Matching Items (21)

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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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Environmental Impacts on Light Stable Isotope Systems

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Isotopic analyses of archaeological and modern materials are commonly used to reconstruct diet, climate, and habitat. This study analyzes 15 camelid samples from three sites (two archaeological, one modern) in

Isotopic analyses of archaeological and modern materials are commonly used to reconstruct diet, climate, and habitat. This study analyzes 15 camelid samples from three sites (two archaeological, one modern) in South America to determine their carbon and nitrogen isotopic values to further explore the relationship between stable isotopes and environments. Camelid individuals in the modern site of Cuenca, Ecuador had a diet of almost entirely C3 vegetation, while those in Chen Chen, Peru had slightly higher values, still consistent with C3 plants. Those in the higher altitude site of Pumapunku, Bolivia had higher δ13C values than expected, indicating they may have been foddered with a mixed diet. These isotopic data indicate that vegetation, and therefore herbivore diets, are influenced by altitude. Additionally, it was found that a positive linear relationship exists between δ15N values and aridity of a site. Results indicate that aspects of the environment such as aridity are reflected in isotopic signatures. These results contribute to the increasing amount of data on isotopic variation in South American camelids, both modern and archaeological.

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  • 2016-05

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Identifying the Lagomorphs of 111 Ranch

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This study was conducted in order to determine whether the lagomorphs of 111 Ranch- Aztlanolagus agilis, Hypolagus arizonensis, and Sylvilagus cunicularius- could be distinguished based on femora. This is because

This study was conducted in order to determine whether the lagomorphs of 111 Ranch- Aztlanolagus agilis, Hypolagus arizonensis, and Sylvilagus cunicularius- could be distinguished based on femora. This is because while there is a large quantity of disarticulated lagomorph postcranial fossils from 111 Ranch, the chief diagnostic traits of A. agilis and H. arizonensis are the enamel patterns on their third premolars, leaving a large swath of specimens unidentifiable by diagnostic traits alone. Specimens from the Arizona Museum of Natural History were measured and compared to specimens known to be from these genera. Additionally, morphological traits in mandibles were used to identify mandible specimens, which in turn were used to identify fossils with the same specimen label. Statistical tests such as t-tests and principal components analyses were used to examine the distributions of sizes and locate clusters of datapoints likely corresponding to each genus. Some of these could be linked to a genus based on one particular specimen, P15156, which had been identified as Hypolagus based on its mandible morphology and size. The majority of the Museum'a specimens were thus associated with one of the three species, save for those which were too damaged and intermediate in size to confidently categorize.

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  • 2019-05

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Positional behaviors and the neck: a comparative analysis of the cervical vertebrae of living primates and fossil hominoids

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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

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.

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  • 2013

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Tracking climate-driven changes in Neandertal subsistence behaviors and prey mobility patterns

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The ability of Neandertals to cope with the oscillating climate of the late Pleistocene and the extent to which these climate changes affected local Neandertal habitats remain unanswered anthropological topics

The ability of Neandertals to cope with the oscillating climate of the late Pleistocene and the extent to which these climate changes affected local Neandertal habitats remain unanswered anthropological topics of considerable scientific interest. Understanding the impact of climatic instability on Neandertals is critical for reconstructing the behaviors of our closest fossil relatives and possibly identifying factors that contributed to their extinction. My work aimed to test the hypotheses that 1) cold climates stressed Neandertal populations, and 2) that global climate changes affected local Neandertal habitats. An analysis of Neandertal butchering on Cervus elaphus, Rangifer tarandus, and Capreolus capreolus skeletal material deposited during global warm and cold phases from two French sites - Pech de l'Azé IV and Roc de Marsal - was conducted to assess the impact of climate change on butchering strategies and resource extraction. Results from a statistical analysis of surface modification on all marrow yielding long bones, including the 1st phalanx, demonstrated that specimens excavated from the cold levels at each cave have more cut marks (Wald χ2= 51.33, p= <0.001) and percussion marks (Wald χ2= 4.92, p= 0.02) than specimens from the warm levels after controlling for fragment size. These results support the hypothesis that Neandertals were nutritionally stressed during glacial cycles. The hypothesis that global climates affected local habitats was tested through radiogenic strontium isotopic reconstruction of large herbivore mobility patterns (e.g., Bison, Equus, Cervus and Rangifer), because it is known that in the northern hemisphere, mammals migrate less in warm, well-vegetated environments, but more in cold, open environments. Identifying isotopic variation in mammalian fossils enables mobility patterns to be inferred, providing an indication of whether environments at Pech de l'Azé IV and Roc de Marsal tracked global climates. Results from this study indicate that Neandertal prey species within the Dordogne Valley of France did not undertake long distance round-trip migrations in glacial or interglacial cycles, maintaining the possibility that local habitats did not change in differing climatic cycles. However, because Neandertals were nutritionally stressed the most likely conclusion is that glacial cycles decreased herbivore populations, thus stressing Neandertals.

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Date Created
  • 2012

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The role of ochre in the development of modern human behavior: a case study from South Africa

Description

In recent years, southern Africa has figured prominently in the modern human origins debate due to increasing evidence for precocious behaviors considered to be unique to our species. These significant

In recent years, southern Africa has figured prominently in the modern human origins debate due to increasing evidence for precocious behaviors considered to be unique to our species. These significant findings have included bone tools, shell beads, engraved ostrich eggshell, and heavily ground and engraved ochre fragments. The presence of ochre in Middle Stone Age (MSA, ~250-40kya) archaeological sites in southern Africa is often proposed as indirect evidence for the emergence of symbolic or artistic behavior, a uniquely modern human trait. However, there is no remaining artwork from this period and there is significant debate about what the ochre may have been used for. With a few exceptions, ochre has gone largely unstudied. This project tested competing models for ochre use within the Pinnacle Point (PP), South Africa research area. Combined results from characterization and sourcing analyses, color classification, heat treatment analysis, and hafting experiments suggest MSA ochre is tied to early symbolic or ritual behavior.

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Date Created
  • 2012

A semiotic approach to the evolution of symboling capacities during the late Pleistocene with implications for claims of modernity in early human groups

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This research uses Peircean Semiotics to model the evolution of symbolic behavior in the human lineage and the potential material correlates of this evolutionary process in the archaeological record. The

This research uses Peircean Semiotics to model the evolution of symbolic behavior in the human lineage and the potential material correlates of this evolutionary process in the archaeological record. The semiotic model states the capacity for symbolic behavior developed in two distinct stages. Emergent capacities are characterized by the sporadic use of non-symbolic and symbolic material culture that affects information exchange between individuals. Symbolic exchange will be rare. Mobilized capacities are defined by the constant use of non-symbolic and symbolic objects that affect both interpersonal and group-level information exchange. Symbolic behavior will be obligatory and widespread. The model was tested against the published archaeological record dating from ~200,000 years ago to the Pleistocene/Holocene boundary in three sub-regions of Africa and Eurasia. A number of Exploratory and Confirmatory Data Analysis techniques were used to identify patterning in artifacts through time consistent with model predictions. The results indicate Emergent symboling capacities were expressed as early as ~100,000 years ago in Southern Africa and the Levant. However, capacities do not appear fully Mobilized in these regions until ~17,000 years ago. Emergent symboling is not evident in the European record until ~42,000 years ago, but develops rapidly. The results also indicate both Anatomically Modern Humans and Neanderthals had the capacity for symbolic behavior, but expressed those capacities differently. Moreover, interactions between the two populations did not select for symbolic expression, nor did periodic aggregation within groups. The analysis ultimately situates the capacity for symbolic behavior in increased engagement with materiality and the ability to recognize material objects can be made meaningful– an ability that must have been shared with Anatomically Modern Humans’ and Neanderthals’ most recent common ancestor. Consequently, the results have significant implications for notions of ‘modernity’ and human uniqueness that drive human origins research. This work pioneers deductive approaches to cognitive evolution, and both strengths and weaknesses are discussed. In offering notable results and best practices, it effectively operationalizes the semiotic model as a viable analytical method for human origins research.

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Date Created
  • 2016

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A dental topographic analysis of deciduous tooth wear in hominoids

Description

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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  • 2016

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Hominin Dietary Niche Breadth Expansion During Pliocene Environmental Change in Eastern Africa

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Stable carbon isotope data for early Pliocene hominins Ardipithecus ramidus and Australopithecus anamensis show narrow, C3-dominated isotopic signatures. Conversely, mid-Pliocene Au. afarensis has a wider isotopic distribution and consumed both

Stable carbon isotope data for early Pliocene hominins Ardipithecus ramidus and Australopithecus anamensis show narrow, C3-dominated isotopic signatures. Conversely, mid-Pliocene Au. afarensis has a wider isotopic distribution and consumed both C3 and C4 plants, indicating a transition to a broader dietary niche by ~ 3.5 million years ago (Ma). Dietary breadth is an important aspect of the modern human adaptive suite, but why hominins expanded their dietary niche ~ 3.5 Ma is poorly understood at present. Eastern Africa has produced a rich Pliocene record of hominin species and associated mammalian faunas that can be used to address this question. This dissertation hypothesizes that the shift in hominin dietary breadth was driven by a transition to more open and seasonal environments in which food resources were more patchily distributed both spatially and temporally. To this end, I use a multiproxy approach that combines hypsodonty, mesowear, faunal abundance, and stable isotope data for temporally well-constrained early and mid-Pliocene mammal assemblages (5.3-2.95 Ma) from Ethiopia, Kenya, and Tanzania to infer patterns of environmental change through time. Hypsodonty analyses revealed that early Pliocene sites had higher annual precipitation, lower precipitation seasonality, and lower temperature seasonality than mid-Pliocene sites. Mesowear analyses, however, did not show from attrition- to abrasion- dominated wear through time. Abundance data suggest that there was a trend towards aridity, as Tragelaphini (woodland antelope) decline while Alcelaphini (grassland antelope) increased in abundance through time. Carbon isotope data indicate that most taxa shifted to diets focusing on C4 grasses through time, which closely follows paleosol carbon isotope data documenting the expansion of grassland ecosystems in eastern Africa. Overall, the results suggest Ar. ramidus and Au. anamensis preferentially exploited habitats in which preferred food resources were likely available year-round, whereas Au. afarensis lived in more variable, seasonal environments in which preferred foods were available seasonally. Au. afarensis and K. platyops likely expanded their dietary niche in less stable environments, as reflected in their wider isotopic niche breadth.

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Date Created
  • 2020

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Abiotic and Biotic Drivers of Turnover and Community Assembly in African Mammals

Description

Climate and environmental forcing are widely accepted to be important drivers of evolutionary and ecological change in mammal communities over geologic time scales. This paradigm has been particularly influential in

Climate and environmental forcing are widely accepted to be important drivers of evolutionary and ecological change in mammal communities over geologic time scales. This paradigm has been particularly influential in studies of the eastern African late Cenozoic fossil record, in which aridification, increasing seasonality, and C4 grassland expansion are seen as having shaped the major patterns of human and faunal evolution. Despite the ubiquity of studies linking climate and environmental forcing to evolutionary and ecological shifts in the mammalian fossil record, many central components of this paradigm remain untested or poorly developed. To fill this gap, this dissertation employs biogeographical and macroecological analyses of present-day African mammal communities as a lens for understanding how abiotic change may have shaped community turnover and structure in the eastern African Plio-Pleistocene. Three dissertation papers address: 1) the role of ecological niche breadth in shaping divergent patterns of macroevolutionary turnover across clades; 2) the effect of climatic and environmental gradients on community assembly; 3) the relative influence of paleo- versus present-day climates in structuring contemporary patterns of community diversity. Results of these papers call into question many tenets of current theory, particularly: 1) that niche breadth differences (and, by extension, their influence on allopatric speciation) are important drivers of macroevolution, 2) that climate is more important than biotic interactions in community assembly, and 3) that communities today are in equilibrium with present-day climates. These findings highlight the need to critically reevaluate the role and scale-dependence of climate in mammal evolution and community ecology and to carefully consider potential time lags and disequilibrium dynamics in the fossil record.

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Date Created
  • 2018