Browsing by Subject "Paleontology"
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Item Open Access A 3D Geometric Morphometric Investigation of Relatedness in the Modern Human, Chimpanzee, and Homo naledi Postcranial Skeleton(2023) Rossillo, Amanda NoelleStudies of skeletal variation form the basis of our understanding of our species’ history and diversity. This most commonly takes the form of comparative, between- species studies aimed at reconstructing phylogenetic relationships. However, studies of within-species variation can provide insights into relatedness at smaller scales, which can shed light on important microevolutionary processes and be used to identify closely related individuals in the absence of DNA. This dissertation assesses the relationship between genetic and skeletal variation within groups of related and unrelated Homo sapiens and Pan troglodytes, with the aim of better understanding the population sampled by the seemingly homogenous Homo naledi assemblage from the Dinaledi Chamber in Rising Star Cave, South Africa. The hypotheses tested were: 1) closely related individuals exhibit less skeletal variation compared to unrelated individuals, and 2) the Dinaledi assemblage exhibits less morphological variation than H. sapiens and P. troglodytes at the species level, more closely resembling a single population.
Skeletal variation within a subset of H. sapiens from the crypt of Christ Church in Spitalfields, London (17-19th centuries A.D) with documented genealogies and the Gombe population of P. t. schweinfurthii was compared to species-wide baselines and the H. naledi assemblage. The data consisted of 3D models of 556 postcranial elements (first metacarpal (Mc1), proximal femur, talus, calcaneus, and navicular) from 187 individuals that were generated from surface scanners or downloaded from MorphoSource.
This dissertation employed a relatively new 3D geometric morphometric workflow that captures the entire shape of an element through the use of an automated landmarking program and feature-aware registration process. Two hundred pseudolandmarks were automatically and optimally placed on each element. Following alignment, multiple univariate and multivariate statistical analyses were used to quantify shape variation within and between the three species, including distributions of Euclidean distances, Procrustes distances to the mean shapes, Principal Components Analyses (PCA), Between-Group PCA, and Discriminant Function Analyses. The coefficient of relationship was used to represent genetic distance between known genetic relatives within modern humans.
The results of the within-species analyses of skeletal variation support Hypothesis 1 in both modern humans and chimpanzees, though the signal of relatedness is differentially expressed within and across elements. In modern humans, the calcaneus can be used to distinguish known close relatives from distantly related and unrelated individuals. The navicular and femur were also found to be relatively good indicators of relatedness. Within chimpanzees, the talus is the most effective at distinguishing the Gombe population from the species-wide chimpanzee sample, followed by the calcaneus and femur. Within H. naledi, the talus varied the least while the navicular varied the most, though the high levels of variation found in the navicular and Mc1 are likely due to the state of preservation of these elements. The results of the interspecies analyses are more ambiguous. When considering the best preserved elements, the H. naledi talus varies the least within the three species, while the femur varies more than those of either H. sapiens or P. troglodytes at the species level. Hypothesis 2 is thus supported for the talus while rejected in the femur, suggesting that it cannot be rejected as a whole and that the patterns of homogeneity previously observed within H. naledi are more nuanced than previously recognized.
Item Open Access A baseline paleoecological study for the Santa Cruz Formation (late–early Miocene) at the Atlantic coast of Patagonia, Argentina(Palaeogeography, Palaeoclimatology, Palaeoecology, 2010-06) Vizcaíno, SF; Bargo, MS; Kay, RF; Fariña, RA; Di Giacomo, M; Perry, JMG; Prevosti, FJ; Toledo, N; Cassini, GH; Fernicola, JCCoastal exposures of the Santa Cruz Formation (late-early Miocene, southern Patagonia, Argentina) between the Coyle and Gallegos rivers have been a fertile ground for recovery of Miocene vertebrates for more than 100 years. The formation contains an exceptionally rich mammal fauna, which documents a vertebrate assemblage very different from any living community, even at the ordinal level. Intensive fieldwork performed since 2003 (nearly 1200 specimens have been collected, including marsupials, xenarthrans, notoungulates, litopterns astrapotheres, rodents, and primates) document this assertion. The goal of this study is to attempt to reconstruct the trophic structure of the Santacrucian mammalian community with precise stratigraphic control. Particularly, we evaluate the depauperate carnivoran paleoguild and identify new working hypotheses about this community. A database has been built from about 390 specimens from two localities: Campo Barranca (CB) and Puesto Estancia La Costa (PLC). All species have been classified as herbivore or carnivore, their body masses estimated, and the following parameters estimated: population density, on-crop biomass, metabolic rates, and the primary and secondary productivity. According to our results, this model predicts an imbalance in both CB and PLC faunas which can be seen by comparing the secondary productivity of the ecosystem and the energetic requirements of the carnivores in it. While in CB, the difference between carnivores and herbivores is six-fold, in PLC this difference is smaller, the secondary productivity is still around three times that of the carnivore to herbivore ratio seen today. If both localities are combined, the difference rises to around four-fold in favour of secondary productivity. Finally, several working hypotheses about the Santacrucian mammalian community and the main lineages of herbivores and carnivores are offered. © 2010 Elsevier B.V. All rights reserved.Item Open Access Body Mass Prediction from Dental and Postcranial Measurements in Primates and Their Nearest Relatives(2017) Yapuncich, Gabriel StephenTo evaluate alternative hypotheses for the role of mass and muscle-induced forces in joint construction, the allometric scaling relationships of the articular facets of the talus were estimated with phylogenetic regressions. Many articular surfaces scale with significant positive allometry, suggesting that mass-induced forces are an important influence for the bony architecture of synovial joints.
Using a large sample of primates and their nearest living relatives, body mass prediction equations were generated from the articular facet areas of the talus and calcaneus. Those facets that scaled with positive allometry were both accurate and precise. Compared to previously published prediction equations, the novel equations developed for this study were substantially more reliable.
Several methodological debates for body mass prediction were also evaluated. Prediction equations had their highest correlations when species with greater than a 20% difference between sexes are represented by both males and females. Using dental measurements from cercopithecoids housed at the National Museum of Natural History, predictive accuracy was maximized when body mass was predicted using a mean value estimated from a robust sample. Even when only a single individual was represented, tests of predictive accuracy using primates with associated body masses from several localities (Hacienda La Pacifica, Costa Rica; Gombe Stream National Park, Tanzania; Amboseli Reserve, Kenya; and the Duke Lemur Center) demonstrated that prediction equations provide more accurate predictions of species mean values than individual-specific values.
The importance of longitudinal change in body mass was evaluated by comparing coefficients of variation for individual and mean body mass of the populations at La Pacifica, Gombe, and the Duke Lemur Center. Individual coefficients of variation were significantly greater than the population coefficients of variation, which suggests that mean body masses are more stable “targets” of prediction.
Finally, the novel prediction equations were applied to a sample of sympatric primates with associated dental and postcranial elements from the middle Eocene of Wyoming, including Notharctus tenebrosus, Smilodectes gracilis, Omomys carteri, and Hemiacodon gracilis. New body mass predictions suggest two pairs of similarly sized primates: N. tenebrosus and S. gracilis (~2500g), and O. carteri and H. gracilis (~400g). Thus, niche partitioning between closely related taxa was probably achieved through differences in diets, rather than differences in body mass.
Item Open Access Dietary inference from upper and lower molar morphology in platyrrhine primates.(PLoS One, 2015) Allen, Kari L; Cooke, Siobhán B; Gonzales, Lauren A; Kay, Richard FThe correlation between diet and dental topography is of importance to paleontologists seeking to diagnose ecological adaptations in extinct taxa. Although the subject is well represented in the literature, few studies directly compare methods or evaluate dietary signals conveyed by both upper and lower molars. Here, we address this gap in our knowledge by comparing the efficacy of three measures of functional morphology for classifying an ecologically diverse sample of thirteen medium- to large-bodied platyrrhines by diet category (e.g., folivore, frugivore, hard object feeder). We used Shearing Quotient (SQ), an index derived from linear measurements of molar cutting edges and two indices of crown surface topography, Occlusal Relief (OR) and Relief Index (RFI). Using SQ, OR, and RFI, individuals were then classified by dietary category using Discriminate Function Analysis. Both upper and lower molar variables produce high classification rates in assigning individuals to diet categories, but lower molars are consistently more successful. SQs yield the highest classification rates. RFI and OR generally perform above chance. Upper molar RFI has a success rate below the level of chance. Adding molar length enhances the discriminatory power for all variables. We conclude that upper molar SQs are useful for dietary reconstruction, especially when combined with body size information. Additionally, we find that among our sample of platyrrhines, SQ remains the strongest predictor of diet, while RFI is less useful at signaling dietary differences in absence of body size information. The study demonstrates new ways for inferring the diets of extinct platyrrhine primates when both upper and lower molars are available, or, for taxa known only from upper molars. The techniques are useful in reconstructing diet in stem representatives of anthropoid clade, who share key aspects of molar morphology with extant platyrrhines.Item Open Access Endocranial volume and shape variation in early anthropoid evolution(2014) Allen, Kari LeighFossil taxa are crucial to studies of brain evolution, as they allow us to identify evolutionary trends in relative brain size and brain shape that may not otherwise be identifiable in comparative studies using only extant taxa, owing to multiple events of parallel encephalization among primate clades. This thesis combines indirect and direct approaches to understanding primate evolution, by evaluating variation in the endocranial morphology of extant primates and their fossil representatives. I use a comparative approach to examine the relationships between interspecific adult endocranial volume and shape, and brain evolution and cranial form among extant primate clades and their fossil representatives. The associations are evaluated via phylogenetically informed statistics perfomed on volumetric measurements and three-dimensional geometric morphometric analyses of virtual endocasts constructed from micro-CT scans of primate crania. Fossil taxa included in these analyses are: 1) anthropoids Parapithecus, Aegyptopithecus (Early Oligocene, Egypt), Homunculus and Tremacebus (Early Miocene, Argentina), and 2) Eocene euprimates Adapis and Leptadapis (Eocene adapoids, France), and the Rooneyia (Eocene omomyoid, Texas).
The first part of this work (Chapter 2) explores variation in residual mass of brain components (taken from the literature) among primates, and evaluates the correlated evolution of encephalization and brain proportions with endocast shape, quantified via three-dimensional geometric morphometric techniques. Analyses reveal a broad range of variation in endocast shape among primates. Endocast shape is influenced by a complex array of factors, including phylogeny, body size, encephalization, and brain proportions (residual mass of brain components). The analysis supports previous research, which concludes that anthropoids and tarsiers (Haplorhini) share the enlargement of several key brain regions including the neocortex and visual systems, and a reduction of the olfactory system. Anthropoids further differ from strepsirrhines in endocranial features associated with encephalization--a more flexed brain base, an inferiorly deflected olfactory fossa--and those associated with brain proportions--a small olfactory fossa, and a more caudally extended cerebrum that extends posteriorly past the cerebellar poles. Tarsiers are unique in having a mediolaterally broad and rostro-caudally short endocast with an attenuated anterior and middle cranial fossae. This morphology is likely related to the extreme orbital enlargement in this taxon, which limits anterior expansion of the endocranium. Finally, despite the correlation between residual endocranial volume and endocast shape among modern primates, early anthropoid fossils demonstrate a disconnect between these factors in sharing key features of endocast shape with extant anthropoids at a relatively small brain size.
The second part of this thesis (Chapter 3) explores the relationship between craniofacial organization--cranial base angle, facial size, facial hafting--and encephalization via the lens of the Spatial Constraints and Facial Packing Hypotheses. These hypotheses predict that interspecific adult variation in encephalization correlates with endocranial shape such that a larger brain for a given body size will be more "globular" or spherical in shape. These hypotheses futher predict that basicranial angle covaries with encephalization and that the relative size of the endocranium and facial skeleton will have an antagonistic effect on basicranial angle and facial hafting. Results show that various measures of globularity have inconsistent and weak relationships to phylogeny, encephalization, and basicranial flexion, owing to a diversity of clade-specific scaling patterns between the maximum length, breadth, and width of the endocast. Among extant primates, there is weak but significant evidence to suggest that both facial size and encephalization influence variation in basicranial flexion. Considering the fossil specimens in isolation, their relative ranks in encephalization, basicranial flexion, and midline facial size and shape follow the pattern expected from the Spatial and Facial Packing Hypotheses outlined above; however, relative to modern species, the early fossil anthropoids have more flexed cranial bases and shorter facial skeletons at much smaller level of encephalization than seen in modern anthropoids.
Together, the extant data suggest a moderately conserved pattern of correlated evolution among endocranial size, endocranial shape, brain proportions, and craniofacial organization, which may explain differences in endocranial and facial shape between extant strepsirrhine and anthropoid primates; however, the fossil record for early anthropoid evolution demonstrates that a shift towards key anthropoid-like traits of the endocranium, basicranium, and facial skeleton were initiated early in anthropoid evolution, with subsequent encephalization occurring within and among members of this clade. Thus, these anthropoid cranial traits evolved in tandem with changes in the relative size of brain components, rather than absolute or relative brain size alone. Basicranial flexion, facial length and orientation are influenced by both: 1) shifts in endocranial shape associated with changes in brain proportion--accounting for the initiation of the anthropoid-like craniofacial plan early in the evolution of the clade--and 2) encephalization, which influenced subsequent morphological divergence among extant anthropoid groups.
Item Open Access Intra and Interspecific Variation in Semicircular Canal Morphology in Primates and Implications for Locomotor Behavior Reconstruction Models(2015) Gonzales, Lauren AnnThe semicircular canals of the vestibular system detect angular head rotations and play a fundamental role in guiding motor reflexes during locomotor behaviors. While extensive research has documented the relationship between the semicircular canal shape (i.e. radius of curvature and canal length) and locomotor behaviors, levels of intraspecific variation in primates are relatively unknown. Predictive models using these metrics to reconstruct locomotion in extinct animals are generally based on one individual per species. Furthermore, the influence of body size and to a lesser degree brain size heavily influences overall canal morphology.
This study documents intraspecific variation in the size, shape and orientation of the semicircular canals in relation to changes in function, brain size, and body size via analysis of high resolution CT scans of large samples of extant primate species. I test the hypothesis that the extent of intraspecific variation differs across a sample of primates, reflecting the intensity of selective pressure on canal shape in species that require agility during locomotion. I also examine whether spatial constraints resulting from the size of the skull (reflected by the size of the brain) affect canal radii of curvature and canal orthogonality more strongly than observed agility during locomotion.
To this end, data was gathered from high-resolution CT images of museum specimens. For the comparative analysis, 14-matched pairs of adult extant primate species were selected that contrast in agility and brain size in closely related genera. CT images of these specimens were used to measure functional measures of canal sensitivity (e.g., canal radii of curvature, orthogonality). This data was used to test hypotheses concerning intraspecific and interspecific variation in semicircular canal functional morphology. This data was then combined with a larger mammalian dataset culled from the literature, to further test hypotheses relating to body-size and brain size dependent variation in individual canal metrics.
Evaluation of levels of intraspecific variation support the hypothesis put forth by Billet et al. (2012), that selection on canal morphology is relaxed in animals with slow locomotor behaviors, who are observed to have higher levels of intraspecific variation. Analyses of interspecific variation provides tentative support for the use of canal orthogonality in reconstructive models, most especially in canal angles that seem least effected by other constraints—brain size, etc. However, locomotor signals are complex and brain/skull interactions can potentially produce misleading results when reconstructing locomotor behaviors. This work highlights the importance of critically assessing comparative groups used for inferring behaviors in both extinct and extant animals.
Item Open Access Lemur Teeth in Three Keys: Dietary Adaptation, Ecospace Occupation, and Macroevolutionary Dynamics(2019) Fulwood, Ethan LucasDietary adaptation appears to have driven many aspects of the high-level diversification of primates. Dental topography metrics provide a means of quantifying morphological correlates of dietary adaptation and can be used to reconstruct dietary adaptation in extinct taxa, model ecospace occupation, and capture macroevolutionary trends across deep time. However, difficulties may arise in the interpretation of dental topography metrics from A) their sensitivity to digital mesh processing choices; B) their tendency to average morphological information across tooth surfaces; and C) potential mismatches between the material properties understood theoretically to drive tooth shape and the measured properties of categorically defined primate diets. The full potential of pairing dental topography metrics with modern phylogenetic comparative methods, which would allow the evolutionary history of diet in large clades to be explored statistically, has yet to be explored.
In this dissertation, I attempt to address issues in the application of dental topography metrics, and extend them to new questions, using strepsirrhine primates as a model. The effectiveness of a recently described dental topography metric, ariaDNE, which is robust to details of mesh processing, in describing dietary adaptation in lower second molars is assessed. It is found that it performs at least as well as metrics more sensitive to mesh processing decisions. ariaDNE is then applied to segmented regions of lower second molars in order to assess the effect of averaging together potentially adaptively distinct tooth structures. I found no evidence that the aggregation of tooth structures significantly impairs dietary classification. These studies employ explicit methods for measuring overfitting risk, which has not previously been emphasized in applications of dental topography metrics.
Tooth shape is believed to reflect differences in the underlying material properties of the foods consumed by mammals, but the categories used to classify taxa to diets have inconsistent relationships with these food material properties. I attempt to address this inconsistency by relating tooth shape to expected geographic gradients in food material properties, an approach known as ecometrics. Dry, seasonal environments are expected to be associated with dental topography metrics associated with processing tougher foods. I find that ariaDNE is highest in highly seasonal but wet environments, supporting a role for the seasonal exploitation of fallback foods and that the availability of new leaves during wet periods may be important in driving community tooth sharpness. Tooth complexity is primarily driven by a stepwise increase in rainforest environments.
Dental topography metrics are then applied to several questions concerning the evolutionary history of lemurs. They are used to reconstruct the diets of seven genera of recently extinct, giant, subfossil lemurs, and find many of them to have exploited fruits and hard objects. Ecometric models are also applied to the reconstruction of paleoclimate at the ~500 year-old subfossil cave site of Ankilitelo, which records the last appearance of many subfossil lemur taxa. Models reconstruct a moister climate for Ankilitelo at the time of the accumulation of its subfossil fauna, supporting a role for climate alteration in the extirpation of the giant lemurs.
Finally, Dental topography metrics are combined with phylogenetic comparative methods to model the dietary evolution of lemurs in the context of adaptive radiation theory. Dental topography metrics do not show an early burst in rates of change or a pattern of early partitioning of subclade disparity in lemurs. However, rates of transition toward folivory were highest during the Oligocene, an interval of possible forest expansion on the island and of the dispersal of non-chiromyiform lemurs to Madagascar. Reconstruction of the ancestral molar morphology of ancestral nodes of the lemur tree suggest that the diversification of large bodied lemurs may have been driven by a shift toward the exploitation of defended plant resources.
Item Open Access Mammalian faunas, ecological indices, and machine-learning regression for the purpose of paleoenvironment reconstruction in the Miocene of South America(Palaeogeography, Palaeoclimatology, Palaeoecology, 2019-03-15) Spradley, JP; Glazer, BJ; Kay, RF© 2019 Elsevier B.V. Reconstructing paleoenvironments has long been considered a vital component for understanding community structure of extinct organisms, as well as patterns that guide evolutionary pathways of species and higher-level taxa. Given the relative geographic and phylogenetic isolation of the South American continent throughout much of the Cenozoic, the South American fossil record presents a unique perspective of mammalian community evolution in the context of changing climates and environments. Here we focus on one line of evidence for paleoenvironment reconstruction: ecological diversity, i.e. the number and types of ecological niches filled within a given fauna. We propose a novel approach by utilizing ecological indices as predictors in two regressive modeling techniques—Random Forest (RF) and Gaussian Process Regression (GPR)—which are applied to 85 extant Central and South American localities to produce paleoecological prediction models. Faunal richness is quantified via ratios of ecologies within the mammalian communities, i.e. ecological indices, which serve as predictor variables in our models. Six climate/habitat variables were then predicted using these ecological indices: mean annual temperature (MAT), mean annual precipitation (MAP), temperature seasonality, precipitation seasonality, canopy height, and net primary productivity (NPP). Predictive accuracy of RF and GPR is markedly higher when compared to previously published methods. MAT, MAP, and temperature seasonality have the lowest predictive error. We use these models to reconstruct paleoclimatic variables in two well-sampled Miocene faunas from South America: fossiliferous layers (FL) 1–7, Santa Cruz Formation (Early Miocene), Santa Cruz Province, Argentina; and the Monkey Beds unit, Villavieja Formation (Middle Miocene) Huila, Colombia. Results suggest general concordance with published estimations of precipitation and temperature, and add information with regards to the other climate/habitat variables included here. Ultimately, we believe that RF and GPR in conjunction with ecological indices have the potential to contribute to paleoenvironment reconstruction.Item Open Access Ontogeny of Lower Limb Morphology and Proportions in the Dinaledi Hominins(2015) Walker, Christopher ScottThe discovery of hundreds of fossil hominin remains from the Dinaledi Chamber of Rising Star cave in South Africa included dozens of immature elements attributed to multiple individuals. Some of these elements are amongst the most complete in the Dinaledi assemblage, but have not yet been fully studied. Thorough examination of these immature remains is important because they can provide a more complete understanding of the morphology of the Dinaledi hominins, facilitate an assessment of morphological development in the assemblage, and allow for direct comparisons with other immature fossil hominins. This dissertation focuses on the most diagnostic specimens of the immature lower limb (with reference to the immature upper limb and the mature sample) from the site and utilizes a comparative approach examining developmental variation in the proximal femur and limb proportions of extinct and extant ape species to discern the ontogenetic basis of the adult Dinaledi hominin form.
The first portion of this dissertation addresses the development of proximal femoral shape in an ontogenetic series of femora from the Dinaledi hominins, modern humans, chimpanzees, and gorillas. Results indicate that the development of proximal diaphyseal shape and neck-shaft angle are conserved within Homininae, but that neck shape may develop differently in bipeds than non-bipeds. The absolute shape of the femoral neck, however, markedly differs between the Dinaledi sample and modern humans, with greater anteroposterior constriction of the neck in the former, potentially due to increased superioinferior loading of the region associated with differing locomotor kinematics between species.
The second portion of this dissertation investigates the relative proportions of the immature Dinaledi lower limb. To date, the only lower limb long bone preserving the entire diaphysis and an articular surface to be recovered from the chamber, is the immature tibia, U.W. 101-1070. The length of this specimen was evaluated relative to the size of the preserved joint surface in an ontogenetic context and was found to be relatively long compared to other fossil hominins and even modern humans. The humero-tibial proportions of the immature Dinaledi hominins were found to be outside of the range of chimpanzees and gorillas, but comparable to modern humans and the immature Homo erectus specimen KNM-ER 15000. Together, these findings demonstrate that, with respect to relative lower limb length, the Dinaledi hominins are highly derived.
The mixture of primitive (australopith-like) and derived (Homo-like) features of the Dinaledi hominins identified in this dissertation are consistent with other early work on the assemblage and imply that the Dinaledi chamber contains Plio-Pleistocene hominins. Given small brain and predicted body sizes for the Dinaledi hominins, the results presented here suggest that relative limb elongation may have occurred prior to increases in brain and body size during hominin evolution and that bipedal energetic efficiency may have been the primary locus of selection.
Item Open Access The Anatomy of Mastication in Extant Strepsirrhines and Eocene Adapines(2008-04-25) Perry, Jonathan Marcus GlenThe jaw adductor muscles in strepsirrhines were dissected and their fiber architecture was quantified. Bite force and leverage were estimated using values for physiological cross-sectional area (PCSA) of the jaw adductors and lateral photographs of skulls. Jaw adductor mass, PCSA, fiber length, and bite force scale isometrically to body size. An experiment carried out at the Duke Lemur Center demonstrated that ingested food size also scales isometrically to body size. Folivorous strepsirrhines are characterized by short jaw adductor fibers, uniformly small ingested food size, large masseter and medial pterygoid muscles (in PCSA and mass), and large estimated bite force for their jaw length. Large-bodied folivores have especially large jaw adductors. Small-bodied folivores have especially short jaws, but do not have especially large jaw adductors. Folivores probably can generate large bite forces; they possess short jaws (short bite load arms) and/or large jaw adductor cross-sectional areas. Frugivorous strepsirrhines are characterized by long jaws, large (but variable) ingested food size, large temporalis muscles, and small estimated bite force for their jaw length. Frugivores have long jaw adductor fibers that likely maintain tension during the ingestion of large objects (e.g., fruits). The temporalis is large in frugivores, not because it has superior leverage during incision, but because its fibers likely do not stretch as much at wide gapes as those of the other adductors. Correlations between osteological landmarks and jaw adductor dimensions in strepsirrhines were used to infer jaw adductor dimensions in Adapis parisiensis and Leptadapis magnus (Adapinae) from the Eocene of Europe. Inferred PCSA and lateral photographs were used to estimate bite force and leverage in these adapines. An analysis of shearing quotients was also performed. Inferred jaw adductor mass, PCSA, bite force, and shearing quotients are great in adapines relative to extant strepsirrhines. All anatomical signals suggest a diet rich in tough leaves and other structural plant parts, perhaps with some small fruits. Adapis was likely more folivorous than Leptadapis.Item Open Access The Cenozoic History of the Andean Foreland in Southeastern Peru(2018) Salenbien, WoutResults from two geographical study areas are presented in this dissertation, contributing important new information about the Cenozoic geological, environmental and biological regime. At the first locality along the Manu River (11.90°S, 71.34°W) I present a revised age and reinterpret the depositional environment. Age determination consisted of radiometrically dating detrital zircons, pushing the technical boundaries of this technique, paired with radiocarbon analyses of depositional organic material. Constraining the depositional environment relied on geochemical and sedimentological analyses. The revised age, 0.13±0.04 Ma instead of ~9 Ma, and depositional environment, as a fluvial overbank deposit instead of estuarine or marginal-marine deltaic deposits, have major implications for research previously published on the outcrop.
A second section is realized along the Alto Madre de Dios river and is situated in a piggyback basin belonging to the frontmost active deformation zone of the Sub Andean Zone, located approximately 12.8°S and 71.3°W. The section spans from the Paleocene to the Quaternary in time and allows a constraint on the influence of the Andean orogeny on the Madre de Dios foreland basin and the fauna and flora it contained through the Cenozoic. Field work has yielded a series of fossil localities that have been constrained in age through use of U/Pb dating of detrital zircons. Notable fossil finds include Early Miocene marsupials, xenarthrans, rodents, notoungulates, and bats. A new primate recovered from the section is the first record of a primate from the Early Miocene of the Amazon Basin. Reconstruction of the depositional environment for each formation was performed by a combined use of sedimentology, geochemistry, and paleontology. Stable isotopic analyses on depositional organic material indicates continental depositional settings for all formations, whereas stable isotopic analyses on abiogenic carbonates provide constraints on the degree of diagenetic alteration of sediments varying with age and structural setting. Sedimentary facies are consistent with deposits being formed in fluvial and overbank environments, consisting of fine-grained floodplain deposits, point bar deposits, conglomerate channels and fossil-bearing channel lag deposits. Average grain size for the section shows a coarsening trend towards younger deposits, consistent with the approach of, and incorporation into an active orogen, as supported by provenance data from detrital zircon analyses.
Item Open Access The Functional Significance of Early Homo Pelvis Morphology(2024) Cook, Rebecca WThe transition from the Pliocene to the Pleistocene appears to be a time of major transition in the hominin lineage with likely adaptive shifts in behavior. Homo erectus is a temporally broad species with apparent behavioral plasticity and potentially related morphological variability. Some H. erectus postcranial material exhibits traits that indicate a general trend of mechanical reinforcement at loadbearing sites across the pelvis and femur. One such fossil, KNM-ER 3228, is a presumed H. erectus os coxae that is representative of this morphological pattern of robusticity, which includes pronounced acetabulosacral and acetabulocristal buttresses and rugose musculoligamentous attachment sites. This femoropelvic complex represents an evolutionarily stable morphological pattern across a significant portion of the Pleistocene, but its biomechanical significance is not well understood. Moderate increases in encephalization combined with an increase in body size seen in H. erectus may be implicated in early Homo pelvic evolution, as the mechanical consequences of a larger body and expansion of the birth canal for parturition may have led to increased loads during locomotion. The retention of ancestral traits in the H. erectus pelvis (such as laterally flared ilia), coupled with derived traits (such as the expanded birth canal), may have necessitated greater robusticity in the pelvis to reduce strain magnitudes in the bone. Alternatively, this robusticity may be serving to reduce strains within the context of behavioral adaptations, such as endurance running or long-distance walking, that may have increased the magnitude or frequency of loads relative to australopiths. This dissertation addresses two objectives relative to the biomechanical significance of the femoropelvic complex of H. erectus. Objective 1 is to investigate the degree to which the patterns we see in some H. erectus pelves are due to body size scaling of bony features resulting from an evolutionary increase in body size. Objective 2 is to determine what, if any, functional significance may be assigned to the femoropelvic complex, beyond that which body size scaling to keep strain magnitudes within physiological limits may explain. A gait analysis study is conducted in which kinematic and kinetic data from modern humans are collected and used as input for a series of finite element models. These models are created from a sample of modern humans, an Australopithecus africanus pelvis (Sts 14), and a novel reconstruction of KNM-ER 3228 (early Homo) created using 3D geometric morphometrics. The results of these finite element models lead to the rejection of the hypothesis that higher magnitude loads in the H. erectus pelvis resulting from increased body size and modest encephalization resulted in the increased robusticity of pelvic features. This mechanical robusticity was hypothesized to maintain strain levels within manageable physiological levels in the context of the retention of ancestral states. Instead, the lower strains incurred during normal bipedal walking in the H. erectus pelvis suggest a pelvis adapted to bipedal walking, beyond that which strain maintenance can explain. Further, the results of finite element analyses of KNM-ER 3228 and modern humans while running provide evidence to support a hypothesis that mechanical buttressing of the H. erectus pelvis is an adaptation to an increased number of loading cycles (relative to australopiths) in the context of long-distance walking and/or endurance running, and/or high magnitude loads in the context of endurance running. This dissertation contributes to the investigation of unanswered questions in Homo pelvic evolution and highlights the value of comparative modeling in paleoanthropology.
Item Open Access Tooth Root Size, Chewing Muscle Leverage, and the Biology of Homunculus patagonicus (Primates) from the Late Early Miocene of Patagonia(Ameghiniana, 2010-09) Perry, JMG; Kay, RF; Vizcaíno, SF; Bargo, MSInferences about the diet of Miocene platyrrhine monkeys have relied upon the morphology of the molar teeth, specifically the crests on the molars. Using a library of Micro-CT images of a broad comparative sample of living platyrrhines (callitrichines, cebines, pitheciids and atelids), late early Miocene Homunculus, and the early Miocene Tremacebus and Dolichocebus, we extend these inferences by examining the surface areas of the tooth roots, anchor points for the periodontal ligaments. From muscle scars on the skull, we estimate the mechanical leverage of the chewing muscles at bite points from the canine to the last molar. Extant platyrrhines that gouge bark to obtain exudates do not have especially large canine roots or anterior premolar roots compared with their less specialized close relatives. Extant platyrrhines that have more folivorous diets have much larger molar roots than do similar-sized more frugivorous species. Homunculus patagonicus has large postcanine roots relative to body size and poor masticatory leverage compared to the extant platyrrhines in our sample. The large postcanine roots, heavy tooth wear, and moderately-long shearing crests suggests a diet of abrasive, resistant foods. However, relatively poor jaw adductor leverage would have put the masticatory apparatus of Homunculus at a mechanical disadvantage for producing high bite forces compared to the condition in extant platyrrhines. Tremacebus and Dolichocebus, like Homunculus, have larger tooth root surfaces than comparable-sized living platyrrhines. They also resemble Homunculus in being more prognathic and having posteriorly-located temporalis origins - all features of a relatively poor leverage system. ©Asociación Paleontológica Argentina.