AsianScientist (Apr. 6, 2016) – A team led by Professor Ao Hong from the Institute of Earth Environment, Chinese Academy of Sciences, has provided age estimates of a Stegodon fossil found in the Lanzhou Basin, clearing up the question of whether it originated in Asia or Africa. Their work was published in Earth and Planetary Science Letters.
The Stegodon is an elephant-like proboscidean that was fairly common across Asia during the Plio-Pleistocene era. It appeared during the late Miocene. The last representatives of the Stegodon disappeared in Indonesia in southeastern Asia at the end of the Pleistocene about 12,000 years ago.
The traditional view is that the Stegodon originated in Asia during the latest Miocene; a competing hypothesis is that this genus dispersed into Asia from Africa. The latter hypothesis is supported by a fossil Stegodon from Kenya, which currently represents the oldest known Stegodon record.
If the traditional view is correct, then there should be Stegodon finds in Asia older than that in Kenya. Until now, however, the oldest evidence of Stegodons in Asia is from the upper Mahui Formation, Yushe Basin, northwest China.
Recently, researchers found another Stegodon fossil in the Xingjiawan Fauna from the Lanzhou Basin, which is located on the northeastern margin of the Tibetan Plateau.
Magnetochronological test results give the fossil an estimated age of at least eight million years, or up to 11 million years. Both age estimations imply that the fossil they found is the oldest known record of the Stegodon worldwide; it predates the former oldest Stegodon find from Africa by at least one million years and perhaps as many as four million years.
This provides new evidence for an Asian origin—specifically from northwest China—for the Stegodon. If it did originate from the northeastern margin of the Tibetan Plateau, where the Lanzhou Basin sits, it could have then dispersed to the Yushe Basin and to Africa in the latest Miocene.
The presence of fossil elephants (e.g. Stegodon) and rhinoceroses (e.g. Chilotherium haberei) in the Basin contrast with the sparse vegetation and absence of these animals and forests today. This implies that the Basin was probably warmer and more humid, with much denser vegetation during the Late Miocene than today, in order to support large mammals such as rhinoceroses, elephants and other browsing mammals.
The article can be found at: Ao et al. (2016) New Magnetochronology of Late Miocene Mammal Fauna, NE Tibetan Plateau, China: Mammal Migration and Paleoenvironments.
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Source: Chinese Academy of Sciences; Photo: Shutterstock.
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