Biogeographic regionalization and biotic evolution of Mexico: biodiversity's crossroads of the New World

Mexico's incredible specific and ecosystemic diversity places it among the megadiverse countries of the planet. The biogeographic patterns exhibited by the taxa of the country also show a remarkable complexity. The northern part of Mexico is located in the Nearctic region, whereas the southernmost part belongs to the Neotropical region. Between both, mainly in the "Sierras Madre" and the Transmexican Volcanic Belt, the mixture of Nearctic and Neotropical taxa constitutes the so-called Mexican Transition Zone. This biotic crossroads makes the diversity of Mexico so interesting, not only in terms of its endemic species, but also in terms of their varied phylogenetic relationships and the hypotheses that have been proposed for explaining how taxa of diverse origins have been assembled in the Mexican Transition Zone. Additionally, the country possesses almost all types of vegetation, with deserts, tropical and temperate forests, grasslands and high mountain wilderness. The biogeographic regionalization of the country is revised, recognizing 2 regions, 1 transition zone, 14 provinces and 42 districts.