Biogeographic evolution of Equidae

Hyracotherium evolved in North America, and the greatest diverisity of equid fossils is also North American. The "Cone of Diversity" in this conventional portrait of horse evolution implies that Equid diversity has increased steadily over time, whereas it actually depicts only the recent vicariance (dispersal in evolutionary time) of Equus. The genus reached South America, Asia, and Africa (zebras) only very recently, but died out everywhere except the Old World. Horses were re-introduced into North America by Europeans in the 16th century. 

Text material © 2005 by Steven M. Carr