Late Pleistocene to Late Holocene variability in bison health: Implications for human bison-based subsistence on the Northwestern and Central Great Plains
This dissertation explores how evolutionary trends in bison health potentially influenced the nutrient acquisition strategies of Northwestern and Central Great Plains bison hunters from the Late Pleistocene to Late Holocene. Some models, based on skeletal evidence of diachronic variability in the nature and scale of bison carcass processing at kill-butcheries, maintain that declining bison health through the Holocene was one major factor that prompted hunter-gatherers to intensify processing behaviors over time, particularly those related to long bone marrow fat extraction. However, this hypothesis has never been adequately tested and this investigation seeks to do so.
Here, variability in bison health, representing a hierarchical gradient reflecting short term changes in individual condition and longer term deviations in individual fitness and population-level health, are measured using a suite of dento-mandibular paleopathologies including enamel hypoplasia, enamel structural damage (e.g., enamel spalling), molar malformation, abnormal tooth wear, and mandibular infection (e.g., lumpy jaw). Research suggests that enamel hypoplasia probably best represents short term (i.e., intra-annual) variability in individual bison condition, while longer term (i.e., inter-annual, decadal) changes are conversely better reflected by pathologies that directly affect mastication efficiency, such as enamel spalling and lumpy jaw.
Analyses of 3,186 mandibular dentaries, representing 910 individual bison from 23 modern, archaeological, and paleontological Northwestern and Central Great Plains (i.e., Montana, Wyoming, Nebraska, and Colorado) assemblages indicate that while Late Pleistocene and Early Holocene populations retain significant numbers of specimens bearing enamel hypoplasia, there is no significant inter-population or inter-period difference in deformation timing, implying that intra-annual fluctuations in bison condition remained constant over at least the last eleven thousand years. Enamel spalling and mandibular infection is conversely more abundant among Middle and Late Holocene populations, suggesting that mastication efficiency, and thus long-term trends in fitness and population-level health, was affected most during this time.
Given this, and considering the punctuated diminution of Great Plains bison related to paleoclimate and paleolandscape fluctuations throughout the Holocene, resultant data suggest that Late Holocene bison probably exhibited tighter metabolic controls over body fat content and, in this sense, were indeed in overall poorer health than their Late Pleistocene and Early Holocene progenitors. However, it is uncertain what health affects greater frequencies of enamel hypoplasia, as well as some genetically linked pathologies, had among Late Pleistocene and Early Holocene populations. This uncertainty is compounded by suspicions regarding the cause of hypoplasias identified in this analysis.
Overall, it appears that Holocene variability in bison health was certainly one factor that guided human decisions about nutrient acquisition from bison carcasses through time. However, increasing population densities, expanding trade networks and territoriality were almost certainly equally prominent factors in the evolution of processing behaviors.