extinct and left Stegodon to become the dominant elephant of southern China for the remainder of the Pleistocene, the time of the great Ice Ages.
“The fossil pollen record, and recently-excavated mammal fossil assemblages from various karst cave sites near the Chinese-Vietnamese border, suggest a prolonged, fluctuating period of environmental deterioration around this time,” Hanwen said.
“Forests were on the decline, alongside many of the more archaic mammal species that inhabited them.”
“The highly evolved molars of Stegodon, with multiple enamel ridges, might have allowed it to browse on its preferred foliage in a more efficient way, thus outcompeting Sinomastodon, which preferred the same diet, but had less sophisticated molars consisting of large, blunt, conical cusps.”
On the other hand, the study also suggests that Stegodon and Elephas subsequently coexisted for long periods in southern China by eating different things.
Stegodon remained a specialist foliage feeder whereas Elephas was more of a generalist, consuming a wider variety of vegetation.
Stegodon became extinct at around 11,000 years ago, at the end of the Pleistocene, coinciding with the worldwide disappearance of large mammal species at this time, including the woolly mammoths, giant deers and saber-toothed cats.
The Asian elephant survived in southern China into historical times.
The team’s findings were published online in the journal Quaternary International on July 26, 2016.
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Hanwen Zhang et al. An examination of feeding ecology in Pleistocene proboscideans from southern China (Sinomastodon, Stegodon, Elephas), by means of dental microwear texture analysis. Quaternary International, published online July 26, 2016; doi: 10.1016/j.quaint.2016.07.011
