Metapodial morphology and the evolutionary transition of Late Pleistocene to modern bison

The evolution of late Quaternary bison has long been debated with various interpretations proposed surrounding the rate, cause, and pattern of morphological change in the lineage. Bison from the Southern Plains, however, have been underrepresented in this debate, as most research has centered on Northern Plains populations. Likewise, interpretations have relied heavily on horn core analysis and related cranial characteristics rather than postcranial elements. The research of this dissertation is centered on an examination of the large sample of bison metapodials from the Lubbock Lake Landmark, Southern High Plains of Texas. The analysis looks at the metapodials of late Quaternary bison and how these elements were changing in respect to size, overall shape, and robusticity (relative cortical bone thickness). Several measurements from metapodials dating to different periods of the late Quaternary are used. The measurements are taken both from the fossils themselves as well as from X-rays of the fossils. These measurements are then examined and tested with univariate and multivariate statistical methods. The impact of these analyses on the issues of bison taxonomy and phylogeny are explored, as are the possible causes for the morphological changes.; Results suggest a single species should be recognized from the late Quaternary, as morphological variation in the late Quaternary bison does not support multiple species. The pattern and rate of morphological change indicate that modern metapodial morphology appeared first on the Southern Plains prior to 6,500 BP and subsequently spread northward. The changes in metapodial morphology do not appear to result from human hunting pressure, as has been suggested, but rather are likely due to dramatic changes in the flora brought about by the warming temperatures and decreasing precipitation of the period. A reduction in stands of trees and the transition from C3 to C4 grasses during the late Quaternary correlate well with morphological changes in the bison lineage.