The role of allometry and posture in the evolution of the hominin subaxial cervical spine.
Cervical vertebrae not only protect the spinal cord but also are the insertion and origin points for muscles related to the movement of the head, upper limb, and trunk, among others, and are thus important elements in primate evolution. While previous work has been undertaken on the first two cervical vertebrae, there is a dearth of studies on the subaxial cervical spine in hominines. In this paper, we provide detailed morphological information on two important aspects of the subaxial cervical vertebrae (C3 - C7): mid-sagittal morphology and superior facet orientation. We studied large samples of African apes including modern humans and the most complete fossil hominin subaxial cervical vertebrae using both traditional and geometric morphometrics. There are significant differences between extant hominoids related to the relative length and orientation of the spinous process as well as to the orientation of the articular facets, which are related to size, locomotion, and neck posture. In fact, fossil hominins do not completely conform to any of the extant groups. Our assessment of mid-sagittal morphology and superior articular facet orientation shows that australopiths have more Homo-like upper subaxial cervical vertebrae coupled with more "primitive" lower cervical vertebrae. Based on these results, we hypothesize that those changes, maybe related to postural changes derived from bipedalism, did not affect the entire subaxial cervical spine at once. From a methodological point of view, the combination of traditional and geometric morphometric data provides a more integrative perspective of morphological change and evolution, which is certainly useful in human evolutionary studies.
Dept. Estratigrafía y Paleontología, Facultad de Ciencia y Tecnología, Euskal Herriko Unibertsitatea, UPV-EHU. Apdo. 644, 48080 Bilbao, Spain. Electronic address: mikel.arlegui@ehu.eus.
Mikel
M
Arlegi
Dept. Estratigrafía y Paleontología, Facultad de Ciencia y Tecnología, Euskal Herriko Unibertsitatea, UPV-EHU. Apdo. 644, 48080 Bilbao, Spain; IKERBASQUE, Basque Foundation for Science, Spain; Équipe de Paléontologie Humaine, UMR 7194, CNRS, Département de Préhistoire, Muséum national d'Histoire naturelle, Musée de l'Homme, 17, Place du Trocadéro, 75016 Paris, France; Centro UCM-ISCIII de Investigación sobre Evolución y Comportamiento Humanos, Avda. Monforte de Lemos 5 (Pabellón 14), 28029 Madrid, Spain. Electronic address: asier.gomezo@ehu.eus.
Asier
A
Gómez-Olivencia
Équipe de Paléontologie Humaine, UMR 7194, CNRS, Département de Préhistoire, Muséum national d'Histoire naturelle, Musée de l'Homme, 17, Place du Trocadéro, 75016 Paris, France.
Lou
L
Albessard
Área de Antropología Física, Depto. de Ciencias de la Vida, Universidad de Alcalá, Alcalá de Henares 28871, Spain; Centro UCM-ISCIII de Investigación sobre Evolución y Comportamiento Humanos, Avda. Monforte de Lemos 5 (Pabellón 14), 28029 Madrid, Spain.
Ignacio
I
Martínez
Équipe de Paléontologie Humaine, UMR 7194, CNRS, Département de Préhistoire, Muséum national d'Histoire naturelle, Musée de l'Homme, 17, Place du Trocadéro, 75016 Paris, France; Department of African Zoology, Royal Museum for Central Africa, Tervuren, Belgium.
Antoine
A
Balzeau
Dpto. de Paleontología, Fac. Ciencias Geológicas, Universidad Complutense de Madrid, Avda. Complutense s/n, Madrid 28040, Spain; Équipe de Paléontologie Humaine, UMR 7194, CNRS, Département de Préhistoire, Muséum national d'Histoire naturelle, Musée de l'Homme, 17, Place du Trocadéro, 75016 Paris, France.
Juan Luis
JL
Arsuaga
Physical Therapy Department, Faculty of Health Professions, Ono Academic College, Kiryat Ono 5545173, Israel; Department of Anatomy and Anthropology, Sackler Faculty of Medicine, Tel Aviv University, 39040 Tel Aviv, Israel.
Ella
E
Been
D000818:Animals; D005075:Biological Evolution; D002574:Cervical Vertebrae / Q000033:anatomy & histology*; D005260:Female; D005580:Fossils / Q000033:anatomy & histology; D015186:Hominidae / Q000033:anatomy & histology* / Q000502:physiology*; D008124:Locomotion; D008297:Male; D011187:Posture
Fossil hominins; Geometric morphometrics; Locomotion; Postcranium; Traditional morphometrics