Morphology and function of the lumbar spine of the Kebara 2 Neandertal

Abstract

The morphology of the lumbar spine is crucial for upright posture and bipedal walking in hominids. The excellent preservation of the lumbar spine of Kebara 2 provides us a rare opportunity to observe a complete spine and explore its functionally relevant morphology. The lumbar spine of Kebara 2 is analyzed and compared with the lumbar spines of modern humans and late Pleistocene hominids. Although no size differences between the vertebral bodies and pedicles of Kebara 2 and modern humans are found, significant differences in the size and orientation of the transverse processes (L(1)-L(4)), and the laminae (L(5), S(1)) are demonstrated. The similarity in the size of the vertebral bodies and pedicles of Kebara 2 and modern humans suggests similarity in axial load transmission along the lumbar spine. The laterally projected (L(2)-L(4)) and the cranially oriented (L(1), L(3)) transverse processes of Kebara 2 show an advantage for lateral flexion of the lumbar spine compared with modern humans. The characteristic morphology of the lumbar spine of Kebara 2 might be related to the wide span of its pelvic bones.

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

“…2) from the El Sidrón sample, are characterized by strongly posteriorly oriented transverse processes. This is particularly evident in the geometric morphometric comparisons with the modern human reference sample and fits with images of T10 of Regourdou 1 (Gómez-Olivencia et al, 2013a) and T12 of Kebara 2 (Been et al, 2010), and images presented in Gómez-Olivencia (2013a, b) as well as images presented by Arensburg (1991).…”

“…Interestingly, Been et al (2010Been et al ( , 2017a) also find a more cranial orientation of the transverse processes of lumbar vertebrae in Neandertals similar to the cranial orientation of the transverse processes of the thoracic vertebrae (Fig. 7).…”

“…It seems therefore that a common axial muscular factor links the orientations of the spinous processes of lower cervical vertebrae and thoracic vertebrae with specific functional implications in the cervical areas, associated with head-neck relations, and in the thoracic areas, associated with postural stability. Similar to Jellema et al (1993) and Ward et al (2012), spinous process orientation was linked with biomechanical implications in lumbar vertebrae with respect to spine leverage (Been et al, 2010) because greater horizontal projection increases the moment arms of erector spinae muscles attaching to them. These authors suggest further that greater horizontal orientation implies less "imbrication" and thus greater mobility.…”

“…This geometric effect, together with the fact that Neandertal ribs are longer, particularly in the middle and lower thorax (Franciscus and Churchill, 2002;Gómez-Olivencia et al, 2009;García-Martínez et al, 2014a), allows us to establish the hypothesis that the greater thorax capacity in Neandertals is not only the result of rib elongation (Franciscus and Churchill, 2002;Gómez-Olivencia et al, 2009;García-Martínez et al, 2014a), but also of a greater dorsal orientation of the rib attachments at the transverse processes of thoracic vertebrae (Bastir et al, 2015b). Arensburg (1991) and Been et al (2010, their (Gómez-Olivencia, 2013a, b;Gómez-Olivencia et al, 2013a). These studies suggested further subtle and variable differences, such as greater laminae heights in the first and second thoracic vertebrae in La Ferrassie 1, shorter spinous processes in La Ferrassie 1 and Kebara 2 (Gómez-Olivencia, 2013a), and smaller median heights in some vertebral bodies (T7, T10, T11) of Regourdou 1 .…”

Middle Pleistocene lower back and pelvis from an aged human individual from the Sima de los Huesos site, Spain

“…The lumbar vertebrae. The overall size (maximum dorsoventral diameter) of the most complete lumbar vertebrae (L3-L5) of this specimen is similar to the mean (L4) or significantly larger (L3 and L5) than our modern male comparative samples, and close to or slightly larger than those Neandertal males preserving the lumbar region (7,22,23) (SI Appendix, Tables S4 and S6). The transverse processes in L3 and L5 are significantly longer than modern human males and similar (L5) or even longer (L3) than in Neandertals.…”