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

Abstract

Well-preserved thoracic vertebrae of Neandertals are rare. However, such fossils are important as their three-dimensional (3D) spatial configuration can contribute to the understanding of the size and shape of the thoracic spine and the entire thorax. This is because the vertebral body and transverse processes provide the articulation and attachment sites for the ribs. Dorsal orientation of the transverse processes relative to the vertebral body also rotates the attached ribs in a way that could affect thorax width.

Ribcage measurements indicate greater lung capacity in Neanderthals and Lower Pleistocene hominins compared to modern humans

“…Recent evidence suggests that the large TLC observed in Neanderthals compared to modern humans was the result of large ribs in the central–lower thorax coupled with a more dorsal orientation of the transverse processes in Neanderthals compared to modern humans, causing mediolateral expansion of the ribcage 18,20 . This ribcage morphology (Fig.…”

Eco‐geographic adaptations in the human ribcage throughout a 3D geometric morphometric approach

“…Even though this is just an extrapolation from Schmid's () hypothesis, it would be consistent with results on the bi‐iliac breadth of other authors (Holliday and Hilton, ), who found that Greenland Inuit are the ones that present larger values of this measurement, linked to a wide body shape which would include a large trunk. However, it has been recently observed that to fully account for the 3D thorax morphology, not only the ribs but also the thoracic vertebrae should be considered (Bastir et al, ; García‐Martínez, ; García‐Martínez et al, ). This is because the orientation of the transverse processes of the thoracic vertebrae could play an important role regarding the orientation of the ribs and the mediolateral amplitude of the thorax.…”

“…This is also due to the fact that 3D rib cage morphology can only be understood as the result of the sum of its metameric components: ribs and vertebrae (Bastir et al, ; García‐Martínez, ; García‐Martínez et al, ). Moreover, besides these technical limitations, researchers have paid more attention to the quantification of the thorax variability in fossil hominin species than in the study of modern human thoracic variability (Bastir et al, ; Chapman et al, ; Franciscus and Churchill, ; Gómez‐Olivencia, ; Gómez‐Olivencia et al, ; García‐Martínez et al, ; Latimer, Lovejoy, Spurlock, & Haile‐Selassie, ; Schmid, ; Schmid et al, ; Williams et al, ). Although one study included a cold‐adapted population, it was used as a comparative sample for addressing the possible cold‐adaptation in the Neanderthal Kebara 2 thorax (Gómez‐Olivencia et al, ).…”

“…Although the tubercle‐ventral arch, along with the tubercle‐ventral cord, is useful for quantifying differences in rib curvature in the cranial view (Gómez‐Olivencia et al, ), several attempts using angles have been used to try to quantify other important features, such as rib torsion (Jellema, Latimer, & Walker, ), but this feature is not well quantified using traditional measurements. This is because rib torsion modifies the curvature not only in the transverse plane but also in the saggital and the coronal planes (García‐Martínez et al, ), therefore necessitating for the use of 3D geometric morphometrics in order to quantify the 3D rib morphological variability (Bastir et al, ; Chapman et al, ; García‐Martínez et al, ; García‐Martínez, Torres‐Tamayo, Torres‐Sanchez, García‐Río, & Bastir, ; Shi et al, ; Weaver, Schoell, & Stitzel, ). Finally, Gómez‐Olivencia et al () did not account for latitude, which has been related to temperature.…”

“…For instance, it was hypothesized by Jellema et al () that the modern body shape and ribcage morphology (i.e., narrow in the caudal part and expanded in the cranial part) has remained invariable since its appearance with Homo ergaster . However, several studies dealing with the ribcage of other extinct hominin species, such as the Neanderthals, which are geologically younger than H. ergaster , found statistical differences in both size and shape between this species' ribcages and those of modern humans (Bastir et al, ; Franciscus and Churchill, ; García‐Martínez et al, ; Gómez‐Olivencia, ; Gómez‐Olivencia et al, ; Weinstein, ). This morphology, which was likely caused by an adaptation to high energetic requirements instead of by an adaptation to cold‐environments (Churchill, ; Froehle and Churchill, ), would support the evidence of recent variation in the rib cage morphology.…”