Previous work by the co-investigators has revealed some critical gaps in our knowledge of relationships among hipparionine (3-toed) horses that must be filled before further work on their evolutionary history can be meaningfully pursued. They now propose to conduct analyses of North American hipparionine quarry samples and related, more primitive "merychippine" species, in order to clarify the evolutionary relationships of all hipparionine horses. This work, coupled with ongoing work on Old World forms, will be important for advancing our knowledge of the 16 million year history of this group. In turn, resolution of relationships in this group will allow us to use it for provincial and intercontinental geological correlations as well as for reconstruction of intercontinental connections during this period. These latter studies are particularly important for understanding the relationships between long-term changes in global climates, patterns of past geographic distributions, and resulting patterns of mammalian speciation.
