The morphology of the foot in the Middle Pleistocene population of Sima de los Huesos

Abstract

The morphology of the human foot is closely related with locomotion and weight transmission. The preservation of Homo fossil foot remains previous to modern humans and Neandertals is very scarce throughout the fossil record. Previous studies have demonstrated that modern humans and Neandertal feet are similar in overall size and proportions and are indistinguishable in the implied locomotor capabilities. However, the robusticity and some metrical and morphological traits that characterize the Neandertal foot are different from that of modern humans. Due to the evolutionary and morphological relationship between Neandertals and the Sima de los Huesos (SH) sample, important information can be extracted from SH foot remains that is relevant to the understanding of the Neandertal foot evolution. Among more than 6500 human fossils recovered so far in SH, around 500 belong to the foot. They represent approximately the 60% of the foot remains of the Homo fossil record prior to Neandertals and Early Homo sapiens. This large collection offers an unprecedented opportunity to study the morphology of the foot in a population from the Middle Pleistocene, something that was not possible until the discovery and thorough excavation of the SH site. Here, we present a detailed metrical and morphological study of the foot remains from SH. The entire collection of foot remains from SH represents a minimum number of 16 individuals. As a whole, the morphology of the foot from SH is similar to that of Neandertals and modern humans except for the robusticity of the fossils. However, this study provides further features that allow to distinguish SH hominins from modern humans. Both the SH hominins and the Neandertals display tali with short necks and broad lateral malleolar facets, broad calcanei with long bodies and projected sustentaculum tali, stout naviculars, short intermediate cuneiforms and robust metatarsals and phalanges. In addition, the SH tali show small heads that are different from the large ones typical of the Neandertal tali. The morphological study of the foot bones from SH confirms the evolutionary relationship between this Middle Pleistocene population and the Neandertals. Nevertheless, some traits differentiate the SH hominins and Neandertal feet. These results are also in accordance with the proposed large corporal size for the SH population and its primitive biotype.