Evolutionary adaptation in the Spanish Anchitheriinae in relation to environmental and climatic changes

Abstract

The Anchitheriinae are an extinct subfamily of Equidae that first appeared in North America near the base of the Miocene. The Anchitheriinae clade migrated via Asia to Europe and has its first occurrences in Europe during the middle Orleanian, MN 3. The entire genus became extinct in the Vallesian, MN 9. Anchitheriinae have generally been considered to be browsing horses that occupied forested habitats because of their low crowned, lophodont teeth (Forsten 1991, Janis 1995). One of the classic examples of faunal turnover in the fossil record is the Late Miocene transition from faunas dominated by Anchitheriinae with low crowned molar teeth to faunas with Hipparion horses characterized by high-crowned teeth (Eronen et al. 2009, Strömberg 2005). This spread of Hipparion horses is often associated with the expansion of open habitats and also the increase of C4 grasses. It is generally accepted that Anchitheriine horses did not display an evolutionary increase in tooth crown height prior to their extinction (Eronen et al. 2009). “Lineages that remained as browsers in the Mid Miocene did not later transform into grazers, the general evolutionary pattern in the late Miocene is for browsing lineages to be replaced by ones adapted to more fibrous diets rather than the browsers themselves undergoing evolutionary change” (Janis 1994). Recent research on Anchitherium teeth as well as body size and isotopic composition of their dentition has shown however that adaptations to the overall changing environments in Europe as well as to a changing local climate and vegetation may have occurred in the Anchitheriine genus after all (Forsten 1991, Eronen et al. 2009, Kaiser 2009).