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Despite the critical role that the vertebral column plays in postural and locomotor behaviors, the functional morphology of the cervical region (i.e., the bony neck) remains poorly understood, particularly in comparison to that of the thoracic and lumbar sections. This dissertation tests the hypothesis that morphological variation in cervical vertebrae reflects differences in positional behavior (i.e., suspensory vs. nonsuspensory and orthograde vs. pronograde locomotion and postures). Specifically, this project addresses two broad research questions: (1) how does the morphology of cervical vertebrae vary with positional behavior and cranial morphology among primates and (2) where does fossil hominoid morphology fall within the context of the extant primates. Three biomechanical models were developed for the primate cervical spine and their predictions were tested by conducting a comparative analysis using a taxonomically and behaviorally diverse sample of primates. The results of these analyses were used to evaluate fossil hominoid morphology. The two biomechanical models relating vertebral shape to positional behaviors are not supported. However, a number of features distinguish behavioral groups. For example, the angle of the transverse process in relation to the cranial surface of the vertebral body--a trait hypothesized to reflect the deep spinal muscles' ability to extend and stabilize the neck--tends to be greater in pronograde species; this difference is in the opposite of the direction predicted by the biomechanical models. Other traits distinguish behavioral groups (e.g., spinous process length and cross-sectional area), but only in certain parts of the cervical column. The correlation of several vertebral features, especially transverse process length and pedicle cross-sectional area, with anterior cranial length supports the predictions made by the third model that links cervical morphology with head stabilization (i.e., head balancing). Fossil hominoid cervical remains indicate that the morphological pattern that characterizes modern humans was not present in Homo erectus or earlier hominins. These hominins are generally similar to apes in having larger neural arch cross-sectional areas and longer spinous processes than modern humans, likely indicating the presence of comparatively large nuchal muscles. The functional significance of this morphology remains unclear.
ContributorsNalley, Thierra Kénnec (Author) / Kimbel, William H. (Thesis advisor) / Reed, Kaye (Committee member) / Shapiro, Liza (Committee member) / Arizona State University (Publisher)
Created2013
Description
Extremely thick cranial vaults have been noted as a diagnostic characteristic of Homo erectus since the first fossil of the species was identified, but potential mechanisms underlying this seemingly unique trait have not been rigorously investigated. Cranial vault thickness (CVT) is not a monolithic trait, and the responsiveness of its layers to environmental stimuli is unknown. Identifying factors that affect CVT would be exceedingly valuable in teasing apart potential contributors to thick vaults in the Pleistocene. Four hypotheses were tested using CT scans of skulls of more than 1100 human and non-human primates. Data on total frontal, parietal, and occipital bone thickness and bone composition were collected to test the hypotheses: H1. CVT is an allometric consequence of brain or body size. H2. Thick cranial vaults are a response to long, low cranial vault shape. H3. High masticatory stress causes localized thickening of cranial vaults. H4. Activity-mediated systemic hormone levels affect CVT. Traditional comparative methods were used to identify features that covary with CVT across primates to establish behavior patterns that might correlate with thick cranial vaults. Secondly, novel experimental manipulation of a model organism, Mus musculus, was used to evaluate the relative plasticity of CVT. Finally, measures of CVT in fossil hominins were described and discussed in light of the extant comparative and experimental results. This dissertation reveals previously unknown variation among extant primates and humans and illustrates that Homo erectus is not entirely unique among primates in its CVT. The research suggests that it is very difficult to make a mouse grow a thick head, although it can be genetically programmed to have one. The project also identifies a possible hominin synapomorphy: high diploë ratios compared to non-human primates. It also found that extant humans differ from non-human primates in overall pattern of which cranial vault bones are thickest. What this project was unable to do was definitively provide an explanation for why and how Homo erectus grew thick skulls. Caution is required when using CVT as a diagnostic trait for Homo erectus, as the results presented here underscore the complexity inherent in its evolution and development.
ContributorsCopes, Lynn (Author) / Kimbel, William H. (Thesis advisor) / Schwartz, Gary T (Committee member) / Spencer, Mark A. (Committee member) / Ravosa, Matthew J. (Committee member) / Arizona State University (Publisher)
Created2012
Description
Unanswered questions about the evolution of human gender abound and are salient across the anthropological disciplines and beyond. Did adult sex-typed behavioral tendencies actually evolve? If so, when? For what purpose? The best way to gain insight into the evolution of human gender is to understand the evolution and development of sex-typed behavior in comparative primate taxa. Captive research indicates that there are many proximate factors likely to shape the development of sex-typed behavior in non-human primates—prenatal and postnatal endocrinological experience, social experience, ecological factors, and their interactions. However, it is largely unknown how sex-typed behavior proceeds and is shaped by those factors in evolutionarily salient environments. This study investigated one—whether extrinsic sexually differentiated social interactions are likely influential in the development of adult sex-typed behavior in wild-living Lemur catta. Little is known about sex-typed development in this species or in strepsirrhines in general. This research therefore addresses an important phylogenetic gap in our understanding of primate sex-typed development. Behavioral observations were carried out on mixed cross-sectional sample of adult females (n=10), adult males (n=8), yearling females (n=4), yearling males (n=4), and newborn females (n=16) and males (n=14) at Beza Mahafaly Special Reserve in southwest Madagascar from September 2008 to August 2009. Twenty-three sex-typed behaviors were identified in adults using linear mixed effects models and models of group response profiles through time. Of those, only eight had a pre-pubertal developmental component. Infants did not exhibit any sex differences in behavior, but juveniles (prepubertal, weaned individuals) resembled adults in their (relatively few) patterns of expression of sex-typed behavior. Most adult sex-typed behaviors in this species apparently develop at or after puberty and may be under gonadal hormone control. Those that develop before puberty do not likely depend on extrinsic sexually differentiation social interactions for their development, because there is no clear evidence that infants and juvenile male and females are not treated differently by others according to sex. If sexually differentiated social interactions are important for sex-typed behavioral development in subadult ,italic>Lemur catta, they are likely intrinsically (rather than extrinsically) driven.
ContributorsMeredith, Stephanie Lynn (Author) / Nash, Leanne T. (Thesis advisor) / Reed, Kaye E (Committee member) / Schwartz, Gary T (Committee member) / Arizona State University (Publisher)
Created2012
Description
Fundamental hypotheses about the life history, complex cognition and social dynamics of humans are rooted in feeding ecology - particularly in the experiences of young animals as they grow. However, the few existing primate developmental data are limited to only a handful of species of monkeys and apes. Without comparative data from more basal primates, such as lemurs, we are limited in the scope of our understanding of how feeding has shaped the evolution of these extraordinary aspects of primate biology. I present a developmental view of feeding ecology in the ring-tailed lemur (Lemur catta) using a mixed longitudinal sample (infant through adult) collected at the Beza Mahafaly Special Reserve in southwestern Madagascar from May 2009 to March 2010. I document the development of feeding, including weaning, the transition to solid food, and how foods are included in infant diets. Early in juvenility ring-tailed lemurs efficiently process most foods, but that hard ripe fruits and insects require more time to master. Infants and juveniles do not use many of the social learning behaviors that are common in monkeys and apes, and instead likely rely both on their own trial and error and simple local enhancement to learn appropriate foods. Juvenile ring-tailed lemurs are competent and efficient foragers, and that mitigating ecological risks may not best predict the lemur juvenile period, and that increases in social complexity and brain size may be at the root of primate juvenility. Finally, from juvenility through adulthood, females have more diverse diets than males. The early emergence of sex differences in dietary diversity in juvenility that are maintained throughout adulthood indicate that, in addition to reproductive costs incurred by females, niche partitioning is an important aspect of sex differential feeding ecology, and that ontogenetic studies of feeding are particularly valuable to understanding how selection shapes adult, species-typical diets. Overall, lemur juvenility is a time to play, build social relationships, learn about food, and where the kernels of sex-typical feeding develop. This study of the ontogeny of feeding ecology contributes an important phylogenetic perspective on the relationship between juvenility and the emergent foraging behaviors of developing animals
ContributorsO'Mara, Michael Teague (Author) / Nash, Leanne T. (Thesis advisor) / Reed, Kaye E (Committee member) / Schwartz, Gary T (Committee member) / Sauther, Michelle L (Committee member) / Arizona State University (Publisher)
Created2012
Description
Craniofacial morphology in primates can vary on the basis of their diet because foods are often disparate in the amount and duration of force required to break them down. Therefore diet has the potential to exercise considerable selective pressure on the morphology of the masticatory system. The zygomatic arch is a known site of relatively high masticatory strain and yet the relationship between arch form and load type is relatively unknown in primates. While the relative position and robusticity of the arch is considered a key indicator of craniofacial adaptations to a mechanically challenging diet, and central to efforts to infer diet in past species, the relationships between morphology and diet type in this feature are not well established.
This study tested hypotheses using two diet categorizations: total consumption percent and food material properties (FMPs). The first hypothesis that cortical bone area (CA) and section moduli (bone strength) are positively correlated with masticatory loading tests whether CA and moduli measures were greatest anteriorly and decreased posteriorly along the arch. The results found these measures adhered to this predicted pattern in the majority of taxa. The second hypothesis examines sutural complexity in the zygomaticotemporal suture as a function of dietary loading differences by calculating fractal dimensions as indices of complexity. No predictable pattern was found linking sutural complexity and diet in this primate sample, though hard object consumers possessed the most complex sutures. Lastly, cross-sectional geometric properties were measured to investigate whether bending and torsional resistance and cross-sectional shape are related to differences in masticatory loading. The highest measures of mechanical resistance tracked with areas of greatest strain in the majority of taxa. Cross-sectional shape differences do appear to reflect dietary differences. FMPs were not correlated with cross-sectional variables, however pairwise comparisons suggest taxa that ingest foods of greater stiffness experience relatively larger measures of bending and torsional resistance. The current study reveals that internal and external morphological factors vary across the arch and in conjunction with diet in primates. These findings underscore the importance of incorporating these mechanical differences in models of zygomatic arch mechanical behavior and primate craniofacial biomechanics.
This study tested hypotheses using two diet categorizations: total consumption percent and food material properties (FMPs). The first hypothesis that cortical bone area (CA) and section moduli (bone strength) are positively correlated with masticatory loading tests whether CA and moduli measures were greatest anteriorly and decreased posteriorly along the arch. The results found these measures adhered to this predicted pattern in the majority of taxa. The second hypothesis examines sutural complexity in the zygomaticotemporal suture as a function of dietary loading differences by calculating fractal dimensions as indices of complexity. No predictable pattern was found linking sutural complexity and diet in this primate sample, though hard object consumers possessed the most complex sutures. Lastly, cross-sectional geometric properties were measured to investigate whether bending and torsional resistance and cross-sectional shape are related to differences in masticatory loading. The highest measures of mechanical resistance tracked with areas of greatest strain in the majority of taxa. Cross-sectional shape differences do appear to reflect dietary differences. FMPs were not correlated with cross-sectional variables, however pairwise comparisons suggest taxa that ingest foods of greater stiffness experience relatively larger measures of bending and torsional resistance. The current study reveals that internal and external morphological factors vary across the arch and in conjunction with diet in primates. These findings underscore the importance of incorporating these mechanical differences in models of zygomatic arch mechanical behavior and primate craniofacial biomechanics.
ContributorsEdmonds, Hallie Margaret (Author) / Reed, Kaye (Thesis advisor) / Schwartz, Gary (Committee member) / Vinyard, Chris (Committee member) / Arizona State University (Publisher)
Created2017
Description
Within the primate lineage, skeletal traits that contribute to inter-specific anatomical variation and enable varied niche occupations and forms of locomotion are often described as the result of environmental adaptations. However, skeletal phenotypes are more accurately defined as complex traits, and environmental, genetic, and epigenetic mechanisms, such as DNA methylation which regulates gene expression, all contribute to these phenotypes. Nevertheless, skeletal complexity in relation to epigenetic variation has not been assessed across the primate order. In order to gain a complete understanding of the evolution of skeletal phenotypes across primates, it is necessary to study skeletal epigenetics in primates. This study attempts to fill this gap by identifying intra- and inter-specific variation in primate skeletal tissue methylation in order to test whether specific features of skeletal form are related to specific variations in methylation. Specifically, methylation arrays and gene-specific methylation sequencing are used to identify DNA methylation patterns in femoral trabecular bone and cartilage of several nonhuman primate species. Samples include baboons (Papio spp.), macaques (Macaca mulatta), vervets (Chlorocebus aethiops), chimpanzees (Pan troglodytes), and marmosets (Callithrix jacchus), and the efficiencies of these methods are validated in each taxon. Within one nonhuman primate species (baboons), intra-specific variations in methylation patterns are identified across a range of comparative levels, including skeletal tissue differences (bone vs. cartilage), age cohort differences (adults vs. juveniles), and skeletal disease state differences (osteoarthritic vs. healthy), and some of the identified patterns are evolutionarily conserved with those known in humans. Additionally, in all nonhuman primate species, intra-specific methylation variation in association with nonpathological femur morphologies is assessed. Lastly, inter-specific changes in methylation are evaluated among all nonhuman primate taxa and used to provide a phylogenetic framework for methylation changes previously identified in the hominin lineage. Overall, findings from this work reveal how skeletal DNA methylation patterns vary within and among primate species and relate to skeletal phenotypes, and together they inform our understanding of epigenetic regulation and complex skeletal trait evolution in primates.
ContributorsHousman, Genevieve (Author) / Stone, Anne (Thesis advisor) / Quillen, Ellen (Committee member) / Kusumi, Kenro (Committee member) / Stojanowski, Christopher (Committee member) / Arizona State University (Publisher)
Created2017
Description
Skeletal diseases related to reduced bone strength, like osteoporosis, vary in frequency and severity among human populations due in part to underlying genetic differentiation. With >600 disease-associated mutations (DAMs), COL1a1, which encodes the primary subunit of type I collagen, the main structural protein in bone, is most commonly associated with this phenotypic variation. Although numerous studies have explored genotype-phenotype relationships with COL1a1, surprisingly, no study has undertaken an evolutionary approach to determine how changes in constraint over time can be modeled to help predict bone-related disease factors. Here, molecular population and comparative species genetic analyses were conducted to characterize the evolutionary history of COL1a1. First, nucleotide and protein sequences of COL1a1 in 14 taxa representing ~450 million years of vertebrate evolution were used to investigate constraint across gene regions. Protein residues of historically high conservation are significantly correlated with disease severity today, providing a highly accurate model for disease prediction, yet interestingly, intron composition also exhibits high conservation suggesting strong historical purifying selection. Second, a human population genetic analysis of 192 COL1a1 nucleotide sequences representing 10 ethnically and geographically diverse samples was conducted. This random sample of the population shows surprisingly high numbers of amino acid polymorphisms (albeit rare in frequency), suggesting that not all protein variants today are highly deleterious. Further, an unusual haplotype structure was identified across populations, but which is only associated with noncoding variation in the 5' region of COL1a1 where gene expression alteration is most likely. Finally, a population genetic analysis of 40 chimpanzee COL1a1 sequences shows no amino acid polymorphism, yet does reveal an unusual haplotype structure with significantly extended linkage disequilibrium >30 kilobases away, as well as a surprisingly common exon duplication that is generally highly deleterious in humans. Altogether, these analyses indicate a history of temporally and spatially varying purifying selection on not only coding, but noncoding COL1a1 regions that is also reflected in population differentiation. In contrast to clinical studies, this approach reveals potentially functional variation, which in future analyses could explain the observed bone strength variation not only seen within humans, but other closely related primates.
ContributorsStover, Daryn Amanda (Author) / Verrelli, Brian C (Thesis advisor) / Dowling, Thomas E (Committee member) / Rosenberg, Michael S. (Committee member) / Stone, Anne C (Committee member) / Schwartz, Gary T (Committee member) / Arizona State University (Publisher)
Created2010
Description
The bony pelvis is a pivotal component of the locomotor system, as it links the hindlimb with the trunk and serves as anchorage for the primary propulsive musculature. Its shape is therefore expected to be adapted to the biomechanical demands of habitual locomotor behavior. However, because the relationship between locomotor mechanics and pelvic morphology is not well understood, the adaptive significance of particular pelvic traits and overall pelvic shape remains unclear. This study used an integrative, dual approach to elucidate the relationship between form and function in the primate pelvis. A biomechanical cylinder model of pelvic stress resistance was tested using in vitro strain analysis of monkey and ape cadaver specimens. These results were used to refine adaptive hypotheses relating pelvic form to locomotor mechanics. Hypotheses of adaptation were then tested via univariate and geometric morphometric methods using a taxonomically broad, comparative sample of 67 primate taxa. These results suggest that the pelvis exhibits some iliac and ischial adaptations to stress resistance that are associated with the biomechanical demands of habitual locomotor loading and of body size. The ilium and ischium exhibit relatively low levels of strain during experimental loading as well as adaptations that increase strength. The pubis exhibits relatively high strains during loading and does not vary as predicted with locomotion. This integrated study clarifies the relationship between strain and adaptation; these results support the hypothesis that bones adapted to stress resistance exhibit low strains during typical loading. In general, the cylinder model of pelvic biomechanics is unsupported. While the predictions of loading regimes were generally rejected, the inability of these methods to test the possible occurrence of overlapping loading regimes precludes outright rejection of the cylinder model. However, the lack of support for predicted global responses to applied loading regimes suggests that pelvic stress resistance may be better explained by a model that accounts for local, functional subunits of pelvic structure. The coalescence of a localized model of pelvic biomechanics and comparative morphometrics has great potential to shed light on the evolution of the complex, multi-functional structure of the pelvis.
ContributorsLewton, Kristi Lynn (Author) / Spencer, Mark A. (Thesis advisor) / Reed, Kaye E (Committee member) / Schwartz, Gary T (Committee member) / Ward, Carol V. (Committee member) / Arizona State University (Publisher)
Created2010