Matching Items (9)

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Lemur Biorhythms and Life History Evolution

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Skeletal histology supports the hypothesis that primate life histories are regulated by a neuroendocrine rhythm, the Havers-Halberg Oscillation (HHO). Interestingly, subfossil lemurs are outliers in HHO scaling relationships that have

Skeletal histology supports the hypothesis that primate life histories are regulated by a neuroendocrine rhythm, the Havers-Halberg Oscillation (HHO). Interestingly, subfossil lemurs are outliers in HHO scaling relationships that have been discovered for haplorhine primates and other mammals. We present new data to determine whether these species represent the general lemur or strepsirrhine condition and to inform models about neuroendocrine-mediated life history evolution. We gathered the largest sample to date of HHO data from histological sections of primate teeth (including the subfossil lemurs) to assess the relationship of these chronobiological measures with life history-related variables including body mass, brain size, age at first female reproduction, and activity level. For anthropoids, these variables show strong correlations with HHO conforming to predictions, though body mass and endocranial volume are strongly correlated with HHO periodicity in this group. However, lemurs (possibly excepting Daubentonia) do not follow this pattern and show markedly less variability in HHO periodicity and lower correlation coefficients and slopes. Moreover, body mass is uncorrelated, and brain size and activity levels are more strongly correlated with HHO periodicity in these animals. We argue that lemurs evolved this pattern due to selection for risk-averse life histories driven by the unpredictability of the environment in Madagascar. These results reinforce the idea that HHO influences life history evolution differently in response to specific ecological selection regimes.

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  • 2015-08-12

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The Evolution of Human Cervical Lordosis

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Many of the derived features of the human skeleton can be divided into two adaptive suites: traits related to bipedalism and traits related to encephalization. The cervical spine connects these

Many of the derived features of the human skeleton can be divided into two adaptive suites: traits related to bipedalism and traits related to encephalization. The cervical spine connects these adaptive suites and is itself unique in its marked lordosis. I approach human cervical evolution from three directions: the functional significance of cervical curvature, the identification of cervical lordosis in osteological material, and the representation of the cervical spine in the hominin fossil record.

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  • 2014-05

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The roles of positional behavior and brain growth in generating ontogenetic variation in the human cranial base

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Previous studies have demonstrated that cranial base anatomy is influenced primarily by three different characteristics: brain shape, positional behavior, and facial growth (Lieberman et al. 2000). Although the timing of

Previous studies have demonstrated that cranial base anatomy is influenced primarily by three different characteristics: brain shape, positional behavior, and facial growth (Lieberman et al. 2000). Although the timing of cranial base growth is not fully understood, features of the cranial base are frequently used to interpret the hominin fossil record (Guy et al. 2005; White et al. 1994; Brunet et al. 2002). While specific aspects of cranial base morphology may be species-specific, there is sparse information on the developmental mechanisms driving these adult morphologies. The aim of this study is to 1) examine changes in the human cranial base form throughout ontogeny and 2) determine their relationship to the development of positional behavior and brain growth. This research asks: to what extent does human cranial base morphology vary before and after adult positional behavior is acquired? The null hypothesis is that there is no relationship between features of the cranial base and the development of positional behavior. Data are collected using 3D landmarks on n=35 human crania and analyzed with both Morphologika (O'Higgins and Jones 1999) and MorphoJ (Klingenberg 2011) to identify age related changes in shape. Results of this study demonstrate that most of the changes in cranial base form occur between dental eruption stages N and NJ1 between 0 and 2 years of age. These changes consist of a relative shortening of the anterior-posterior cranial base length, a more posterior positioning of the foramen magnum, and a more anterior position of the occipital condyles and separate the N and NJ1 dental development groups from other groups. This change coincides with the transition to upright posture in human children (Abitbol 1993), a significant period of brain growth (Neubauer 2009) and has implications for reconstructing positional behavior in fossil hominins. Despite new insights into the development of cranial base morphology, the utility of the cranial base in assigning hominin taxonomy remains inconclusive.

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  • 2015-05

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Analysis of Native American Scalping from the Chavez Pass Population

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Scalping has been practiced by the Native Americans since pre-Columbian times in North America and is observed as cut-marks in the form of a rough circle on the superior aspect

Scalping has been practiced by the Native Americans since pre-Columbian times in North America and is observed as cut-marks in the form of a rough circle on the superior aspect of the cranium of the individual. For this study, there are 7 crania with cut-marks evident of scalping from the Southwest population of Chavez Pass. These crania were excavated from the site of Nuvakwewtaqa located in north-central Arizona, in the middle of the Coconino National Forest. Unfortunately, the site was heavily looted through pot-hunter activity, leading to a large collection of commingle remains. The objectives of this study are summarized into three basic question words: Who? Where? And, How? More specifically: [1] whether there is a relationship between age or sex and being a victim of scalping; [2] whether there is a relationship between the burial location and having been scalped; and, [3] whether the age or sex of an individual affected the manner in which they were scalped. For this analysis of scalping, three statistical tests were used: Fisher's exact test, Chi-Square test and two-sample t-tests.

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Date Created
  • 2014-05

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Morphological and Development Analysis of Teeth Recovered from an Archaeological Teratoma

Description

Teratomas are germ cell tumors that can generate a broad spectrum of biological tissues including: hair, oil glands, bones, and teeth. Little research has focused on the detailed comparison of

Teratomas are germ cell tumors that can generate a broad spectrum of biological tissues including: hair, oil glands, bones, and teeth. Little research has focused on the detailed comparison of teeth from growing within teratomas to teeth that grew normally within the oral cavity. Broad similarities in the overall pattern of dental growth have previously been observed using average enamel thickness, a measurement of enamel height, comparisons. Enamel thickness is used to infer functional aspects of dentition. Relative enamel thickness values have not been used in previous studies to account for the difference in size of the teeth.

ASU’s Bioarchaeology of Nubia Expedition (BONE) led by Dr. Brenda Baker discovered the remains of a female individual from the Classic Kerma period with a preserved large teratoma containing hard tissue components including two molariform teeth. There are only three previous recorded instances of teratomas in a paleopathological setting.

This study analyzed the characteristics of teeth found within a teratoma and compared them to permanent oral dentition to ascertain the degree to which dental development is affected by local growth environment. Permanent (oral) molars from multiple individuals and 2 teratoma teeth from a singular individual from the BONE site were analyzed alongside a comparative sample of permanent (oral) molars from an unrelated, more modern population. MicroCT scans were used to create digital renditions of the teeth to create 3D and 2D models to analyze the enamel and dentine of the teeth to measure their morphological characteristics. The relative enamel thickness and the absolute occlusal enamel volumes were calculated. The study found that there are significant differences in enamel thickness between the teratoma teeth and any of its oral cavity counterparts.

This study is unique in that it is the first study to analyze teeth from a teratoma to permanent teeth from the oral cavity using 2D and 3D digital dental models created from microCT data. It is also the first study to analyze these morphological characteristics in an archaeological sample.

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  • 2019-12

The functional morphology of the primate zygomatic arch in relation to diet

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

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.

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Date Created
  • 2017

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A dental topographic analysis of deciduous tooth wear in hominoids

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Early weaning, slow somatic and dental growth, and late age at reproduction are all part of a suite of energetic trade-offs that have shaped human evolution. A similar suite of

Early weaning, slow somatic and dental growth, and late age at reproduction are all part of a suite of energetic trade-offs that have shaped human evolution. A similar suite of energetic trade-offs has shaped the evolution of the indriid-palaeopropithecid clade, though members of this clade exhibit extremely fast dental development and nearly vestigial deciduous teeth. The development and functional occlusion of the primary postcanine dentition (i.e., deciduous premolars and molars) coincides with several life history parameters in great apes and indriids. This dissertation explored great ape dental macrowear, molar development in indriids, and molar size in lemurs with a broader goal of improving reconstructions of life history profiles in extinct primates. To this aim, macrowear and dental development were analyzed in apes and lemurs, respectively. Occlusal casts (six great ape species; N=278) were scanned to track mandibular fourth deciduous premolar (dp4) macrowear. Utilizing dental topographic analyses, changes in occlusal gradient and terrain were quantified. A subset of the great ape data (four species; n=199) was analyzed to test if differences in dp4 wear correlate with age at weaning. Using dental histology, molar development was reconstructed for Indri indri (n=1) and Avahi laniger (n=1). Life history and molar size data were collected from the literature. The results of this dissertation demonstrate that most great apes exhibited evidence of topographic maintenance, suggesting dp4s wear in a manner that maintain functional efficiency during growth and development; however, the manner in which maintenance is achieved (e.g., preservation of relief or complexity) is species specific. Dp4 macrowear is not correlated with age at weaning in great apes and is probably unreliable to reconstruct age at weaning in hominins. The pace of molar development in members of the indriid- palaeopropithecid clade did not correlate with body or brain size, an association present in several other primates. Associations of molar size with age at weaning suggest that expanding other developmental models (e.g., the inhibitory cascade) to life history is worth consideration. The broad variation in macrowear, dental development, and size highlights how the primary dentition may correlate with different life history parameters depending on the species and ecological setting, an important consideration when using teeth to reconstruct life history profiles.

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Date Created
  • 2016

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Form and function of the primate cervical vertebral column

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As the junction between the head and the trunk, the neck functions in providing head stability during behaviors like feeding to facilitating head mobility during behavior like grooming and predator

As the junction between the head and the trunk, the neck functions in providing head stability during behaviors like feeding to facilitating head mobility during behavior like grooming and predator vigilance. Despite its importance to these vital behaviors, its form and function remain poorly understood. Fossil hominin cervical vertebrae preserve a striking diversity in form despite the commitment to orthograde bipedality. Do these differences in cervical vertebral form correspond to functional variations among our recent ancestors? This dissertation attempts to understand 1) how does the neck function in head stability and mobility 2) how do these functions relate to cervical vertebral form. Kinematic and passive range of motion studies were conducted in several species of primate to obtain measures of function which were subsequently related to skeletal form.

Results show that cervical vertebral morphology does not significantly covary with differences in joint mobility. Rather, they implicate the critical role of ligaments and muscles in facilitating head mobility. Results of the kinematics study show that the neck plays a role in maintaining head stability during locomotion. However, the kinematic data do not significantly correlate with morphological variation among primate species. Given the negative results of the extant morphological analyses, it is difficult to apply them to the fossil record. As such, the functional significance of the disparate morphologies found in the hominin fossil record remain ambiguous.

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Date Created
  • 2019

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Variation in dental morphology and bite force along the tooth row in anthropoids

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Modern primate diet is well-studied because of its considerable influence on multiple aspects of morphology, including the shape of the facial skeleton and teeth. It is well-established that differences in

Modern primate diet is well-studied because of its considerable influence on multiple aspects of morphology, including the shape of the facial skeleton and teeth. It is well-established that differences in craniofacial form influence feeding abilities by altering the nature of bite force production. Tooth morphology, likewise, has been shown to vary with diet across primates, particularly in the details of occlusal form. It has also been suggested that tooth form (e.g., tooth root size and shape and crown size) reflects, in part, the demands of resisting the stresses generated during feeding. However, while they are central to our efforts to infer diet in past species, the relationships between bite force production, craniofacial morphology and tooth form are not well-established. The current study is separated into two parts. In Part I, the hypothesis that crown size and root surface area are adapted to resist masticatory stress is evaluated by testing whether these features show correlated variation along the tooth row in a taxonomically diverse sample of primates. To further explore the adaptive nature of this correlation, pair-wise comparisons between primates with mechanically resistant diets and closely-related species consuming less resistant foods are performed. If crown size and root surface area covary along the tooth row, past research suggests they may be related to bite force. To test this hypothesis, Part II examines the variation of these dental characteristics in comparison to theoretically-derived bite force patterns along the tooth row. Results suggest that patterns of maximum bite force magnitude along the tooth row are variable both within and between species, underscoring the importance of individual craniofacial variation on masticatory force production. Furthermore, it is suggested that some adaptations traditionally associated with high bite force production (i.e., facial orthognathy) may increase anterior biting force at the expense of posterior biting force. Taken together, results from the current study reveal that both tooth root and crown size vary in conjunction with the mechanical properties of diet and with bite force patterns along the tooth row in anthropoids.

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Date Created
  • 2012