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Mandibular Corpus (mandibular + corpus)
Selected AbstractsSize variation in early human mandibles and molars from Klasies River, South Africa: Comparison with other middle and late Pleistocene assemblages and with modern humans,AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 2 2009Danielle F. Royer Abstract Previous studies of the Middle Stone Age human remains from Klasies River have concluded that they exhibited more sexual dimorphism than extant populations, but these claims have not been assessed statistically. We evaluate these claims by comparing size variation in the best-represented elements at the site, namely the mandibular corpora and M2s, to that in samples from three recent human populations using resampling methods. We also examine size variation in these same elements from seven additional middle and late Pleistocene sites: Skh,l, Dolní V,stonice, Sima de los Huesos, Arago, Krapina, Shanidar, and Vindija. Our results demonstrate that size variation in the Klasies assemblage was greater than in recent humans, consistent with arguments that the Klasies people were more dimorphic than living humans. Variation in the Skh,l, Dolní V,stonice, and Sima de los Huesos mandibular samples is also higher than in the recent human samples, indicating that the Klasies sample was not unusual among middle and late Pleistocene hominins. In contrast, the Neandertal samples (Krapina, Shanidar, and Vindija) do not evince relatively high mandibular and molar variation, which may indicate that the level of dimorphism in Neandertals was similar to that observed in extant humans. These results suggest that the reduced levels of dimorphism in Neandertals and living humans may have developed independently, though larger fossil samples are needed to test this hypothesis. Am J Phys Anthropol, 2009. © 2009 Wiley-Liss, Inc. [source] Masticatory stress and the mechanics of "wishboning" in colobine jawsAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 3 2009David J. Daegling Abstract Cercopithecoid monkeys experience relatively high strains along the lingual aspect of the mandibular symphysis because of lateral transverse bending of the mandibular corpora ("wishboning") during mastication. Hylander (Am J Phys Anthropol 64 (1984) 1,46; Am Zool 25 (1985) 315,330) demonstrated that the distribution of strains arising from wishboning loads is comprehensible with reference to the mechanics of curved beams. Theory of curved beams suggests that lingual tensile strains are some multiple of labial compressive strains, yet limitations of experimental methods and uncertainty in estimating parameters needed for theoretical calculations have confounded attempts to characterize the magnitude of this disparity of normal strains. We evaluate the theoretical disparity of normal strains in wishboning in comparison to in vitro strains collected under controlled loads for a sample of mandibles representing two colobine species (N = 6). These data suggest that in colobine monkeys, maximum normal lingual strains should be at least twice maximum labial strains. In addition, we reexamine the distribution of symphyseal stress under an assumption of asymmetric bending, a general approach for calculation of stress appropriate for members that lack a plane of symmetry and are bent along an axis that is not coincident with the member's principal axes. Under asymmetric bending in colobine mandibles, the effect of symphyseal inclination on lingual strain is mitigating at the superior transverse torus and exacerbating at the inferior transverse torus. Relative compliance of colobine mandibular bone further supports the hypothesis that the structural and material properties of the colobine mandibular symphysis do not represent a morphological strategy for minimizing masticatory strain. Am J Phys Anthropol, 2009. © 2008 Wiley-Liss, Inc. [source] Lingual cortical mandibular defects (Stafne's defect): an anthropological approach based on prehistoric skeletons from the Canary IslandsINTERNATIONAL JOURNAL OF OSTEOARCHAEOLOGY, Issue 2 2002John R. Lukacs Abstract While posterior lingual mandibular depressions (Stafne's defect) are often discussed in clinical reports, they are rarely the subject of anthropological research. This situation is paradoxical since osteologists and skeletal biologists are in a position to enhance understanding of the trait's aetiology by systematically recording the trait in recent and prehistoric skeletal collections. This report reviews anthropological studies of cortical defects of the mandible, recommends a protocol for recording observations in trait variation, and presents new data for the prevalence of Stafne's defect,lingual cortical defects of the mandibular corpus. Among the Guanches of Tenerife in the Canary Islands (Spain), the prevalence of lingual cortical defects is 3.32% (15/452), males are more frequently affected than females, and there is a tendency for individuals with antemortem tooth loss to display larger lesions than individuals without antemortem loss of teeth. Defects of the left side are somewhat more variable in position than defects located on the right. In comparative perspective, prevalence of lingual cortical defects among the Guanches is high, given the overall 1.07% prevalence reported for archaeological series (Finnegan & Marcsik,1980), but is similar to figures reported for the Avar period sample from Hungary 3.73%. Prospects for the use of lingual cortical defects as non-metric traits of value in population distance studies remain uncertain since variation in trait expression may have a high environmental component. However, if human osteologists routinely include observations of lingual mandibular cortical defects in their analysis of skeletal collections, the data required to elucidate factors responsible for the trait's cultural, ecological, temporal and geographical patterning will more rapidly become established. Copyright © 2002 John Wiley & Sons, Ltd. [source] Time series analysis of jaw muscle contraction and tissue deformation during mastication in miniature pigsJOURNAL OF ORAL REHABILITATION, Issue 1 2004Z. J. Liu summary, Masticatory muscle contraction causes both jaw movement and tissue deformation during function. Natural chewing data from 25 adult miniature pigs were studied by means of time series analysis. The data set included simultaneous recordings of electromyography (EMG) from bilateral masseter (MA), zygomaticomandibularis (ZM) and lateral pterygoid muscles, bone surface strains from the left squamosal bone (SQ), condylar neck (CD) and mandibular corpus (MD), and linear deformation of the capsule of the jaw joint measured bilaterally using differential variable reluctance transducers. Pairwise comparisons were examined by calculating the cross-correlation functions. Jaw-adductor muscle activity of MA and ZM was found to be highly cross-correlated with CD and SQ strains and weakly with MD strain. No muscle's activity was strongly linked to capsular deformation of the jaw joint, nor were bone strains and capsular deformation tightly linked. Homologous muscle pairs showed the greatest synchronization of signals, but the signals themselves were not significantly more correlated than those of non-homologous muscle pairs. These results suggested that bone strains and capsular deformation are driven by different mechanical regimes. Muscle contraction and ensuing reaction forces are probably responsible for bone strains, whereas capsular deformation is more likely a product of movement. [source] Quantifying Mental Foramen Position in Extant Hominoids and Australopithecus: Implications for its Use in Studies of Human EvolutionTHE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 8 2010Chris A. Robinson Abstract The location of the mental foramen on the mandibular corpus has figured prominently in debates concerning the taxonomy of fossil hominins and Gorilla gorilla. In this study we quantify the antero/posterior (A/P) position of the mental foramen across great apes, modern humans and Australopithecus. Contrary to most qualitative assessments, we find significant differences between some extant hominoid species in mental foramen A/P position supporting its potential usefulness as a character for taxonomic and phylogenetic analyses of fossil hominoids. Gorilla gorilla, particularly the eastern subspecies, with a comparatively longer dental arcade and fossil and extant hominins with reduced canines and incisors tend to exhibit more anteriorly positioned mental foramina. Conversely, Pan troglodytes exhibits more posteriorly positioned mental foramina. Variation in this character among Gorilla gorilla subspecies supports recent taxonomic assessments that separate eastern and western populations. In all taxa other than Pan troglodytes the A/P position of the mental foramen is positively allometric with respect to dental arcade length. Thus, within each of these species, specimens with longer dental arcades tend to have more posteriorly positioned mental foramina. Those species with greater sexual dimorphism in canine size and dental arcade length (i.e., Gorilla gorilla and Pongo pygmaeus) exhibit more extreme differences between smaller and larger individuals. Moreover, among great apes those individuals with greater anterior convergence of the dental arcade tend to exhibit more posteriorly positioned mental foramina. Dental arcade length, canine crown area and anterior convergence are all significantly associated with mental foramen A/P position, suggesting that these traits may influence taxonomic variation in the A/P position of the mental foramen. Anat Rec 293:1337,1349, 2010. © 2010 Wiley-Liss, Inc. [source] | ||||||||||