abstract: Facial projection--i.e., the position of the upper face relative to the anterior cranial fossa--is an important component of craniofacial architecture in primates. Study of its variation is therefore important to understanding the bases of primate craniofacial form. Such research is relevant to studies of human evolution because the condition in Homo sapiens--in which facial projection is highly reduced, with the facial skeleton located primarily inferior (rather than anterior) to the braincase--is derived vis-à-vis other primates species, including others in the genus Homo. Previous research suggested that variation in facial projection is explained by: (1) cranial base angulation; (2) upper facial length; (3) anterior cranial base length; (4) anterior sphenoid length; and/or (5) anterior middle cranial fossa length. However, previous research was based on taxonomically narrow samples and relatively small sample sizes, and comparative data on facial projection in anthropoid primates, with which these observations could be contextualized, do not currently exist. This dissertation fills this gap in knowledge. Specifically, data corresponding to the hypotheses listed above were collected from radiographs from a sample of anthropoid primates (N = 37 species; 756 specimens) . These data were subjected to phylogenetically-controlled multiple regression analyses. In addition, multivariate and univariate models were statistically compared, and the position of Homo sapiens relative to univariate and multivariate regression models was evaluated. The results suggest that upper facial length, anterior cranial base length, and, to a lesser extent, cranial base angle are the most important predictors of facial projection. Homo sapiens conforms to the patterns found in anthropoid primates, suggesting that these same factors explain the condition in this species. However, a consideration of the evidence from the fossil record in the context of these findings suggests that upper facial length is the most likely cause of the extremely low degree of facial projection in Homo sapiens. These results downplay the role of the brain in shaping the form of the human cranium. Instead, these results suggest that reduction in facial skeleton size--which may be due to changes in diet--may be more important than previously suggested. / Doctoral Dissertation Anthropology 2014

Les plus anciens anthropoïdes fossiles sont issus de plusieurs formations géologiques asiatiques de l'Eocène moyen à tardif (47 à 34 millions d'années), parmi lesquelles la formation de Pondaung (Birmanie) a délivré la faune la plus diverse. L'objectif de cette thèse est de reconstituer la paléogéographie, l'environnement et le climat de l'Eocène birman afin de mieux comprendre leur histoire évolutive. Dans un premier temps, l'évolution de la provenance du sédiment de Birmanie centrale a été étudiée par une approche alliant pétrographie, lithostratigraphie et géochimie isotopique. L'étude montre que la Birmanie centrale est restée à l'écart de tout apport sédimentaire himalayen et tibétain et formait, à l'Eocène, une bande côtière connectant l'avant-pays indien avec la région de la Sonde. Les paléoenvironnements de la formation de Pondaung ont ensuite été reconstitués par une approche combinant sédimentologie fluviale, pédologie et paléobotanique. Ces approches révèlent un paysage de marécages saisonniers, de forêts ripariennes et d'espaces ouverts, développés sous un climat tropical à forte saisonnalité. Les bois fossiles identifiés représentent différents écotones forestiers similaires à ceux des forêts de mousson actuelles. L'étude en isotope stable de gastéropodes fossiles et de dents de mammifères confirme un régime de précipitation semblable à la mousson moderne. Les paléoenvironnements de Pondaung contrastent avec l'idée d'épaisses forêts primaires comme habitat préférentiel des premiers anthropoïdes et lient leur biodiversité aux zones tropicales saisonnières, où les plus grosses espèces, comme les amphipithécidés, étaient particulièrement compétitives. / The fossil record of the first anthropoids is currently fed by several Middle to Late Eocene Asian strata (47 to 34 millions years ago), of which the Pondaung Formation in Myanmar has yielded the most diverse and prolific fauna. The aim of this PhD is to reconstruct the paleogeography, paleoenvironments, and paleoclimate of the Eocene Burmese successions in order to better constrain the early evolutionary history of the anthropoids. The sediment provenance of central Myanmar was first studied using a multi-proxy approach, combining petrography, sedimentology and isotope geochemistry. Results show that central Myanmar was isolated from any Himalayan or Tibetan input and additionally formed a narrow coastal band linking the Indian foreland with the Sunda area during the Eocene. Alluvial palaeoenvironments of the Pondaung Formation were then reconstructed through a combined sedimentological, pedological and paleobotanical approach. Results revealed a mosaic landscape with seasonal swamps, riparian forests, and open areas, expanding under a tropical climate with significant seasonality. Fossil woods form different ecotones similar to those of modern days monsoonal forests. Paleoclimate reconstruction through stable isotope geochemistry on mammalian fossil teeth and fossil gastropods confirms a monsoonal, modern-like rainfall regime in the Eocene. Pondaung paleoenvironments contrast with the idea of Eocene evergreen rainforests as a preferential living environment for the first anthropoids and link the Eocene biodiversity of anthropoid fauna to the tropical seasonal areas, where the biggest species, such as the amphipithecids, were particularly competitive.