Valsequillo biostratigraphy II. Bison, tools, correlate with Tequixquiac

The controversial Paleoindian FAD (first appearance date) has been complicated at Valsequillo by some erratic U-series dates which contradict conventional 14 C dates and tool typology. Biostratigraphic correlation with a more precise Bison FAD, shows the relevance of paleontology in prehistoric reconstruction. The LAD (last appearance date) of medium-sized Bison chaneyi, 26,820 ± 350 yr B.P., and the FAD o short-horned B antiquus 22,130 ± 350 yr B.P., indicate that species replacement was around 30,000 yr B.P. B. antiquus occurs at Tequixquiac, Upper Becerra, and Valsequillo, Fauna Zone II, av. date 23.000 yr B.P., Mexico. Unifacial edge-trimmed tools occur at the base of the Upper Becerra, Tequixquiac, in the level with B. chaneyi, and unifacial tools occur in the Faunal Zone II, Valsequillo, at the level with B. antiquus. Both sites are isochrons of fossil soil fB01 with minimum date of 23,980 ± 1000 yr B.P. at Malinche volcano in Puebla and traced westward over the Sierra Nevada into the Valley of Mexico. This supports the conclusion that the Central Mexico Paleoindian sites represent the earliest documented FAD.