Allometry and advancing age significantly structure craniofacial variation in adult female baboons.

Primate craniofacial growth is traditionally assumed to cease upon maturation or at least be negligible, whereas bony remodeling is typically associated with advanced adult age and, in particular, tooth loss. Therefore, size and shape of the craniofacial skeleton of young and middle-aged adults should be stable. However, research on both modern and historic human samples suggests that portions of the CFS exhibit age-related changes in mature individuals, both related to and independent of tooth loss. These results demonstrate that the age-category 'adult' is heterogeneous, containing individuals demonstrating post-maturational age-related variation, but the topic remains understudied outside of humans and in the cranial vault and base. Our research quantifies variation in a sample of captive adult female baboons (n = 97) in an effort to understand how advancing age alters the mature CFS. Craniometric landmarks and sliding semilandmarks were collected from computed tomography (CT) scans of adult baboons aged 7-32 years old. To determine whether craniofacial morphology is sensitive to aging mechanisms and whether any such effects are differentially distributed throughout the cranium, geometric morphometric techniques were employed to compare the shapes of various cranial regions among individuals of increasing age. Unexpectedly, the biggest form differences were observed between young and middle-aged adults, rather than between adults with full dentitions and those with some degree of tooth loss. Shape variation was greatest in masticatory and nuchal musculature attachment areas. Our results indicate that the craniofacial skeleton changes form during adulthood in baboons, raising interesting questions about the molecular and biological mechanisms governing these changes.

Additive genetic variation in the craniofacial skeleton of baboons (genus Papio) and its relationship to body and cranial size.

OBJECTIVES: Determining the genetic architecture of quantitative traits and genetic correlations among them is important for understanding morphological evolution patterns. We address two questions regarding papionin evolution: (1) what effect do body and cranial size, age, and sex have on phenotypic (VP ) and additive genetic (VA ) variation in baboon crania, and (2) how might additive genetic correlations between craniofacial traits and body mass affect morphological evolution? MATERIALS AND METHODS: We use a large captive pedigreed baboon sample to estimate quantitative genetic parameters for craniofacial dimensions (EIDs). Our models include nested combinations of the covariates listed above. We also simulate the correlated response of a given EID due to selection on body mass alone. RESULTS: Covariates account for 1.2-91% of craniofacial VP . EID VA decreases across models as more covariates are included. The median genetic correlation estimate between each EID and body mass is 0.33. Analysis of the multivariate response to selection reveals that observed patterns of craniofacial variation in extant baboons cannot be attributed solely to correlated response to selection on body mass, particularly in males. DISCUSSION: Because a relatively large proportion of EID VA is shared with body mass variation, different methods of correcting for allometry by statistically controlling for size can alter residual VP patterns. This may conflate direct selection effects on craniofacial variation with those resulting from a correlated response to body mass selection. This shared genetic variation may partially explain how selection for increased body mass in two different papionin lineages produced remarkably similar craniofacial phenotypes.

Brief Communication: Skeletal and dental development in a sub-adult western lowland gorilla (Gorilla gorilla gorilla).

OBJECTIVES: Non-human primate growth trajectories are often used to estimate the age and life history traits of fossil taxa. The exclusive use of chimpanzee growth patterns to estimate developmental stages for the earliest hominins is problematic because incomplete lineage sorting in the hominoid clade has produced a mosaic human genome that contains different regions shared with any one of the great apes. The accidental death of a sub-adult male western lowland gorilla (Gorilla gorilla gorilla) provides not only an opportunity to compare the degree of dentoskeletal maturation in this individual with published data from conspecifics, but also insight into gorilla growth and development as it applies to modeling that of early hominins. MATERIALS AND METHODS: Dental stage was assessed for a sub-adult male western lowland gorilla by comparing dental eruption and calcification to established relative age categories. Ectocranial suture fusion, epiphyseal union, and long bone dimensions were compared to growth standards for wild male gorillas of a similar dental stage to determine developmental timing variability. RESULTS: Results suggest that greater variability exists in developmental rates and patterns and in morphological parameters than is often acknowledged. DISCUSSION: These results have implications for selecting appropriate models for studying extinct taxa. Ecological and physical characteristics shared between humans and gorillas may make gorilla life history equally valid in a comparative framework and encourage non-exclusive use of chimpanzee life history for paleoanthropological models.

Risk factors associated with deformational plagiocephaly.

OBJECTIVE: This study was designed to statistically evaluate the independent and interacting effects of biological and environmental risk factors that influence lateralization of deformational plagiocephaly (DP) in an attempt to provide future guidance for clinical treatment. METHODS: A database of >20000 children treated for DP was examined by using 2- and 3-way factor analyses for categorical frequency data, representing the largest statistical analysis of DP to date. Data on parity, zygosity, intrauterine presentation, birth number and weight, sleep position, lateralization, and sex were collected from parents of children with DP who were treated at Cranial Technologies, Inc, from 1990 to 2007. RESULTS: As with most DP studies, male patients were significantly overrepresented. Nonetheless, after statistically accounting for sex in our analyses, DP is significantly correlated with primiparity, fewer vertex but more breech and transverse intrauterine presentations, twinning (specifically, dizygosity), and, finally, right-sided lateralization. Additional analyses revealed that several factors correlated with DP, such as intrauterine presentation, sleep position, and lateralization, are not easily explained by an underlying biological factor. Instead, sleep position was the single greatest predictor of lateralization. CONCLUSION: Although previous studies have argued for both environmental and underlying biological factors associated with DP, we found that lateralization in children with DP could be largely explained by environmental factors such as sleep position.