Patterns of Old World Hipparionine Evolutionary Diversification and Biogeographic Extension

Hipparionine horses have long been united evolutionarily by the presence of three toes per digit, having high crowned cheek teeth with cement, and isolated proto-cones on upper cheek teeth (Christol, 1832). Geochronologically they have further been recognized as the preeminent large mammal “index” fossils for late Neogene Old World deposits. Their abundance in later Neogene mammal faunas has prompted the production of a staggering body of systematic and interpretive literature during the last 150 years. In the last 40 years there has been an increasing number of attempts to reorganize parts of Old World hipparionine systematics by regional studies of variable scope including Europe in gener…