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The Quaternary Times
Newsletter of the American Quaternary Association
Volume 29 Number 1 May 1999

Quaternary Paleobiology Update
Debate continues over the cause of Pleistocene megafauna extinction

One of the topics in Quaternary paleobiology that has been back in the news lately is the question of the megafaunal mammal extinction event at the end of the last glaciation. Gifford Miller (INSTAAR and Dept. of Geological Sciences, University of Colorado) worked with John Magee and other colleagues at the Australian National University to date the extinction of a Pleistocene flightless bird in Australia (Miller et al., 1999). As in North America, nearly all of the Australian megafauna (terrestrial animals with body mass greater than 44 kg) became extinct in the Late Pleistocene. Most of these were marsupial mammals, but Genyornis newtoni, a large flightless bird, also became extinct. Miller and his colleagues obtained more than 700 dates (amino acid racemization, AMS radiocarbon, and TIMS) on the fossil eggshell fragments of this species. The bird died out 50,000 years ago, during an interval of relatively modest climatic change. Miller et al. argue that this extinction was caused by human predation; humans entered Australia at approximately the same time as the birds disappeared from the fossil record.
Meanwhile, in North America the debate on megafaunal mammal extinction is about to get a much-needed injection of reliable data. Paleontologists Holmes Semken (University of Iowa) and Russell Graham (Denver Museum of Natural History), and radiocarbon dating expert Tom Stafford (Stafford Research Laboratory, Boulder, Colorado) have obtained 140 new AMS dates on proteins extracted from fossil bones of megafaunal mammals that died near the end of the last glaciation. The bones come mainly from North American sites, from Alaska to Mexico. The results of this new study are quite startling. It now appears that the major megafaunal exinction event took place at 11,400 14C yr B.P. This event included the extinction of camels, horses, giant sloths, Pleistocene bison, and all other genera of megafaunal mammals that did not survive beyond 11,400 14C yr B.P. , with the exception of the proboscideans. Mammoths and mastodons persisted beyond 11,400 yr B.P. Stafford et al. have dated the extinction of North American mammoth and mastodon to 10,900-10,850 yr B.P. So it now appears that there were two distinct extinction episodes. Each event took less than 100 years.
The older event may have taken place before, during, or just after the first appearance of Clovis artifacts in the archaeological record. The most recent evaluation of the age of Clovis sites in North America (Taylor et al., 1996) places the beginning of this culture at 11,500 yr B.P. If the people who used Clovis tools arrived in North America at that time, then they have never seen most of the Pleistocene megafaunal mammal species, much less have been responsible for their demise. There is good evidence that Clovis hunters killed and butchered mammoth and mastodon, the megafaunal species that died out a few centuries later. Whether human predation was responsible for the proboscidean extinction remains an open question.
Several scenarios suggest themselves concerning the earlier (11,400 yr B.P.) extinction event. In one scenario (fitting the "Clovis first" paradigm), people had little or nothing to do with the extinction of most of the Pleistocene megafauna. In another scenario (fitting the "pre-Clovis occupation" paradigm), Paleoindians who lived in North America before 11,500 yr B.P. were responsible for the demise of the megafauna, even though the evidence for their occupation is spotty at best. In a third scenario (fitting the paradigm that Paleoindians lived in harmony with nature and did not drive any other species to extinction), the megafaunal extinction had little or nothing to do with human predation, be it the Clovis culture or otherwise. The debate will certainly continue, but the new radiocarbon ages that date the extinction events are an important contribution to a discussion that generally suffers from a lack of hard data.

References cited
Miller, G. H., Magee, J. W., Johnson, B. J., Fogel, M. L., Spooner, N. A., McCulloch, M. T., and Ayliffe, L. K. (1999). Pleistocene extinction of Genyornis newtoni: human impact on Australian megafauna. Science 283, 205-208.

Taylor, R.E., Haynes C. V., Jr., and Stuiver, M. (1996). Clovis and Folsom age estimates: stratigraphic context and radiocarbon calibration. Antiquity, 70, 515-525.
Scott A. Elias
AMQUA Paleobiology Councilor
Institute of Arctic and Alpine Research
University of Colorado