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Show Jack M. Broughton, Department of Anthropology University of Utah Salt Lake City, Utah, 84112 THE HOMESTEAD CAVE ICHTHYOFAUNA: IMPLICATIONS FOR LATE PLEISTOCENE LAKE LEVEL FLUCTUATIONS AND FISH BIOGEOGRAPHY IN THE BONNEVILLE BASIN A faunal record spanning the past 12,000 years was recendy obtained from stratified deposits at Homestead Cave, Lakeside Mountains, Utah. The deepest stratum of this deposit, Stratum I, provided a substantial fish fauna; seven radiocarbon dates derived from Neotoma fecal pellets and yellow- bellied marmot ( Marmotaflaviventris) bone protein bracket the deposition of this stratum between 10,160 and 11,270 radiocarbon years B. P. This collection represents the largest, best preserved, and most precisely dated late Pleistocene ichthyofauna from the Bonneville Basin. The nature of the sediments from Stratum I suggest this fauna was derived largely from raptors, especially owls. Over 3000 fish specimens, representing eight species, have been identified in ongoing analyses of the Stratum I ichthyofauna. The species represented thus far can be divided into two broad groups according to their modern ecological adaptations: 1) those that are more or less obligate to oligotrophia high- elevation, cold, deep water lakes, such as Bonneville cisco ( Prosopium gemmifer), Bonneville whitefish ( Prosopium spilonotus), and Bear Lake sculpin ( Cottus extensus), and 2) those that tolerate a diversity of habitat types, such as Utah chub ( Gila atraria), Utah sucker ( Catostomus ardens), and cutthroat trout ( Oncorhynchus clarki). The species composition of the fishes suggest that during the deposition of Stratum I, the lake was a deep, fresh, and cold, oligotrophic body of water similar to modern high elevation lakes that are fed by mountain glaciers and snowfields. Bear Lake in northeastern Utah- southeastern Idaho, in which three of the represented species are now endemic, is perhaps the best local modern analog. Analyses of Sr/^ Sr ratios from the Homestead Cave fishes have been conducted to inform on the nature of the lake during the time that they were deposited. The ^ Sr/^ Sr ratio of Lake Bonneville varied through time with changes in the elevation of the lake. This was due to changes in the proportional contribution of water from the main input rivers that exhibit distinct8 Sr/^ Sr ratios. Fish vertebrae from Homestead Cave yield very high 87Sr/ 86Sr ratios ( 0.71256- 0.71278), suggesting they were derived from a low- elevation lake similar to, although slightly lower than, Lake Gilbert. Considering the contrast between the elevation of the lake indicated by the 87Sr/ 86Sr ratios and that suggested by the species composition of ichthyofauna, as well as the circumstances under which owls prey upon fish, the Homestead Cave fishes were likely derived from a massive die- off associated with a regressive phase of Lake Bonneville. Analyses of the species composition from upper and lower arbitrarily defined divisions within Stratum I provide further insights into the changes in the nature of Lake Bonneville during the final years of its existence. |
