1Paleoanthropology group - Department of Paleobiology, Museo Nacional de Ciencias Naturales (CSIC), Madrid (Spain), 2Falculty of Medicine - Department of Stomatology, University Rey Juan Carlos, Madrid-Alcorcon (Spain), 3Department of Theoretical Biology, University of Vienna, Vienna (Austria)
Friday All day, Clinch Concourse
In chimpanzees and modern humans, symphyseal growth includes a forward shift of the mental region leading to a vertical symphysis in chimpanzee fetuses, but a mental prominence in human infants. It is suggested that this displacement may be associated with spatial changes in the back of the vocal tract delimited by the cranial base, the upper mid-face, the cervical column and the hyoid bone. Our study aims to examine this hypothesis.
The sample consists of 3D reconstructed jaw-basicranium-cervical skeletons based on CT-scans of 8 chimpanzee fetuses and 36 human infants, from birth to 5.5 years. On each specimen, we digitized 668 semi-landmarks and converted these to shape-variables by Procrustes superimposition to compare chimpanzee and human ontogenetic shape changes.
Our results show that in chimpanzeesand humans, the forward positioning of the mental region is associated with the space restriction at the back of the vocal tract due to upper mid-face retraction, resulting from cranial base flexion. In humans the space restriction is associated with the development of the upright body posture and the descent of the hyoid bone, whereas in chimpanzees it is associated with flexion of the head towards the throat, related to the fetal position, and the ascent of the hyoid bone.
These findings suggest that the development of a vertical symphysis in chimpanzees and a prominent mental region in humans may provide space for the tongue and the suprahyoid muscles in order to preserve the functionality of the laryngopharynx.
Fondation Fyssen Paris; CGL2009-09013, CGL2012-37279 (Spanish Ministry for Science and Competition)