The Eocene represents a special period in the history of carnivores, a point of equilibrium between two possibilities, one of which is realized and the other now forgotten. Mammals were not the only candidates for success: a gigantic (over two meters tall) Eocene predatory bird found in Wyoming, Diatryma gigantea, tells a different story. The sceptre of dominant carnivores could have gone to birds, but it went to mammals, for no known reason. In South America, for example, predatory birds prevailed until the closure of the Isthmus of Panama.
