Spatial and temporal variations in the isotopic composition of bison toothenamel from the Early Holocene Hudson-Meng Bone Bed, Nebraska

The Hudson-Meng bone bed in northwestern Nebraska is an early Holocene depo sit of hundreds of bison of differing ages that were killed in a catastroph ic event of unknown origin. The M-1, M-2, and M-3 molars of individuals, ra nging from ca. 1 to 7 years of age at the time of their death, were examine d to determine inter- and intra-tooth isotopic variability, and to link thi s variability to time in order to better understand the environments that e xisted prior to the mass death event. The delta(13)C value of molar structu ral carbonate increases by 2-3 parts per thousand from the M-1 to M-3 molar s, reflecting increasing direct forage signals, and decreasing maternal inf luences. The delta(18)O value of molar structural carbonate in a given indi vidual shows no consistent trend with time from birth, indicating a fairly direct linkage to 'dietary water' regardless of tooth ontogeny. Detailed 'd own-tooth' isotopic measurements indicate a small seasonal signal in the de lta(13)C value of forage/maternal milk, which appeared to have been largely dominated by C-4 flora. In contrast. there was almost a 10 parts per thous and range in the isotopic composition of dietary water, a range that is wit hin present-day summer versus winter precipitation in the region. The delta (18)O value of bulk tooth enamel, arranged by approximate time prior to the death event, indicate a consistent increase in the delta(18)O value of bod y water (2-3 parts per thousand), suggesting a long-term decrease in winter /spring precipitation and/or drought. The delta(18)O trend with time, coupl ed with the high C-4 grass abundance, suggest environmental stresses on thp herd preceding the catastrophic death event. (C) 2000 Elsevier Science B.V . All rights reserved.