The relevance of the first ribs of the El Sidrón site (Asturias, Spain) for the understanding of the Neandertal thorax

Abstract

The paleobiological significance of the rib cage in Neanderthal ranges from functional anatomy, energetics to the general evolution of human body shape. However, despite this importance there is still debate as to the nature and extent of variations in size and shape of the Neanderthal thorax.The El Sidrón Neanderthals can contribute to this debate providing new thoracic remains (N=245) ranging from fully preserved and undistorted ribs to highly fragmented elements.

Three-dimensional morphometrics of thoracic vertebrae in Neandertals and the fossil evidence from El Sidrón (Asturias, Northern Spain)

“…1, 2, 6c) might indicate subtle biomechanical differences in breathing kinematics in Neandertals. Sagittal-cranial orientation of these facets facilitate vertical and oblique gliding movements, allowing for greater medio-lateral expansions , particularly in combination with longer ribs possibly in response to greater diaphragmatic action on central and lower parts of the thorax (T7-T10; Franciscus and Churchill, 2002;Gómez-Olivencia et al, 2009;García-Martínez et al, 2014a;Bastir et al, 2015a). All these aspects are compatible with bio-energetic arguments related to greater muscle and body mass estimates in Neandertals.…”

“…With respect to the El Sidrón fossils, the analysis of centroid size (Fig. 4) supports an assignment of SD-1619 to a young (and not so large) adult and of SD-1641 to In a more general morphological framework, the current study addressed the hypothesis that the enlarged thorax of Neandertals is not only the result of larger ribs (Franciscus and Churchill, 2002;Gómez-Olivencia et al, 2009;García-Martínez et al, 2014a, Bastir et al, 2015a, but also of a more dorsal orientation of the transverse processes of the thoracic vertebrae (Bastir et al, 2015b). A similar kind of influence of vertebral shape on rib cage morphology has been proposed in Australopithecus (Ward et al, 2012) and Homo ergaster/erectus (Jellema et al, 1993;Latimer and Ward, 1993), and more recently also identified as a geometric feature of modern human sexual dimorphism García-Martínez et al, 2016a).…”

“…Also, Neandertal rib shape differs from that of modern humans in a way that contributes to larger thorax capacity. Several researchers have observed an elongated midshaft of the ribs and also reduced torsion, suggesting a deep and wide chest in Neandertals (Franciscus and Churchill, 2002;Gómez-Olivencia et al, 2009;Bastir et al, 2012;Bastir et al, 2015a;García-Martínez et al, in revision).…”

“…Recent research on fossil ribs has provided solid evidence for capacious dimensions of the Neandertal thorax (Franciscus and Churchill, 2002;Gómez-Olivencia et al, 2009;García-Martínez et al, 2014a, in revision;Bastir et al, 2015a). A recent threedimensional (3D) assessment of rib size in Kebara 2 has shown that the ribs close to the diaphragm (ribs at levels 6-9) are larger than in modern humans, which is valid both absolutely as well as relative to body size (e.g., estimates of stature, García-Martínez et al, 2014a).…”

“…This is because the rib cage is an anatomical complex, composed by ribs that are dorsally connected with the thoracic vertebrae at the costo -vertebral and -transverse joints, and ventrally with the sternum by the costosternal cartilages. Consequently, the size and shape of the thorax as well as its capacity depend on the size and shape of the ribs (Franciscus and Churchill, 2002;Gómez-Olivencia et al, 2009;García-Martínez et al, 2014a;Bastir et al, 2015a), the sternum (Gómez-Olivencia et al 2012), and on the morphology of the thoracic vertebrae (Bastir et al, 2015b).…”