Lateral trends in carbon isotope ratios reveal a Miocene vegetation gradient in the Siwaliks of Pakistan
- Michèle E. Morgan1,
- Anna K. Behrensmeyer2,
- Catherine Badgley3,
- John C. Barry1,
- Sherry Nelson4 and
- David Pilbeam1
- 1Peabody Museum, Harvard University, Cambridge, Massachusetts 02138, USA
- 2Department of Paleobiology, MRC 121, Smithsonian Institution, P.O. Box 37012, Washington, D.C. 20013-7012, USA
- 3Museum of Paleontology and Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan 48019, USA
- 4Department of Anthropology, University of New Mexico, Albuquerque, New Mexico 87131, USA
Abstract
Isotopic analyses of mammalian tooth enamel from a well-defined, laterally extensive 150 k.y. interval (9.15–9.30 Ma) reveal an ecological gradient in vegetation on the late Miocene sub-Himalayan alluvial plain. Two contemporaneous river systems deposited the sediments of this interval, with a mountain-sourced system (herein, Blue-gray) to the southwest interfingering with a foothill-sourced system (Buff) to the northeast. Fossil mammal teeth collected from a 32 km transect across this fluvial gradient are significantly more depleted in 13C from northeastern localities than from southwestern localities. This trend occurs in equids, giraffids, suids, sivapithecine hominoids, and anthracotheres. We propose that the Buff fluvial system provided more equably moist substrate conditions and supported more closed-canopy vegetation than the Blue-gray fluvial system. Herbivores living along the paleovegetation gradient thus acquired different carbon isotopic signatures during the period of tooth enamel formation, resulting from higher δ13C values in the forage supported by the Blue-gray fluvial system compared with forage associated with the Buff system. The data also imply that many Siwalik mammalian herbivores displayed marked fidelity in juvenile home ranges and habitats.
Footnotes
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↵1 GSA Data Repository item 2009030, Table DR1 (Siwalik U-level mammalian isotopic and locality data) and Table DR2 (specimen counts for large herbivore taxa from the U-level), is available online at www.geosociety.org/pubs/ft2009.htm, or on request from editing{at}geosociety.org or Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301, USA.
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- Received 16 July 2008.
- Revision received 3 October 2008.
- Accepted 3 October 2008.
- © 2009 Geological Society of America
