Initial plots of appendicular element lengths indicate the female animals from the Upper Kill are larger than females in either of the other two kill levels at Cooper. Radii length from female skeletons older than 2 average 353.3 mm, 340.8 mm, and 338.0 mm for the Upper, Middle, and Lower kills, respectively. The Upper Kill radii are on average 15 mm longer than radii from either of the other kills. Similar size differences are seen in the other long bones. The source of this variation is yet to be determined.
Genetic analysis awaits funding.
The possibility that environmental factors and not genetic factors are at work have been partially explored. The stable isotope analysis provides some indication that the herds killed at Cooper migrated from areas of the plains where grass composition was slightly different. Applying the analytical technique to the bison remains from the Upper and Middle kills at Cooper provide interesting, and somewhat unexpected, results. The Lower kill was omitted from this analysis due to its small sample size. Plots of the ratio of femur length to metatarsal length against age yielded differing regression lines for the Upper and Middle kill animals.