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Paleo Slide Set: Packrat Middens: Vegetation & Climate Variability in the Southwestern United States
Pleistocene midden from Burro Canyon, Kofa Mountains, Yuma County, Arizona
Plant remains are both abundant and well preserved in packrat middens, such as needles (leaves) of a singleleaf piņon (Pinus monophylla,) clearly visible in this 12,000 year-old sample from the Kofa Mountains, 200 km west of Phoenix, Arizona. Open piñon-juniper-oak woodlands occurred at this Sonoran Desert site during the last ice age. The preservation of plant remains in such middens is remarkable, even at the molecular level, allowing a variety of morphological, geochemical and genetic studies. Researchers are working to use polymerase chain reaction (PCR) techniques to extract, amplify and sequence ancient DNA from plant remains found in middens. Such DNA "fingerprinting" can be used to confirm species identifications based on leaf morphology, to identify hybrid zones, and to determine if changes in genotype frequencies accompanied large-scale migrations during the last deglaciation.

Photo Credits:
Thomas R. Van Devender
Arizona Sonora Desert Museum
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Last Modified: 12 October 2001

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