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Morphometrics and functional morphology of the fossil second metatarsal from Sedia del Diavolo (MIS 7, Latium, Italy)

Sedia del Diavolo is an archaeological site located in the low valley of the Aniene river (Rome, Latium) that, despite being known since the end of the 19th century, has been thoroughly investigated since the 1930’s. The site yielded a lithic assemblage referrable to the Middle Palaeolithic as well as numerous fossil remains, including two human specimens: a fragment of a femoral diaphysis (SdD1) and a complete second metatarsal (SdD2). Initially the site was dated to the end of the Middle Pleistocene and, coherently with the intended chronology, the first anthropological analysis attributed the remains to Homo neanderthalensis. Recently, a reappraisal of the geochronology of the sites of the low valley of the Aniene river redated Sedia del Diavolo to MIS 7, between 295-290 ka, making the site one of the oldest occurrences of the Levallois technology ever found in Europe. This contribution presents new advanced morphological analyses of SdD2, which shows signs of a probable stress fracture on the distal portion of the diaphysis. We obtained high resolution images of SdD2 by means of laboratory-based X-ray computed micrortomography at the FAITH station of the Elettra synchrotron in Trieste (Italy). We used cross-sectional geometry to investigate the robustness of the diaphysis and geometric morphometric approach to analyse the shape of the epiphyses. Results were compared to a series of modern human and fossil hominin second metatarsals. SdD2 is characterized by thicker cortical bone than H. sapiens and H. neanderthalensis. This suggests that the individual likely experienced high levels of mechanical loading and mobility. Moreover, the distribution of the bone around the longitudinal axis as well as the morphology of the proximal epiphysis make it more similar to H. sapiens than to H. neanderthalensis. Although results may be influenced by the presence of the stress fracture, the analyses suggest that the metatarsal belonged to an individual whose morphology was less derived than the more recent Neandertal comparative specimens.

fossil hominin ; second metatarsal ; Middle Pleistocene

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