Kebara 2: new insights regarding the most complete Neandertal thorax

In this study, we present a new analysis of the costal skeleton of the Kebara 2 Neandertal that challenges the original description of the fossil remains. In addition to correcting an erroneous rib rejoin, we document that Kebara 2 shows significant metric and morphological differences in comparison to a wide range of modern human comparative samples. Moreover, Kebara 2's thorax is large, but it is not an isometrically scaled version of a modern human thorax. We also present updated information regarding additional Neandertal rib remains that weakens the case for previous speculations regarding marked ecogeographical patterning in the Neandertal upper thorax. From these results, in combination with various other lines of evidence, we hypothesize that the large chest of Neandertals, while different from modern humans, is not autapomorphic but instead related to a "primitive body bauplan": wide bodies with high body mass. A large thorax in pre-modern Homo, indicating a large vital capacity, would be consistent with the idea of increased oxygen consumption derived from higher energetic demands of a larger body and higher activity levels when compared to modern industrial samples. The likely presence of larger chests in the large bodied individuals from the middle Pleistocene of Eurasia and Africa (and even from the African lower Pleistocene) calls into question cold climate adaptation as a primary force for this skeletal morphology in Neandertals.