Is it possible to recognize a biotic unit between North and South America?

There are differences in the biotic delimitation and recognition of the central part of the Americas, specifically from southern Mexico to northern South America. The delimitation of this area has been difficult when typical characteristics, product of patterns of distribution of the species, and diagnostic criteria are considered in its identification. This study present different arguments about the existence of a biotic Mesoamerica trough the biogeographical knowledge, which can help in its recognition and its differences from neighboring areas by biotic gradients. Some criteria have been considered and the problems present in the understanding of the region have been discussed.