RECONSTRUCTING CAVE BEAR PALEOECOLOGY FROM SKELETONS - A CROSS-DISCIPLINARY STUDY OF MIDDLE PLEISTOCENE BEARS FROM YARIMBURGAZ CAVE, TURKEY

Cave bears, an extinct subgenus (Spelearctos) of Ursus, were versatile enough to inhabit large areas of the northern hemisphere during the m iddle and late Pleistocene, yet they had evolved a specialized dentiti on that emphasized grinding functions, implying a heavy dietary relian ce on tough, fibrous foods (i.e., plants). Isotope studies have yielde d conflicting results on cave bear diet, however, often without consid eration of the provenance of the samples or the possible contradiction s that taphonomic and morphologic evidence might pose to dietary inter pretations. It is likely that cave bear habits varied somewhat in resp onse to environmental circumstance, and the limits on their abilities to do so remain unknown. If the larger goal of paleontological inquiry is to reconstruct the adaptations of cave bear species, then variatio n and commonalities among populations must be tracked closely and the disparate lines of evidence currently available examined together on a case by case basis. Clearly, no single analytical technique can achie ve this. By way of example we present the results of a cross-disciplin ary collaboration that combines osteometric, isotopic, and taphonomic approaches to studying the paleoecology of a bear assemblage from Yari mburgaz Cave in northwest Turkey. Reference information on the linkage s between diet, hibernation, and population structure in modern bears provides test implications for the investigation. Osteometric techniqu es demonstrate the presence of two coextant middle Pleistocene bear sp ecies in the sample-Ursus (Spelearctos) deningeri, a form of cave bear , and U. arctos or brown bear-the former abundant in the sample, the l atter rare. An attritional mortality pattern for the bears and the con dition of their bones show that most or all of the animals died in the cave from nonviolent causes in the context of hibernation. The study also elucidates several characteristics of the cave bear population in this region. Osteometric techniques show that the adult sex ratio of the cave bears is only slightly skewed toward females. This pattern li es near one extreme of the full range of possible outcomes in modern b ear species and can only reflect a strong dietary dependence on season ally available plants and invertebrates, showing that hibernation was a crucial overwintering strategy for both sexes; the results specifica lly contradict the possibility of regular, heavy emphasis on large gam e (hunted or scavenged) as a winter food source. The nature of wear an d breakage to the adult cave bear teeth indicates that food frequently was obtained from cryptic sources, requiring digging and prying, and that extensive mastication was necessary leading to complete obliterat ion of some cheek tooth crowns in old individuals. The patterns of too th damage during life corroborate the dietary implications of the adul t sex ratio and also argue for a diet rich in tough, abrasive material s such as nuts, tubers, and associated grit. The carbon and oxygen iso topic compositions of cave and brown bear tooth enamel from the site a re virtually identical, and there is no evidence of a strong marine si gnal in either species, despite the cave's proximity to a modern estua ry of the Sea of Marmara; nitrogen isotope ratios could not be examine d because of poor protein preservation. The isotope results suggest th at both bear species were highly omnivorous in the region during the m iddle Pleistocene acid obtained nearly all of their food from terrestr ial and fresh-water habitats. Bone pathologies, usually originating fr om trauma, occur in some of the adult bears, testifying to long lifesp ans of some individuals in this fossil population. The Yarimburgaz cav e bears also exhibit great size dimorphism between the sexes, based on weight-bearing carpal bone dimensions, with adult males attaining rou ghly twice the body mass of adult females.