Paleomastozoology of the San Miguel de Allende basin, State of Guanajuato, its Contributions: The Biotic Exchange between the Americas

Abstract

In the San Miguel Allende basin there is the most complete stratigraphic sequence of the late Tertiary known in Mexico and possibly in North America. It is the only research area where, until now, two ages of mammals are superimposed, Henfilian (Late Miocene-Pliocene) and Blancan (Pliocene), which contain the most complete information on the diversity of mammal faunas of the Tertiary-River, late in the basins of the Trans-Mexican Volcanic Belt. The South American immigrants present in the faunas of the San Miguel Allende basin are at least one million years older than those described in the faunas of North America, which suggests that the Panamanian Bridge that allowed the passage of immigrants between the Americas, was efficient in the limits of the Henfiliano-Blancano, more than a million years earlier than suggested by the findings of these immigrants in the faunas of Arizona, Texas and Florida According to the information available, it is possible to infer that there were different migration periods possibly due to differences in sea level or tectonic movements that limited the efficiency of the Panamanian bridge, which was established during the Irvingtonian, opening the route of reciprocal exchange of fauna between the Americas.