HR: 14:55h
AN: B53B-06    [Abstracts]
TI: Preliminary Radiocarbon Chronology and Paleoecological Analysis of the Small Mammals in Samwel and Potter Creek Caves, Shasta County, California, and its Relation to the End-Pleistocene Extinction
AU: * Feranec, R S
EM: feranec@stanford.edu
AF: Stanford University, Department of Biological Sciences, Stanford, CA 94305 United States
AU: Blois, J L
EM: jblois@stanford.edu
AF: Stanford University, Department of Biological Sciences, Stanford, CA 94305 United States
AU: Hadly, E A
EM: hadly@stanford.edu
AF: Stanford University, Department of Biological Sciences, Stanford, CA 94305 United States
AB: Although mostly excavated before 1910, the fossil deposits discovered in Samwel and Potter Creek Caves in northern California have been little studied. The deposits within the caves have yielded both extinct megafauna and archaeological remains implying that the deposits cross the Pleistocene-Holocene transition. Small mammals are abundant within these cave deposits, and many of these smaller mammals are from extant species of California, survivors of the end Pleistocene extinction. Because of the abundant fossils collected in stratigraphic context, our ultimate goal is the use these unique sites to assess community and population response of the extant mammals to the end Pleistocene event. However, our initial aim was to answer the following two questions regarding the small mammal communities: (1) What is the chronology of the small mammals in the cave deposits? (2) Are ecological changes occurring within the small mammal taxa? To determine chronology, we prepared 10 small mammal samples for radiocarbon analysis using standard techniques. The samples were analyzed and dated at the Lawrence Livermore National Laboratory. Our dates, selected from across the strata, ranged from 1,200 to 21,000 radiocarbon years before present. For a preliminary assessment of ecological changes through time, we used cranial metrics of ground squirrels ( Spermophilus sp.). Diastemal length (the distance between the first molariform tooth and incisor) is an index of body size, which is a function of the physiology of the individual. Toothrow measures the length of the molariform teeth, and does not change with the ontogeny of the individual, but can represent heritable, evolutionary changes in size or species replacement. Our preliminary results are promising, demonstrating a significant decrease in diastemal length, or ecophenotypic body size, at the top of the deposit. No significant change was observed in toothrow length. Our results confirm that the deposits of these northern California caves do span the Pleistocene-Holocene boundary. This transition is associated with our preliminary results from ground squirrels showing no species replacement and a reduction in body size. Body size reduction is an expected outcome of warming at the end Pleistocene, but future research will address mechanism directly in this and other small mammal species.
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0444 Evolutionary geobiology
DE: 0459 Macro- and micropaleontology (3030, 4944)
DE: 1105 Quaternary geochronology
DE: 1115 Radioisotope geochronology
SC: Biogeosciences [B]
MN: Fall Meeting 2005