SIZE AND SHAPE STASIS IN RANCHO LA BREA FELIDS DURING THE LATE PLEISTOCENE: UNIVARIATE AND MULTIVARIATE STATISTICAL APPROACHES

Several authors have claimed that the large felids of North America changed in size and shape through the late Pleistocene. We re-examined the two common felids, the sabertoothed cat Smilodon fatalis, and the American lion, Panthera atrox, from the Rancho La Brea tar pits in the Page Museum in Los Angeles. We measured large samples (typically 30 to 100 specimens of each element) of several dimensions of the most common bones (typically leg or foot bones) from all the pits with good radiocarbon dates. We analyzed the univariate data for significance of differences using ANOVA, and used Principal Components Analysis (PCA) to see if shape changes could be recognized by multivariate analysis of humeri and femora. Even though pollen, plants, snails, and isotopic studies provide evidence of dramatic climatic and vegetational change from the previous interglacial to the Holocene, none of the felids show any statistically significant differences in size or shape of their bones from one level to the next. This was true not only of the univariate data, but also the PCA, since the first PC/ first factor (usually a proxy of size) showed no significant differences from one pit to the next. The first PC/first factor typically accounted for 75% or more of the variation, with the second and third factor only accounting for less than 10% each. These factors showed no consistent loadings on any particular variable, so they gave no significant indication of shape change from 34 ka to 11 ka.