The oldest primates of modern aspect (euprimates) appear abruptly on the Holarctic continents dur... more The oldest primates of modern aspect (euprimates) appear abruptly on the Holarctic continents during a brief episode of global warming known as the Paleocene-Eocene Thermal Maximum, at the beginning of the Eocene (~56 Ma). When they first appear in the fossil record, they are already divided into two distinct clades, Adapoidea (basal members of Strepsirrhini, which includes extant lemurs, lorises, and bushbabies) and Omomyidae (basal Haplorhini, which comprises living tarsiers, monkeys, and apes). Both groups have recently been discovered in the early Eocene Cambay Shale Formation of Vastan lignite mine, Gujarat, India, where they are known mainly from teeth and jaws. The Vastan fossils are dated at ~54.5 Myr based on associated dinoflagellates and isotope stratigraphy. Here, we describe new, exquisitely preserved limb bones of these Indian primates that reveal more primitive postcranial characteristics than have been previously documented for either clade, and differences between them are so minor that in many cases we cannot be certain to which group they belong. Nevertheless, the small distinctions observed in some elements foreshadow postcranial traits that distinguish the groups by the middle Eocene, suggesting that the Vastan primatesdthough slightly younger than the oldest known euprimatesdmay represent the most primitive known remnants of the divergence between the two great primate clades.
Primates constituted a dominant part of the mammalian faunas of North America during the early an... more Primates constituted a dominant part of the mammalian faunas of North America during the early and middle parts of the Eocene (55-46 ma). Beginning in the Uintan North American Land Mammal Age (46-42 ma) primates declined in diversity and abundance in the Rocky Mountain region. This decline has been linked to the recession of tropical rain forests out of northern latitudes at that time. Climatic change of this magnitude would presumably have an impact on the contemporary mammalian faunas, with reduction or extinction of forest groups like primates, but perhaps radiation of mammals that preferred more open habitats such as artiodactyls. In this dissertation I describe and analyze the postcranial morphology of Uintan mammals from the Uinta Formation in Utah to address which lineages evolved to take advantage of arid habitats and which did not. The primary goal of this dissertation is to examine the relationship between mammalian postcranial functional adaptations and habitat change in...
Ecomorphology aims to link morphology with functional role within an ecological context. The arti... more Ecomorphology aims to link morphology with functional role within an ecological context. The artiodactyl astragalus is a common target of ecomorphological study due to its frequent preservation in the fossil record. Functional hypotheses predict that the tibial trochlea of the astragalus of highly cursorial taxa in open habitats should have steeply sloping surfaces to prevent joint dislocation during rapid locomotion. The need for lateral joint stability is relaxed in taxa that rely instead on crypsis to avoid predators in more closed habitats. However, previous attempts to analyze the tibial trochlea using linear measurements have yielded mixed results. We analyzed laser scans of 15 bovid (11 species) and three cervid astragali (two species). Models were oriented consistently, and the area corresponding to the tibial trochlea was extracted. A Digital Elevation Model raster was created and used to calculate the slope of each pixel on the surface. Values of the resulting slope raster...
American journal of physical anthropology, Jan 14, 2015
Comprehensive quantification of the shape and proportions of the medial tibial facet (MTF) of the... more Comprehensive quantification of the shape and proportions of the medial tibial facet (MTF) of the talus (=astragalus) has been lacking for Primates and their closest relatives. In this study, aspects of MTF form were quantified and employed to test hypotheses about their functional and phylogenetic significance. The following hypotheses influence perceptions of primate evolutionary history but are due for more rigorous assessment: 1) A relatively large MTF distinguishes "prosimians" (strepsirrhines and tarsiers) from anthropoids and non-primate euarchontans; 2) the distinctive form of the "prosimian" MTF is a correlate of locomotor tendencies that emphasize use of vertical and small diameter supports in conjunction with inverted, abducted foot postures; and 3) the "prosimian" MTF form arose along the primate stem lineage and was present in the euprimate common ancestor. Three-dimensional (3D) scanning was used to create scale digital models of tali (n =...
The oldest primates of modern aspect (euprimates) appear abruptly on the Holarctic continents dur... more The oldest primates of modern aspect (euprimates) appear abruptly on the Holarctic continents during a brief episode of global warming known as the Paleocene-Eocene Thermal Maximum, at the beginning of the Eocene (~56 Ma). When they first appear in the fossil record, they are already divided into two distinct clades, Adapoidea (basal members of Strepsirrhini, which includes extant lemurs, lorises, and bushbabies) and Omomyidae (basal Haplorhini, which comprises living tarsiers, monkeys, and apes). Both groups have recently been discovered in the early Eocene Cambay Shale Formation of Vastan lignite mine, Gujarat, India, where they are known mainly from teeth and jaws. The Vastan fossils are dated at ~54.5 Myr based on associated dinoflagellates and isotope stratigraphy. Here, we describe new, exquisitely preserved limb bones of these Indian primates that reveal more primitive postcranial characteristics than have been previously documented for either clade, and differences between them are so minor that in many cases we cannot be certain to which group they belong. Nevertheless, the small distinctions observed in some elements foreshadow postcranial traits that distinguish the groups by the middle Eocene, suggesting that the Vastan primatesdthough slightly younger than the oldest known euprimatesdmay represent the most primitive known remnants of the divergence between the two great primate clades.
Primates constituted a dominant part of the mammalian faunas of North America during the early an... more Primates constituted a dominant part of the mammalian faunas of North America during the early and middle parts of the Eocene (55-46 ma). Beginning in the Uintan North American Land Mammal Age (46-42 ma) primates declined in diversity and abundance in the Rocky Mountain region. This decline has been linked to the recession of tropical rain forests out of northern latitudes at that time. Climatic change of this magnitude would presumably have an impact on the contemporary mammalian faunas, with reduction or extinction of forest groups like primates, but perhaps radiation of mammals that preferred more open habitats such as artiodactyls. In this dissertation I describe and analyze the postcranial morphology of Uintan mammals from the Uinta Formation in Utah to address which lineages evolved to take advantage of arid habitats and which did not. The primary goal of this dissertation is to examine the relationship between mammalian postcranial functional adaptations and habitat change in...
Ecomorphology aims to link morphology with functional role within an ecological context. The arti... more Ecomorphology aims to link morphology with functional role within an ecological context. The artiodactyl astragalus is a common target of ecomorphological study due to its frequent preservation in the fossil record. Functional hypotheses predict that the tibial trochlea of the astragalus of highly cursorial taxa in open habitats should have steeply sloping surfaces to prevent joint dislocation during rapid locomotion. The need for lateral joint stability is relaxed in taxa that rely instead on crypsis to avoid predators in more closed habitats. However, previous attempts to analyze the tibial trochlea using linear measurements have yielded mixed results. We analyzed laser scans of 15 bovid (11 species) and three cervid astragali (two species). Models were oriented consistently, and the area corresponding to the tibial trochlea was extracted. A Digital Elevation Model raster was created and used to calculate the slope of each pixel on the surface. Values of the resulting slope raster...
American journal of physical anthropology, Jan 14, 2015
Comprehensive quantification of the shape and proportions of the medial tibial facet (MTF) of the... more Comprehensive quantification of the shape and proportions of the medial tibial facet (MTF) of the talus (=astragalus) has been lacking for Primates and their closest relatives. In this study, aspects of MTF form were quantified and employed to test hypotheses about their functional and phylogenetic significance. The following hypotheses influence perceptions of primate evolutionary history but are due for more rigorous assessment: 1) A relatively large MTF distinguishes "prosimians" (strepsirrhines and tarsiers) from anthropoids and non-primate euarchontans; 2) the distinctive form of the "prosimian" MTF is a correlate of locomotor tendencies that emphasize use of vertical and small diameter supports in conjunction with inverted, abducted foot postures; and 3) the "prosimian" MTF form arose along the primate stem lineage and was present in the euprimate common ancestor. Three-dimensional (3D) scanning was used to create scale digital models of tali (n =...
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