title: Covariation in the human masticatory apparatus.
abstract: Many studies have described shape variation of the modern human cranium in relation to subsistence; however, patterns of covariation within the masticatory apparatus (MA) remain largely unexplored. The patterns and intensity of shape covariation, and how this is related to diet, are essential for understanding the evolution of functional masticatory adaptations of the human cranium. Within a worldwide sample (n = 255) of 15 populations with different modes of subsistence, we use partial least squares analysis to study the relationships between three components of the MA: upper dental arch, masseter muscle, and temporalis muscle attachments. We show that the shape of the masseter muscle and the shape of the temporalis muscle clearly covary with one another, but that the shape of the dental arch seems to be rather independent of the masticatory muscles. On the contrary, when relative positioning, orientation, and size of the masticatory components is included in the analysis, the dental arch shows the highest covariation with the other cranial parts, indicating that these additional factors are more important than just shape with regard to covariation within the MA. Covariation patterns among these cranial regions differ mainly between hunting-fishing and gathering-agriculture groups, possibly relating to greater masticatory strains resulting from a large meat component in the diet. High-strain groups show stronger covariation between upper dental arch and masticatory muscle shape when compared with low-strain groups. These results help to provide a clearer understanding of constraints and interlinkage of shape variation within the human MA and allow for more realistic modeling and predictions in future biomechanical studies.
authors.affiliation: Paleoanthropology Section, Senckenberg Center for Human Evolution and Paleoenvironment, Eberhard Karls Universität Tübingen, Tübingen, Germany.
authors.forename: Marlijn L
authors.initials: ML
authors.lastname: Noback
authors.forename: Katerina
authors.initials: K
authors.lastname: Harvati
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena / Q000502:physiology; D003724:Dental Arch / Q000033:anatomy & histology / Q000502:physiology; D005260:Female; D005502:Food; D006801:Humans; D008297:Male; D008410:Masticatory Muscles / Q000033:anatomy & histology / Q000502:physiology; D008433:Mathematics; D008954:Models, Biological; D012886:Skull / Q000033:anatomy & histology / Q000502:physiology; D013284:Stomatognathic System / Q000033:anatomy & histology* / Q000502:physiology*; D013704:Temporomandibular Joint / Q000033:anatomy & histology / Q000502:physiology
keywords: PLS analysis; dental arch; diet; masseter muscle; subsistence; temporalis muscle