BUSCADOR RECOLECTA

Digital.CSIC. Repositorio Institucional del CSIC

oai:digital.csic.es:10261/287078

[Description of methods used for collection/generation of data] Landmarks and template generated by geometric morphometrics protocols in the software Viewbox 4.0. Codes of the software RStudio.-- The file "Sample.txt" is the description of the individuals whose landmarks appear in the file "Landmarks.txt". The file "Template.vbr" is the digitizing template used to collect these landmarks. The files "Integration-Modularity.txt" and "Motio-Morphology.txt" have the code used in the software RStudio to analyze the data., The first cervical vertebra, atlas, and its morphology has remained understudied until very recently despite being a central element of human anatomy, connecting the cranial and post-cranial skeletal systems. This condition makes it informative of both systems, their integration and the functionality that applies to them, such as the locomotor pattern, body posture or neck mobility, both in modern humans and extinct hominin species. However, basic factors of variability such as the possible sexual dimorphism of population variation are not known. As the atlas is badly preserved in the fossil record, it has been necessary to develop a quantitative reconstruction method in order to include in the sample several fragmented atlases. The technique used to carry out the reconstructions and the all the analyses in this thesis was high-density geometric morphometrics, analyzing a total of 119 landmarks and curve semilandmarks in more than a hundred atlas of hominins and chipanzees. Both the reconstructions and the high-density geometric morphometrics, used for the first time in the literature for the study of the atlas, have proved to be useful and, thanks to the data sharing, replicable. As a first approach to the atlas and the most relevant aspects of its morphology, we studied variability, integration and functionality of this bone in modern humans. We found that the atlas does not present sexual dimorphism but, as expected, there is a difference in size between sexes. Regarding the possible differences between populations, we found a significant variability, although contrary to what would be expected: the atlas of inuits and Africans does not share the pattern of torso shortening, presenting a greater vertebral height than Europeans. We could think that this is because atlas morphology is more related to the skull than to the rest of the spine, but thanks to the integration analysis we know that the atlas integration is greater with the axis (C2) than with the cranial base. Another important finding is that the atlas has a higher evolutionary integration than the static one. This means that the integration pattern shared with chimpanzees is stronger than the human pattern, which could decouple the atlas anatomy from the locomotor pattern, supporting some previous theories about the generality of this structure in order Primate species. The last analysis performed on modern humans tried to find a relationship between atlas morphology and the mobility of the atlanto-occipital and atlanto-axial joints. The result was positive and we observed that atlases with flatter superior articular facets and greater length show greater mobility, both in flexion-extension and rotation. Once the current variability of atlases, their integration and their morpho-functional relationship had been studied, we used this knowledge to study the atlases of extinct species. First, we analyzed atlases from the Krapina site (Croatia) in order to confirm the presence of a high number of anatomical variants in Neanderthals. These anatomical variants, found in other individuals of this species, are related to a low genetic diversity of populations. The analyses confirmed the high prevalence of anatomical variants in this site and an exhaustive bibliographic review suggests that the presence of anatomical variants in Pleistocene individuals would be much higher than in modern humans. We also studied the atlases from the El Sidrón site (Asturias), which allowed us to increase the well-preserved sample of adult Neanderthal atlases by 25%. The inclusion of these atlases in the Neanderthal sample increases its variability and reinforces the morphological differences between this species and ours, which point to a lower cervical lordosis in H. neanderthalensis. Furthermore, these differences point to the Neanderthal atlas being related to the particular skull anatomy of this species and to the fact that, probably, its morphology is derived, since it presents several anatomical particularities that are not present in any other species studied. Finally, we estimated the mobility of the atlas of several Neanderthals, finding that the range of motion of this species would be similar to that of modern humans, finding no significant differences. This contradicts previous hypotheses that considered the cervical spine of this species to be more stable and less mobile than that of H. sapiens. This thesis demonstrates that many of the previous hypotheses about the atlas of extinct species should be revised and studied in more depth. In fact, the first approaches to a more exhaustive analysis of the mobility of the upper cervical spine have already been made. The ontogeny of this structure and the study of the entire cervical spine are other aspects to be addressed in the future., Peer reviewed