Late Pleistocene northward-dispersing Bison antiquus from the Bighill Creek Formation, Gallelli Gravel Pit, Alberta, Canada, and the fate of Bison occidentalis

Late Pleistocene bison skeletal remains from the Gallelli Gravel Pit in the Bighill Creek Formation at Calgary, Alberta, document at least two individuals, including the largest postglacial bison reported from North America south of Beringia. Two partial crania, dated to 11 290 and 10 100 C-14 years BP, are referred to the southern species Bison antiquus Leidy, indicating northward movement from the midcontinent as ice retreat opened a corridor between Laurentide and Cordilleran ice. Their large size suggests a dispersal phenotype exploiting newly available territory. DNA evidence links the 11 290-year-old bison to Clade 1, which includes modern B. bison. This supports in situ evolution of B. bison from B. antiquus through the intermediate usually called B. occidentalis''. Bison of B. occidentalis'' character appeared in Alberta about 10 ka BP, and the DNA evidence counters the suggestion of a migratory wave from Beringia. The B. occidentalis type specimen is from Alaska, so this name may be inappropriate for southern populations. Radiocarbon dates suggest that the Bighill Creek Formation paleofauna comprises two faunules separated in time by the Younger Dryas climatic episode.