Determining the gait of Miocene, Pliocene, and Pleistocene horses from fossilized trackways

Abstract. Much work has been done on the study of vertebrate gaits over the past several decades and efforts undertaken to apply this to fossil tracks, especially dinosaurs and mammals such as cats, dogs, camels, and horses. This work seeks to expand upon such studies and in particular to study footprints laid down in sand by modern horses and apply such studies to determine the gaits of fossil horse trackways. It thus builds upon the work of Renders (1984a, b) and Kienapfel et al. (2014) and suggests additional measurements that can be taken on horse footprints. In this study the footprints left in the sand by 15 horses of various breeds with various gaits were videotaped, photographed, described, and measured in order to determine characteristics useful in distinguishing gaits. These results were then applied to two new sets of fossil footprints, those of the middle Miocene merychippine horse Scaphohippus intermontanus that I personally examined and measured and those from the late Pleistocene horse Equus conversidens, previously illustrated and described in the literature (McNeil et al., 2007). The latter horse exhibits a fast gallop of around 9.4 m/s, but it is the former whose footprints are quite unique. The quantitative and visual features of these prints are suggestive of a medium-fast gait involving apparent “understepping” of diagonal couplets and hind feet that overlap the centerline. The gait that most closely matches the footprints of Scaphohippus is the “artificial” gait of a slow rack or tolt, or pace, around 1.9 m/s, though an atypical trot of a horse with major conformation issues or which is weaving (swaying) from side to side is a less likely possibility. This intimates, along with the earlier study of Renders (1984a, b), who found the artificial gait of the running walk displayed by Pliocene hipparionine horses, that ancient horses possessed a much greater variety of gaits than modern horses and that over time they lost these abilities with the exception of certain gaited breeds.