Extant African papioninans are distinguished from macaques by the presence of excavated facial fossae; however, facial excavation differs among taxa. Mangabeys (Cercocebus, Rungwecebus, and Lophocebus) exhibit fossae that invade the zygomatic forming pronounced suborbital fossae (SOFs). Larger-bodied Papio, Mandrillus, and Theropithecus have lateral rostral fossae with minimal/absent suborbital fossae. Because prior studies have shown that mangabeys exhibit adaptations to anterior dental loading (e.g., palatal retraction), it is plausible that mangabey SOFs represent structural accommodation to masticatory-system shape rather than facial allometry, as commonly hypothesized. We analyzed covariation between zygomaxillary-surface shape, masticatory-system shape, and facial size in 141 adult crania of Macaca fascicularis, Papio kindae, Cercocebus, and Lophocebus. These taxa represent the range of papionin SOF expression while minimizing size variation (narrow allometry). Masticatory-system landmarks (39) registered palate shape, bite points, masticatory muscle attachments, and the tempo-romandibular joint. Semilandmarks (450) captured zygomaxillary-surface shape. Following Procrustes superimposition with semilandmark sliding and principal components analyses, multivariate regression was used to explore allometry, and two-block partial least-squares analyses (within-configuration and separate-blocks) were used to examine covariation patterns. Scores on principal components 1e2 and the first partial least-square (PLS1) separate mangabeys from Macaca and Papio. Both zygomaxillary-surface shape and masticatory-system shape are correlated with size within taxa and facial morpho-types; however, regression distributions indicate morphotype shape differences are non-allometric. PLS1 accounts for-95% of shape covariance (p < 0.0001) and shows strong linear correlations (r-PLS 1/4-0.95, p < 0.0001) between blocks. Negative PLS1 scores in mangabeys reflect deep excavation of the suborbital malar surface, palatal retraction, and anterior displacement of jaw adductor muscles and the temporo-mandibular joint. Neither PC1 nor PLS1 scores ordinate specimens by facial size. Taken together, these results fail to support the allometric hypothesis but suggest that mangabey zygomaxillary morphology is closely linked with adaptations to hard-object feeding.(C) 2021 Elsevier Ltd. All rights reserved.

Many authors have hypothesized an association between rates of morphological evolution and rates of species diversification, however, this association has yet to be empirically tested in the primate cranium. In this investigation, we used phylogeny-based approaches to examine the relationship between rates of species diversification, rates of cranial size and shape evolution, and observed cranial morphological disparity of extant catarrhines (Order: Primates). We used 34 3D landmarks digitized from 2038 crania representing 42 catarrhine species and a time-calibrated molecular phylogeny to determine the rates of evolution of cranial size and shape, rates of lineage diversification, and levels of morphological disparity by clade. The only significant relationship among these variables was for evolutionary rates of size and shape change. We discuss these results in the context of primate and mammalian macroevolution, and in light of the proposed hypothesis that size is a “line of least evolutionary resistance” in cranial evolution.

While the analysis of ontogenetic trajectories is common in geometric morphometrics (GM), the simultaneous comparison of several trajectories can be unwieldy and is, in some cases, unable to make use of one of the main advantages of GM, visualization. Furthermore, due to the paucity of the paleontological record, analyses of trajectories are often limited to extant taxa. We address these issues by presenting a method for visualizing the similarities and differences of cranial ontogenetic trajectories among taxa and a method for reconstructing ancestral ontogenetic trajectories, so that these differences can be investigated in a phylogenetic context. We also tested for the presence of phylogenetic signal in the ontogenetic trajectories themselves. Using an ontogenetic series of 522 crania, representing 17 cercopithecine species from 8 genera, we first calculated ontogenetic trajectories of cranial shape change for each species, and then entered these trajectories into a principal components analysis to produce a developmental shape-change trajectory PCA (δPCA). Then, through an augmentation of the phylomorphospace approach, we projected a molecular phylogeny onto the major axes of trajectory shape variation from the δPCA to produce an 'ontophylomorphospace,' using squared-change parsimony to reconstruct interior nodes. Through these procedures, we were able to determine that the δPCAs illustrate patterns of variation in these developmental trajectories in a visually intuitive manner that allows for easier comparisons among taxa. Through examination of the ontophylomorphospace, we found that African papionins exhibit extensive homoplasy in the evolution of cranial ontogenetic trajectories, and that Asian species of Macaca show highly derived ontogenetic trajectories relative to other cercopithecines. Additionally, we found no support for the presence of a phylogenetic signal in cranial ontogenetic trajectories. The δPCA and the ontophylomorphospace are ways in which to visualize and compare complex, multivariate shape transformations, both among extant taxa and over evolutionary time, respectively.

OBJECTIVESThe smallest extant member of genus Papio, the Kinda baboon exhibits low sexual dimorphism and a distinctive cranial shape. Ontogenetic scaling accounts for most cranial-shape differences within Papio, but studies have shown that the Kinda follows a separate ontogenetic trajectory. If so, its cranial-dimorphism pattern should differ from other subspecies. To evaluate this hypothesis, morphometric analysis was used to investigate cranial dimorphism in Papio.MATERIALS AND METHODSThree-dimensional landmarks were digitized on 434 adult crania representing six Papio subspecies. Size- and shape-dimorphism magnitudes were quantified using centroid size and Procrustes distances. Patterns of sex- and size-related variation were explored using MAN(C)OVA, multivariate regression, and form-space PCA. Canine dimorphism was investigated using dental metrics.RESULTSKinda size and shape dimorphism are significantly lower than in other Papio subspecies. The relative magnitude of Kinda shape dimorphism is similar to other southern baboons; Kinda canine dimorphism is unremarkable. MAN(C)OVA results support subspecies differences in cranial dimorphism and scaling. Allometric and dimorphism vectors differ significantly in some subspecies, and their vector-angle matrices are strongly correlated. The Kinda's allometric vector angles are divergent. Form-space PC3, summarizing size-independent dimorphism, separates the Kinda from other subspecies.DISCUSSIONThe Kinda baboon exhibits significantly lower size and shape dimorphism than other baboons, but its relative dimorphism levels are unexceptional. The Kinda differs from other subspecies in patterns of allometry, size-related shape dimorphism, and residual shape dimorphism. Kinda facial shape is "masculinized" relative to size, especially in females, suggesting female sexual selection contributed to the evolution of Kinda dimorphism.

Disarticulation of the human hip is among the most arduous joint dissections routinely performed in gross anatomy laboratories. The force required to distract the femoral head can fracture the femur or acetabulum, especially when applied by inexperienced student dissectors to a geriatric donor. We conducted a literature review to better understand the factors that contribute to passive stabilization of the hip in hopes of minimizing use of force and averting hard and soft tissue damage during hip dissection. We found that early experiments by Weber and Weber (1837) first demonstrated the role of atmospheric pressure differentials in resisting distraction of the femoral head. Subsequent experimental research has clarified the relationship among three factors that contribute to this phenomenon: 1) the cross‐sectional area of the femoral head; 2) the saturated vapor pressure of synovial fluid at body temperature; and 3) the integrity of the acetabular labrum and the zona orbicularis of the joint capsule, the latter being necessary to maintain intra‐articular pressure levels. The force F required to distract the hip is given by F = (πD 2 /4) * (P a − P i ) , where D is the diameter of the femoral head (m), P a is atmospheric pressure (mBar), and P i is the saturated vapor pressure of synovial fluid at body temperature (mBar). Thus, equilibration of atmospheric and intra‐articular pressures should minimize or eliminate the force required for hip distraction. As a practical application to anatomical education, we have performed multiple standard hip dissections ( Grant's Dissector, 16 th ed.) with the additional step—following the example of Weber and Weber (1837)—of drilling a 3 mm hole in the acetabulum ~2 cm superior to the acetabular notch. Using this procedure, the femoral head slides easily from the socket with no need for the complex maneuvers described in many dissection manuals. Adoption of this technique should provide human anatomy students with a less stressful dissection experience, as well as the opportunity to directly observe the interplay of factors contributing to normal human hip function. Support or Funding Information This research was supported by the Midwestern University Department of Anatomy, and did not require IRB approval.

This study investigates the taxonomic and morphometric affinities of a newly catalogued fossil papionin from Kromdraai A. The juvenile specimen (KA 5993), which preserves the face and cranial base anterior to the spheno-occipital synchondrosis, is notable for its small size and well-developed maxillary fossae. Geometric morphometric analyses were conducted to test the hypothesis that KA 5993 represents a juvenile of Papio (hamadryas) angusticeps, the only small- to medium-sized papionin definitively recognized at Kromdraai. Three-dimensional landmarks and semilandmarks were collected from a digital 3D model of the KA 5993 specimen. The comparative sample comprised 232 juvenile and adult crania representing five extant papionin genera and two specimens of Papio (h.) angusticeps. To broaden comparisons, developmental simulation was used to estimate the subadult and adult morphologies of KA 5993.Sliding surface semilandmarkswere used to compare the zygomaxillary morphology of KA 5993 with juveniles of Lophocebus and Papio. The affinities of the KA 5993 specimen were assessed using Procrustes distances and principal components analysis. Additionally, its dental measurements were compared to those of extant and fossil papionins. Results show that KA 5993 represents a small member of the genus Papio. Its juvenile and estimated adult facial proportions are most similar to those of the extant Kinda baboon (Papio hamadryas kindae). It is distinguished from extant Papio by the presence of deeply excavated suborbital fossae with anteriorly projecting margins and from P. (h.) angusticeps by the narrower breadth and deeper excavation of its suborbital fossa; its greater relative facial breadth; and some qualitative and metric traits of the permanent dentition. These findings provide only limited support for the hypothesis that KA 5993 represents a juvenile of P. (h.) angusticeps. Rather, it may represent a previously unknown subspecies of P. hamadryas, possibly ancestral to the central African Papio clade that includes the modern Kinda baboon. Future studies including additional juvenile and adult specimens of P. (h.) angusticeps are necessary to clarify the taxonomic status of this specimen. In the interim, we provisionally refer this juvenile specimen to Papio hamadryas ssp. indet.

The three-dimensional configuration of the primate masticatory system is constrained by the need to maximize bite forces while avoiding distraction of the temporomandibular joint (TMJ). Within these bounds, shape variation has predictable effects on functional capacities such as mechanical advantage and gape. In this study, geometric morphometric analysis is used to investigate the ontogeny of masticatory function in papionin monkeys and test the hypothesis that biomechanical constraints determine the location of molar eruption. This "constrained eruption hypothesis" predicts that the distalmost molar (DMX) will occupy a consistent location anterior to the TMJ and that jaw adductor muscles will maintain consistent positions relative to both DMX and TMJ. Craniometric landmarks were digitized on cross-sectional ontogenetic series of nine papionin species. Form-space PCA of Procrustes residuals, visualization of Bookstein shape coordinates, and nonparametric ANOVA were used to identify ontogenetic shape trends and test for significant ontogenetic changes in relative landmark positions. In most taxa, DMX maintains a consistent position relative to the TMJ while the anterior dentition migrates anteriorly. Where significant intraspecific ontogenetic differences occur, they involve anterior migration of DMX in later dental stages, likely due to late adolescent growth of the posterior palate. Attachments of the anterior temporalis and deep masseter also maintain consistent positions relative to the TMJ; however, the superficial masseter migrates anteriorly throughout ontogeny. All muscle attachments migrate laterally relative to the TMJ, reflecting positive scaling of adductor PCSA. Overall, results support the constrained eruption hypothesis and suggest mechanisms by which functional capacity is maintained during ontogeny.