Late Miocene Nannippus (Mammalia: Perissodactyla) from Florida, with a description of the smallest hipparionine horse

ABSTRACT

Late Clarendonian and very early Hemphillian horse teeth from Florida previously identified as early members of Nannippus aztecus (=N. minor) are referred instead to N. westoni (Simpson). N. westoni was originally assigned to Merychippus and thought to date from the early Miocene. The very low crown height in the teeth of the type specimen is the result of heavy attritional wear and is not of phylogenetic significance. N. westoni displays a mixture of derived Nannippus and primitive hipparionine character states, both in its cheekteeth and metapodials. N. morgani, sp.nov. is described from a small sample of diminutive, isolated teeth and a medial metatarsal that occur in late early Hemphillian faunas together with N. aztecus. N. morgani is 15 to 20% smaller in dental parameters than mean values for N. aztecus, making it one of the smallest known hipparionines, with an estimated body mass of about 40 kg. Three similar-sized, diminutive equids, N. morgani, Pseudhipparion skinneri, and Calippus elachistus, lived contemporaneously in the very late Miocene of Florida.