THE three-toed horse Hipparion was ubiquitous in terrestrial mammalian faunas throughout Holarctica during parts of the Miocene. This report describes Hipparion from the early Barstovian Fleming Formation of the Texas Gulf Coastal Plain. These specimens are assigned to Hipparion because of dental characters such as the diagnostic presence of isolated protocones in the upper molars. This Hipparion is also characterised by a well-developed and anteriorlyrimmed preorbital fossa similar to the condition seen in some Old World forms. Because of this earliest known occurrence, the widely used Hipparion datum concept should be restricted to some palaeogeographically finite area in the Old World.