STASIS IN THE LATE PLEISTOCENE GROUND SLOTHS (PARAMYLODON HARLANI) FROM RANCHO LA BREA TAR PITS, CALIFORNIA

Stasis in Pleistocene mammals in the face of climatic change during the glacial-interglacial cycles hasbeen widely documented. We examined the size and shape changes of the bones of common large ground sloth,Paramylodon harlani, from Rancho La Brea. We measured multiple dimensions of most the adult unbrokenastragali, patellae, and the major limb bones; only the astragali, patella, and radii were abundant in enough welldated pits for analysis. In every dimension, these bones show stasis in linear dimensions, as well as in robustnessof limb elements. Statistical analysis by ANOVA confirmed that the means of all the temporally sequential sampleswere not significantly different from each other, so stasis prevails. These results, together with those of everycommon large bird or mammal from Rancho La Brea, show that stasis prevailed in the region from 35,000 to 11,000years ago, despite climate changes that caused the region to go from oak-chaparral at 35 ka, to closed-cone snowypiñon-juniper forest at peak glacial 21 ka, and then back to oak-chaparral-sage scrub vegetation over the past10,000 years.