FOSSIL HORSES, CARBON ISOTOPES AND GLOBAL CHANGE

Between 20 and 10 million years ago, Miocene horses demonstrate rapid dental evolution from low-crowned (brachydont) to high-crowned (hypsod ont) teeth. Hypsodonty is classically interpreted as an adaptive shift from browsing to grazing to exploit the spread of savanna grasses. Re cent geochemical studies allow the use of carbon isotopes to test this hypothesis. Isotopic analysis of fossil horse teeth indicates a predo minantly C-3 diet consisting of mixed browse/grass or predominantly C- 3 grasses until the latest Miocene. The advent of C-4 grassland ecosys tems began about 7-8 million years ago and seems related to declining equid diversity.