Figure 2.

North American continent-wide ungulate generic diversity. H, hypsodont genera; M, mesodont genera; B, brachydont genera. For reference, the time range of the C₃/C₄ transition (11) is marked by the vertical bar. Hypsodont taxa are here interpreted as either grazers or open-habitat mixed feeders; mesodont taxa as mixed feeders of all types (and possibly including some true grazers); and brachydont taxa as browsers, based on study of diets and crown heights of modern species (18, 20). Generic data are from ref. 13.