Most mammals do not wander: few species escape continental endemism

Terrestrial mammals are found nearly everywhere on Earth. Yet, most taxa are endemic to a single continent; geological, evolutionary, ecological, or physiological filters constrain geographic distributions. Here, we synthesize data on geography, taxonomy, lineage age, dispersal, body size, and diet for > 4000 terrestrial mammals prior to detectable human‐mediated biodiversity losses and quantify factors correlated with the likelihood of dispersal between continents. We confirm the uniqueness of being on multiple continents: excluding humans and commensals, only 260 mammals are found on two continents, while six span three or more continents (the red deer, red fox, brown bear, least weasel, and common bent‐wing bat), and just a single species – the lion – once had a geographic range that included four continents. Clearly the challenges of colonizing and persisting on multiple continents are severe. No single characteristic enables taxa to be on more than one continent. Rather, a suite of prerequisite conditions under some circumstances lead to distributions spanning multiple continents. The suite of factors facilitating the occupation of two continents, like being volant, are distinct from those that lead to the occupation of three or more, which are primarily faunivores. Other than humans and our commensals, very few species have become truly cosmopolitan over evolutionary time and geographic space.