Late Hemphillian monodactyl horses (Mammalia, Equidae) from the Bone Valley Formation of central Florida

Abstract

Isolated cheek teeth of the hypsodont one-toed horses Astrohippus stocki and Dinohippus mexicanus are described from ten localities within the classic vertebrate-bearing beds of the Bone Valley phosphate mining district and one new locality (containing the Lockwood Meadows Local Fauna) in Sarasota, Florida. All occurrences of these taxa are from the upper Bone Valley Formation and further confirm a late Hemphillian (late Miocene to early Pliocene) age, or within the range of about 5.4 to 4.5 myBP for this part of the sedimentary sequence. In contrast to the common occurrences of hipparions in the Bone Valley Formation, A. stocki and D. mexicanus are relatively rare. In some dental charcters such as protocone length and crown height, A. stocki and D. mexicanus are no more advanced in their stage of evolution than the advanced three-toed horses Neohipparion eurystyle, N. gidleyi and Nannippus peninsulatus.