DID PRONGHORNS BECOME SMALLER AFTER THE ICE AGES?

According to Adams et al. (1999), Holocene pronghorns (Antilocapra americana) reduced in size at the end of the last Ice Age. This conclusion was based on very small samples from the late Pleistocene Natural Trap Cave in Wyoming (17,000-20,000 years BP), the early Holocene (early Plains Archaic culture, about 7000 years BP) Trappers Point site in Wyoming, the Protohistoric (less than 500 years old) Eden-Farson site in Wyoming, and modern samples. We re-examined this claim, adding to the sample the pronghorns from the late Pleistocene deposits at Rancho La Brea tar pits in Los Angeles, mostly from Pit 3 and dated around 18,000 years BP, as well as additional modern pronghorns. We measured the same bones that Adams et al. (1999) reported, as well as other dimensions of the common limb bones. We employed the Kruskal-Wallis test for significance of difference in single variable between non-parametric samples, and Hotelling’s T² test for significance of differences in bivariate data. There is no statistically significant difference between late Pleistocene pronghorns from either La Brea or Natural Trap Cave compared to each other, or to modern samples. Only the early Holocene Trappers Point samples are slightly larger (about 8% larger) than all the remaining samples, and this is not statistically significant. Thus, if pronghorns changed size at all in the last 20,000 years, they increased slightly in the early Holocene, but have reverted to their late Pleistocene size since then.