Matching Items (12)

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The Hominin Sites and Paleolakes Drilling Project: inferring the environmental context of human evolution from eastern African rift lake deposits

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The role that climate and environmental history may have played in influencing human evolution has been the focus of considerable interest and controversy among paleoanthropologists for decades. Prior attempts to

The role that climate and environmental history may have played in influencing human evolution has been the focus of considerable interest and controversy among paleoanthropologists for decades. Prior attempts to understand the environmental history side of this equation have centered around the study of outcrop sediments and fossils adjacent to where fossil hominins (ancestors or close relatives of modern humans) are found, or from the study of deep sea drill cores. However, outcrop sediments are often highly weathered and thus are unsuitable for some types of paleoclimatic records, and deep sea core records come from long distances away from the actual fossil and stone tool remains. The Hominin Sites and Paleolakes Drilling Project (HSPDP) was developed to address these issues. The project has focused its efforts on the eastern African Rift Valley, where much of the evidence for early hominins has been recovered. We have collected about 2 km of sediment drill core from six basins in Kenya and Ethiopia, in lake deposits immediately adjacent to important fossil hominin and archaeological sites. Collectively these cores cover in time many of the key transitions and critical intervals in human evolutionary history over the last 4 Ma, such as the earliest stone tools, the origin of our own genus Homo, and the earliest anatomically modern Homo sapiens. Here we document the initial field, physical property, and core description results of the 2012–2014 HSPDP coring campaign.

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  • 2016-02-19

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Climate and Species Richness Predict the Phylogenetic Structure of African Mammal Communities

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We have little knowledge of how climatic variation (and by proxy, habitat variation) influences the phylogenetic structure of tropical communities. Here, we quantified the phylogenetic structure of mammal communities in

We have little knowledge of how climatic variation (and by proxy, habitat variation) influences the phylogenetic structure of tropical communities. Here, we quantified the phylogenetic structure of mammal communities in Africa to investigate how community structure varies with respect to climate and species richness variation across the continent. In addition, we investigated how phylogenetic patterns vary across carnivores, primates, and ungulates. We predicted that climate would differentially affect the structure of communities from different clades due to between-clade biological variation. We examined 203 communities using two metrics, the net relatedness (NRI) and nearest taxon (NTI) indices. We used simultaneous autoregressive models to predict community phylogenetic structure from climate variables and species richness. We found that most individual communities exhibited a phylogenetic structure consistent with a null model, but both climate and species richness significantly predicted variation in community phylogenetic metrics. Using NTI, species rich communities were composed of more distantly related taxa for all mammal communities, as well as for communities of carnivorans or ungulates. Temperature seasonality predicted the phylogenetic structure of mammal, carnivoran, and ungulate communities, and annual rainfall predicted primate community structure. Additional climate variables related to temperature and rainfall also predicted the phylogenetic structure of ungulate communities. We suggest that both past interspecific competition and habitat filtering have shaped variation in tropical mammal communities. The significant effect of climatic factors on community structure has important implications for the diversity of mammal communities given current models of future climate change.

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  • 2015-04-15

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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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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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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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Stable isotope analysis of archaeological and modern micromammals from the Greater Cape Floristic Region near Pinnacle Point, on the south coast of South Africa

Description

The Middle Stone Age archaeological record from the south coast of South Africa contains significant evidence for early modern human behavior. The south coast is within the modern Greater Cape

The Middle Stone Age archaeological record from the south coast of South Africa contains significant evidence for early modern human behavior. The south coast is within the modern Greater Cape Floristic Region (GCFR), which in the present-day encompasses the entirety of South Africa’s Winter Rainfall Zone (WRZ) and contains unique vegetation elements that have been hypothesized to be of high utility to hunter-gatherer populations. Extant paleoenvironmental proxy records for the Pleistocene in the region often indicate evidence for more open environments during the past than occur in the area in the present-day, while climate models suggest glacial presence of the WRZ that would support maintenance of C3-predominant GCFR vegetation.

These paleoenvironmental proxies sample past environments at geographic scales that are often regional. The GCFR flora is hyper-diverse, and glacial climate change-driven impacts on local vegetation could have been highly variable over relatively small geographic scales. Proxy records that are circumscribed in their geographic scale are thus key to our understanding of ancient environments at particular MSA archaeological localities.

Micromammal fossil teeth are now recognized as an abundant potential reservoir of paleoenvironmental proxy data at an extremely local scale. This study analyzed modern micromammal teeth obtained from raptor pellets at three locations on the south coast. Stable carbon isotope analysis indicates that the modern micromammals from the taxa sampled consume a wide range of δ13Cplant on the landscape when it is available, and thus stable carbon isotope analysis of micromammal teeth should act as a proxy for the range of available δ13Cdiet in a circumscribed area of vegetation.

Micromammal stable carbon isotope data obtained from specimens from one of the few well-dated MIS6-MIS5 sequences in the region (Pinnacle Point sites 13B, 30, and 9C). δ13Cenamel values for the taxa sampled indicate diets that are primarily C3, and there is almost no evidence for a dietary C4 grass component in any of the sampled specimens. This indicates that, at a minimum, pockets of C3 vegetation associated with the GCFR were likely available to hunter-gatherers at Pinnacle Point throughout the Middle and Late Pleistocene.

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  • 2015

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

Description

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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  • 2020

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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  • 2017

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Tephrostratigraphy of Pliocene Drill Cores from Kenya and Ethiopia, and Pleistocene Exposures in the Ledi-Geraru Research Project Area, Ethiopia: Geological Context for the Evolution of Australopithecus and Homo

Description

East African extensional basins have played a crucial role in revealing the evolution and characteristics of the early stages of continental rifting and for providing the geological context of hominin

East African extensional basins have played a crucial role in revealing the evolution and characteristics of the early stages of continental rifting and for providing the geological context of hominin evolution and innovation. The numerous volcanic eruptions, rapid sedimentation and burial, and subsequent exposure through faulting and erosion, provide excellent conditions for the preservation of tectonic history, paleoenvironment data, and vertebrate fossils. The reconstruction of depositional environments and provision of geochronologic frameworks for hominin sites have been largely provided by geologic investigations in conjunction with paleontological studies, like the Ledi-Geraru Research Project (LGRP). High-resolution paleoclimate records that can be directly linked to hominin fossil outcrops have been developed by the Hominin Sites and Paleolakes Drilling Project (HSPDP) which collected sedimentary-paleolake cores at or near key hominin fossil sites.

Two chapters of this dissertation are a result of research associated with the HSPDP. For HSPDP, I establish a tephrostratigraphic framework for the drill cores from the Northern Awash (Afar, Ethiopia) and Baringo-Tugen Hills-Barsemoi (Kenya) HSPDP sites. I characterize and fingerprint tephra through glass shard and feldspar phenocryst geochemistry. From tephra geochemical analyses, I establish chronostratigraphic ties between the HSPDP cores’ high-resolution paleoclimate records to outcrop stratigraphy which are associated with hominin fossils sites.

Three chapters of this dissertation are a result of field work with the LGRP. I report new geological investigations (stratigraphic, tectonic, and volcanic) of two previously unmapped regions from the eastern Ledi-Geraru (ELG), Asboli and Markaytoli. Building upon this research I present interpretations from tephra analyses, detailed stratigraphic analyses, and geologic mapping, of the Pleistocene (~2.6 to < 2.45 Ma) basin history for the LGRP. My work with the LGRP helps to reconstruct a more complete Early Pleistocene depositional and geologic history of the lower Awash Valley.

Overall, this dissertation contributes to the reconstruction of hominin paleoenvironments and the geochronological framework of the Pliocene and Pleistocene faunal/hominin records. It further contributes to rift basin history in East Africa by elaborating the later structural and stratigraphic history of the lower Awash region.

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Date Created
  • 2019