Human calcanei from the Middle Pleistocene site of Sima de los Huesos (Sierra de Atapuerca, Burgos, Spain).

The existence of calcanei in the fossil record prior to modern humans and Neandertals is very scarce. This skeletal element is fundamental to understanding the evolution of the morphology of the foot in human evolution. Here we present and metrically and comparatively describe 29 calcaneus remains from the Middle Pleistocene site of Sima de los Huesos (SH) (Sierra de Atapuerca, Burgos, Spain). These calcanei belong to 15 individuals (nine adults, two adolescents and four immature individuals). The metric and morphological differences in the calcanei among Middle and Late Pleistocene hominins tend to be subtle. However, the calcanei from SH are broad and robust with large articular surfaces and most significantly, exhibit a very projected sustentaculum tali. A biomechanical and phylogenetic interpretation is proffered to explain the observed morphology of these calcanei. It has been possible to propose tentative sex assignments for the SH calcanei based on size, using methods similar to those used to establish sex from the talus bones from SH. The estimation of stature based on the calcaneus provides a mean of 175.3 cm for males and 160.6 for females, which is similar to that obtained using other skeletal parts from the site. In sum, the SH calcanei are robust with a proportionally long tubercle and a projected sustentaculum tali, which are traits shared by Neandertals.