Orbit orientation in primates has been linked to adaptive factors related to activity pattern and size‐related variation in structural influences on orbit position. Although differences in circumorbital form between anthropoids and strepsirrhines appear to be related to interspecific disparities in levels of orbital convergence and orbital frontation, there is considerable overlap in convergence between suborders. Unfortunately, putative links between convergence and frontation across primates, and consequent arguments about primate and anthropoid origins, are likely to be influenced by allometry, the size range of a respective sample, and adaptive influences on encephalization and activity patterns. Such a multifarious system is less amenable to interspecific treatment across higher‐level clades. An ontogenetic perspective is one way to evaluate transformations from one character state to another, especially as they pertain to allometric effects on phenotypic variation. We characterized the ontogeny of orbital convergence and frontation in 13 anthropoid and strepsirrhine species. In each suborder, correlation and regression analyses were used to test hypotheses regarding the allometric bases of variation in orbital orientation. Growth trajectories were analyzed intra‐ and inter‐specifically. Frontation decreased postnatally in all taxa due to the negative scaling of brain vs. skull size. Further, interspecific variation in relative levels of frontation was linked to corresponding ontogenetic transpositions in encephalization that differed within both suborders. In strepsirrhines, postnatal increases in convergence were largely due to the negative allometry of orbit vs. skull size. In contrast, convergence in anthropoids varied little during growth, being unrelated to ontogenetic variation in either relative orbit or interorbit size. Anat Rec, 302:2093–2104, 2019. © 2019 American Association for Anatomy
Pelvic form is hypothesized to reflect locomotor adaptation in anthropoids. Most observed variation is found in the ilium, which traditionally is thought to reflect thoracic and shoulder morphology. This article examines the articulated bony pelvis of anthropoids in three dimensions (3D) to test hypothesized variation in pelvic anatomy related to overall torso form.
Sixty landmarks were collected on articulated pelves from 240 anthropoid individuals. Landmark data were subjected to a Generalized Procrustes Analysis. Principal Components Analysis was used to identify trends among taxa. Linear metrics were extracted, and bivariate allometric analysis was used to compare intergroup differences and scaling trends of specific dimensions.
The combination of 3D and bivariate allometric analysis demonstrates a complex pattern of locomotor/phylogenetic and allometric influences on pelvic morphology. Apes have relatively narrower dorsal interiliac spacing than do most monkeys, with relatively smaller spinal muscle attachment areas but only minimally wider ventral bi‐iliac breadths. Hylobatids and atelids have a relatively more cranial position of their sacra than do other taxa, and hylobatids and cercopithecids relatively more retroflexed ischia. Within groups, the three pelvic joints (lumbosacral, sacroiliac, and hip) become relatively closer together with increasing body size.
A three‐dimensional consideration of the articulated pelvis in anthropoids reveals determinants of pelvic variation not previously appreciated by studies of isolated hipbones. This study provides no support for the hypothesis that the ape pelvis is mediolaterally broader than that of monkeys in relative terms, as would be expected if iliac shape is related to hypothesized differences in thoracic breadth and shoulder orientation. Instead, apes, especially great apes, have relatively narrow sacra and longer lower pelves, related to their shorter, stiffer lumbar spines and torsos. This difference, coupled with strong positive allometry of iliac breadth and negative allometry of key pelvic lengths, along with some variation in ischial morphology in certain taxa, explains much of the variation in pelvic form among anthropoid primates.
- NSF-PAR ID:
- 10051253
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- American Journal of Physical Anthropology
- Volume:
- 166
- Issue:
- 1
- ISSN:
- 0002-9483
- Page Range / eLocation ID:
- p. 3-25
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Among human and nonhuman apes, calcaneal morphology exhibits significant variation that has been related to locomotor behavior. Due to its role in weight‐bearing, however, both body size and locomotion may impact calcaneal morphology. Determining how calcaneal morphologies vary as a function of body size is thus vital to understanding calcaneal functional adaptation. Here, we study calcaneus allometry and relative size in humans (
n = 120) and nonhuman primates (n = 278), analyzing these relationships in light of known locomotor behaviors. Twelve linear measures and three articular facet surface areas were collected on calcaneus surface models. Body mass was estimated using femoral head superoinferior breadth. Relationships between calcaneal dimensions and estimated body mass were analyzed across the sample using phylogenetic least squares regression analyses (PGLS). Differences between humans and pooled nonhuman primates were tested using RMA ANCOVAs. Among (and within) genera residual differences from both PGLS regressions and isometry were analyzed using ANOVAs with post hoc multiple comparison tests. The relationships between all but two calcaneus dimensions and estimated body mass exhibit phylogenetic signal at the smallest taxonomic scale. This signal disappears when reanalyzed at the genus level. Calcaneal morphology varies relative to both body size and locomotor behavior. Humans have larger calcanei for estimated body mass relative to nonhuman primates as a potential adaptation for bipedalism. More terrestrial taxa exhibit longer calcaneal tubers for body mass, increasing the triceps surae lever arm. Among nonhuman great apes, more arboreal taxa have larger cuboid facet surface areas for body mass, increasing calcaneocuboid mobility. -
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Abstract Current approaches to quantify phalangeal curvature assume that the long axis of the bone's diaphysis approximates the shape of a portion of a circle (included angle method) or a parabola (second‐degree polynomial method). Here we developed, tested, and employed an alternative geometric morphometrics‐based (GM) approach to quantify diaphysis shape of proximal phalanges in humans, apes and monkeys with diverse locomotor behaviors. One hundred landmarks of the central longitudinal axis were extracted from 3D surface models and analyzed using 2DGM methods, including generalized Procrustes analyses. Principal components analyses were performed and PC1 scores (>80% of variation) represented the dorsopalmar shape of the bone's central longitudinal axis and separated taxa consistently and in accord with known locomotor behavioral profiles. The most suspensory taxa, including orangutans, hylobatids and spider monkeys, had significantly lower PC1 scores reflecting the greatest amounts of phalangeal curvature. In contrast, bipedal humans and the quadrupedal cercopithecoid monkeys sampled (baboons, proboscis monkeys) exhibited significantly higher PC1 scores reflecting flatter phalanges. African ape (gorillas, chimpanzees and bonobos) phalanges fell between these two extremes and were not significantly different from each other. PC1 scores were significantly correlated with both included angle and the
a coefficient of a second‐degree polynomial calculated from the same landmark dataset, but had a significantly higher correlation with included angles. Our alternative approach for quantifying diaphysis shape of proximal phalanges to investigate dorsopalmar curvature is replicable and does not assume a priori either a circle or parabola model of shape, making it an attractive alternative compared with existing methodologies. -
Cephalopelvic disproportion and its potential impact on human pelvic evolution has been a focus of anthropological research for over 70 years. Recent research on anthropoid primate sexual dimorphism has indicated that obstetric selection may affect multiple primate lineages rather than being a hallmark of the hominin lineage alone. Additionally, the proposed method of selection, mismatch between the size of the cranium and the size of the pelvic canal, implies that the cranium and pelvis may be coevolving and that traits in these two skeletal regions may therefore covary. While covariation between the adult cranium and pelvis has been shown in humans, this has yet to be explored in many non-human primate lineages. Here, we test patterns of covariation between the cranium and pelvis of four genera with different hypothesized levels of cephalopelvic disproportion: Hylobates and Cebus (high cephalopelvic disproportion), Alouatta (low cephalopelvic disproportion), and Lophocebus (expected average cephalopelvic disproportion) using two-block partial least squares analysis. Results indicate high rates of covariation between the cranium and pelvis (r-PLS>0.9, p=0.0001) across all taxa, with bigger pairwise differences among taxa when genera with high cephalopelvic disproportion (Hylobates, Cebus) are compared to genera with low (Alouatta) or average (Lophocebus) cephalopelvic disproportion. This supports the idea that the cranium and pelvis covary and that this relationship may be stronger in lineages with high levels of reported cephalopelvic disproportion. Our results have implications for the role that obstetric selection may have played in shaping cephalopelvic disproportion across multiple anthropoid lineages.more » « less
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Abstract Objectives The function of the browridge in primates is a subject of enduring debate. Early studies argued for a role in resisting masticatory stresses, but recent studies have suggested sexual signaling as a biological role. We tested associations between circumorbital form, diet, oral processing, and social behavior in two species of colobus monkey–the king colobus (
Colobus polykomos ) and western red or bay colobus (Piliocolobus badius ).Materials and methods We quantified circumorbital size and dimorphism in a sample of 98 crania. Controlling for age and facial size, we tested whether variation in circumorbital morphology can be explained by variation in diet, oral processing behavior, masticatory muscle size, and mating system. To contextualize our results, we included a broader sample of facial dimorphism for 67 anthropoid species.
Results Greater circumorbital thickness is unrelated to the stresses of food processing. King colobus engages in longer bouts of anterior tooth use, chews more per ingestive event, and processes a tougher diet, yet circumorbital thickness of
C. polykomos is reduced compared toP. badius . Differences in circumorbital development do not vary with wear or facial size. Greater sexual dimorphism is present inP. badius ; comparisons across anthropoids indicated patterns of circumorbital dimorphism were decoupled from overall size dimorphism.Conclusions The expanded circumorbits of male red colobus monkeys evolved in response to intense male–male competition. This hypothesis is consistent with the pattern across anthropoid primates and highlights the underappreciated role of sexual selection in shaping the primate face.
