Matching Items (12)

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

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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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  • 2018

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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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  • 2012

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Biomechanical Constraints on Molar Emergence in Primates

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Across primates, molar-emergence age is strongly correlated to life-history variables, such as age-at-first-reproduction and longevity. This relationship allows for the reconstruction of life-history parameters in fossil primates. The mechanism responsible

Across primates, molar-emergence age is strongly correlated to life-history variables, such as age-at-first-reproduction and longevity. This relationship allows for the reconstruction of life-history parameters in fossil primates. The mechanism responsible for modulating molar-emergence age is unknown, however. This dissertation uses a biomechanical model that accurately predicts the position of molars in adults to determine whether molar emergence is constrained by chewing biomechanics throughout ontogeny. A key aspect of chewing system configuration in adults is the position of molars: the distal-most molar is constrained to avoid tensile forces at the temporomandibular joint (TMJ). Using three-dimensional data from growth samples of 1258 skulls, representing 21 primate species, this research tested the hypothesis that the location and timing of molar emergence is constrained to avoid high and potentially dangerous tensile forces at the TMJ throughout growth. Results indicate that molars emerge in a predictable position to safeguard the TMJ during chewing. Factors related to the size of the buffer zone, a safety feature that creates greater stability at the TMJ during biting, account for a large portion of both ontogenetic and interspecific variation in the position of emergence. Furthermore, the rate at which space is made available in the jaws and the duration of jaw growth both determine the timing of molar emergence. Overall, this dissertation provides a mechanical and developmental model for explaining temporal and spatial variation in molar emergence and a framework for understanding how variation in the timing of molar emergence has evolved among primates. The findings suggest that life history is related to ages at molar emergence through its influence on the rate and duration of jaw growth. This dissertation provides support for the functionally integrated nature of craniofacial growth and has implications for the study of primate life history evolution and masticatory morphology in the fossil record.

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  • 2017

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Evolution and paleoecology of Pliocene Suidae (Artiodactyla, Mammalia) in the lower Awash Valley (Afar, Ethiopia): implications for hominin evolution and paleoenvironments

Description

Providing an environmental context to early hominins is as important as describing the hominin fossils themselves, because evolutionary processes are tightly linked to everchanging ecosystems that vary across space and

Providing an environmental context to early hominins is as important as describing the hominin fossils themselves, because evolutionary processes are tightly linked to everchanging ecosystems that vary across space and through time. An optimal understanding of ecosystems changes is critical to formulate and test hypotheses regarding human evolution and adaptation. Fortunately, the fossil record has yielded abundant remains of mammals which can be used to explore the possible causal relationships between environmental change and mammal – including hominin –evolution. Although many studies have already been conducted on this topic, most of them are framed at large spatial and temporal scales. Instead, this dissertation focuses on the evolution and paleoecology of only one group of mammals (the Suidae) in a specific geographical area (lower Awash Valley in Ethiopia) and within a constrained time frame (3.8–2.6 Ma). Three dissertation papers address: 1) changes in suid taxonomic composition in relation to Late Pliocene faunal turnover ~2.8 Ma in the Lee-Adoyta basin, Ledi-Geraru; 2) comparisons of suid diets from Hadar (~3.45–2.95 Ma) with respect to those of Kanapoi (~4.1 Ma, West Turkana, Kenya); 3) the dietary ecology of the suids from Woranso-Mille (~3.8–3.2 Ma). Results of these papers show that 1) after ~2.8 Ma there is a replacement of suid species that is coupled with low relative abundance of suids. This is compatible with more open and/or arid environments at this time; 2) suid dietary breadth was broader in Hadar than in Kanapoi, but this is mostly driven by the dietary niche space occupied by Kolpochoerus in Hadar, a suid genus absent from Kanapoi; 3) suid diets vary both temporally and geographically within the lower Awash Valley. Kolpochoerus incorporates more C4 resources (e.g., grasses) in its diet after ~3.5 Ma and in general, suids after ~3.5 Ma in Woranso-Mille had C4-enriched diets in comparison with those from nearby Hadar and Dikika. Presumably, the changes in suid communities (relative abundance and taxonomic composition) and dietary shifts observed in suids were triggered by climatic and habitat changes that also contributed to shape the behavioural and morphological evolution of early hominins.

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  • 2018

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The geologic history of central and eastern Ledi-Geraru, Afar, Ethiopia

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Sedimentary basins in the Afar Depression, Ethiopia archive the progression of continental breakup, record regional changes in east African climate and volcanism, and host what are arguably the most important

Sedimentary basins in the Afar Depression, Ethiopia archive the progression of continental breakup, record regional changes in east African climate and volcanism, and host what are arguably the most important fossiliferous strata for studying early human evolution and innovation. Significant changes in rift tectonics, climate, and faunal assemblages occur between 3-2.5 million years ago (Ma), but sediments spanning this time period are sparse. In this dissertation, I present the results of a geologic investigation targeting sediments between 3-2.5 Ma in the central and eastern Ledi Geraru (CLG and ELG) field areas in the lower Awash Valley, using a combination of geologic mapping, stratigraphy, and tephra chemistry and dating. At Gulfaytu in CLG, I mapped the northern-most outcrops of the hominin-bearing Hadar Formation (3.8-2.9 Ma), a 20 m-thick section of flat-lying lacustrine sediments containing 8 new tephras that directly overlie the widespread BKT-2 marker beds (2.95 Ma). Paleolake Hadar persisted after 2.95 Ma, and the presence and characteristics of the Busidima Formation (2.7-0.016 Ma) indicates Gulfaytu was affected by a reversal in depositional basin polarity. Combined with regional and geophysical data, I show the Hadar Formation underlying CLG is >300 m thick, supporting the hypothesis that it was the lower Awash Pliocene depocenter. At ELG, I mapped >300 m of sediments spanning 3.0-2.45 Ma. These sediments coarsen upward and show a progression from fluctuating lake conditions to fluvial landscapes and widespread soil development. This is consistent with the temporal change in depositional environments observed elsewhere in the lower Awash Valley, and suggests that these strata are correlative with the Hadar Formation. Furthermore, the strata and basalts at ELG are highly faulted, and overprinted by shifting extension directions attributed to the northern migration of the Afar triple junction. The presence of fossiliferous beds and stone tools makes ELG a high-priority target for anthropological and archaeological research. This study provides a new temporally-calibrated and high-resolution record of deposition, volcanism, and faulting patterns during a period of significant change in the Afar.

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Date Created
  • 2013

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The development of adult sex-typed social behavior in Lemur catta

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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

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.

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  • 2012

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The dietary competitive environment of the origination and early diversification of euprimates in North America

Description

The earliest Eocene marked the appearance of the first North American euprimates (adapids, omomyids). Despite the fact that leading hypotheses assert that traits involved in food acquisition underlie euprimate origination

The earliest Eocene marked the appearance of the first North American euprimates (adapids, omomyids). Despite the fact that leading hypotheses assert that traits involved in food acquisition underlie euprimate origination and early diversification, the precise role that dietary competition played in establishing euprimates as successful members of mammalian communities is unclear. This is because the degree of niche overlap between euprimates and all likely mammalian dietary competitors ("the euprimate competitive guild") is unknown. This research determined which of three major competition hypotheses - non-competition, strong competition, and weak competition - characterized the late Paleocene-early Eocene euprimate competitive guild. Each of these hypotheses is defined by a unique temporal pattern of niche overlap between euprimates and their non-euprimate competitors, allowing an evaluation of the nature of dietary competitive interactions surrounding the earliest euprimates in North America. Dietary niches were reconstructed for taxa within the fossil euprimate competitive guild using molar morphological measures determined to discriminate dietary regimes in two extant mammalian guilds. The degree of dietary niche separation among taxa was then evaluated across a series of fossil samples from the Bighorn Basin, Wyoming just prior to, during, and after euprimate origination. Statistical overlap between each pair of euprimate and non-euprimate dietary niches was determined using modified multivariate pairwise comparisons using distances in a multidimensional principal component "niche" space. Results indicate that euprimate origination and diversification in North America was generally characterized by the absence of dietary competition. This lack of competition with non-euprimates is consistent with an increase in the abundance and diversity of euprimates during the early Eocene, signifying that the "success" of euprimates may not be the result of direct biotic interactions between euprimates and other mammals. An examination of the euprimate dietary niche itself determined that adapids and omomyids occupied distinct niches and did not engage in dietary competition during the early Eocene. Furthermore, changes in euprimate dietary niche size over time parallel major climatic shifts. Reconstructing how both biotic and abiotic mechanisms affected Eocene euprimates has the potential to enhance our understanding of these influences on modern primate communities.

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  • 2014

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Variation in dental microwear textures and dietary variation in African Old World monkeys (Cercopithecidae)

Description

Dietary diversity is an important component of species’s ecology that often relates to species’s abundance and geographic distribution. Additionally, dietary diversity is involved in many hypotheses regarding the geographic distribution

Dietary diversity is an important component of species’s ecology that often relates to species’s abundance and geographic distribution. Additionally, dietary diversity is involved in many hypotheses regarding the geographic distribution and evolutionary fate of fossil primates. However, in taxa such as primates with relatively generalized morphology and diets, a method for approximating dietary diversity in fossil species is lacking.

One method that has shown promise in approximating dietary diversity is dental microwear analyses. Dental microwear variance has been used to infer dietary variation in fossil species, but a strong link between variation in microwear and variation in diet is lacking. This dissertation presents data testing the hypotheses that species with greater variation in dental microwear textures have greater annual, seasonal, or monthly dietary diversity.

Dental microwear texture scans were collected from Phase II facets of first and second molars from 309 museum specimens of eight species of extant African Old World monkeys (Cercopithecidae; n = 9 to 74) with differing dietary diversity. Dietary diversity was calculated based on food category consumption frequency at study sites of wild populations. Variation in the individual microwear variables complexity (Asfc) and scale of maximum complexity (Smc) distinguished groups that were consistent with differences in annual dietary diversity, but other variables did not distinguish such groups. The overall variance in microwear variables for each species in this sample was also significantly correlated with the species’s annual dietary diversity. However, the overall variance in microwear variables was more strongly correlated with annual frequencies of fruit and foliage consumption. Although some variation due to seasonal and geographic differences among individuals was present, this variation was small in comparison to the variation among species. Finally, no association was found between short-term monthly dietary variation and variation in microwear textures.

These results suggest that greater variation in microwear textures is correlated with greater annual dietary diversity in Cercopithecidae, but that variation may be more closely related to the frequencies of fruit and foliage in the diet.

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  • 2015

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Ecological role of dry-habitat chimpanzees (Pan troglodytes schweinfurthii) at Issa, Ugalla, Tanzania

Description

Identifying the ecological role, or niche, that a species occupies within their larger community elucidates environmental adaptability and evolutionary success. This dissertation investigates the occupied niche of chimpanzees (Pan troglodytes

Identifying the ecological role, or niche, that a species occupies within their larger community elucidates environmental adaptability and evolutionary success. This dissertation investigates the occupied niche of chimpanzees (Pan troglodytes schweinfurthii) living in an open, dry savanna-woodland environment by examining patterns of resource use and interspecific interactions. Data were collected October 2010--November 2011 at Issa, in the Ugalla region of western Tanzania, which is one of the driest, most open, and seasonal habitats inhabited by chimpanzees. Unlike most primatological studies which employ methods that include focal follows, this study focused instead on observing 'resource patches' for chimpanzees. Patch focals allow for the observation of all animals within a study area; capture resources that are not used by the study species; and are particularly well suited for unhabituated communities. In order to better understand relationships between environment and behavior, data collected at Issa are compared with published data from other chimpanzee populations. Issa chimpanzees were expected to have broader resource use than forest chimpanzees, as well as increased competition with other fauna, due to fewer available resources. However, in contrast to the assumption of food scarcity in dry habitats, dietary resources were available throughout the year. Like other populations, the diet of Issa chimpanzees consisted of mostly fruit, but unlike at other sites, the majority of plants consumed were woodland species. Additionally, although chimpanzees and other fauna shared spatial and dietary resources, there was only nominal overlap. These results point to extremely low levels of indirect competition between chimpanzees and other fauna. Despite extensive study of forest chimpanzees, little is known about their role within their faunal community in open, dry habitats, nor about how greater seasonality affects resource use. This project addresses both of these important issues and fosters novel approaches in anthropological studies, especially in reference to chimpanzee ecology and evolution. Understanding current chimpanzee behavioral relationships with their environments shapes hypotheses about their pasts, and also informs predictions about behaviors of similar taxa in paleo-environments. Lastly, examining the ecological role of chimpanzees within their larger communities will influence the formation of, as well as evaluate, conservation strategies.

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  • 2013

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Zooarchaeological and taphonomic analyses of Pleistocene vertebrate fauna from the Middle and Later Stone Age occupations at Contrebandiers Cave, Atlantic coast, Morocco

Description

This dissertation research describes the hunting behavior of early modern humans through the analysis of vertebrate faunal remains from Contrebandiers Cave, Morocco. Contrebandiers Cave is located in the town of

This dissertation research describes the hunting behavior of early modern humans through the analysis of vertebrate faunal remains from Contrebandiers Cave, Morocco. Contrebandiers Cave is located in the town of Témara and is roughly 250 meters from the current shoreline of the Atlantic Ocean. The cave was excavated in the 1950s and 1970s by l’Abbé Roche, and again starting in 2007 by Dibble and El Hajraoui with total station plotting of finds. Contrebandiers Cave contains Middle Stone Age (MSA) deposits dated to Marine Isotope Stages (MIS) 5e, 5d and 5c, ~120,000 to ~96,000 years ago. The Later Stone Age (LSA) deposits are dated to MIS 2, ~20,000 years ago. The entirety of the ~12,000 vertebrate faunal remains from Dibble and El Hajraoui’s excavation were analyzed for taxonomic and taphonomic identification.

A total of 67 vertebrate taxa were identified and include ungulates, carnivores, lagomorphs, birds, tortoises, snakes and fish. The faunal remains from Contrebandiers Cave preserve surface modification that indicates both humans and carnivores acted as agents of prey accumulation. Skeletal element representation and surface modification of ungulate remains suggest that humans had primary access to small, medium and large-bodied prey. In the MSA levels, carnivore skeletal remains preserve surface modification that is interpreted as being indicative of behavior associated with skinning for fur removal.

The vertebrate faunal remains from MIS 5e and 5d indicate that humans were hunting grazers and mixed feeders from open habitats and suids from mixed habitats. The faunal remains from MIS 5c indicate that humans focused less on suids and more on mixed feeders from open habitats. The vertebrate faunal remains from MIS 2 reveal humans hunting grazers from dry, open habitats. This research provides a description of human hunting behavior in North Africa, and contributes to our understanding of early modern human behavior prior to dispersal out of Africa.

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Date Created
  • 2018