What characteristics predispose mammals to be successful migrants? Is there an optimal body size or ecological specialization that facilitates the movement of species across space? Here, using a global database of mammals, we examine the overlap in species distributions across the five major continents (North America, South America, Eurasia, Africa and Australia). We include late Quaternary and both volant and nonvolant mammals, but exclude humans and anthropogenic-mediated introductions. 
Results/Conclusions

Interestingly, less than 5% of the species present in the late Quaternary are found on more than one continent, and only four species have distributions that include three continents; no non-introduced mammal is found on all continents except humans. Given the very low taxonomic overlap in shared species, we discuss the roles that body size, ecology, phylogeny, and geology play in driving observed continental species distributions.