Papers by Marian Hamilton
Royal Society Open Science, 2021
Strontium isotope ratios (87 Sr/ 86 Sr) allow researchers to track changes in mobility throughout... more Strontium isotope ratios (87 Sr/ 86 Sr) allow researchers to track changes in mobility throughout an animal's life and could theoretically be used to reconstruct sex-biases in philopatry and dispersal patterns in primates. Dispersal patterns are a life-history variable that correlate with numerous aspects of behaviour and socio-ecology that are elusive in the fossil record. The present study demonstrates that the standard archaeological method used to differentiate between 'local' and 'non-local' individuals, which involves comparing faunal isotopic ratios with environmental isotopic minima and maxima, is not always reliable; aspects of primate behaviour, local environments, geologic heterogeneity and the availability of detailed geologic maps may compromise its utility in certain situations. This study instead introduces a different methodological approach: calculating offset values to compare
American Journal of Physical Anthropology, 2019
Objectives
Riparian or gallery forests are critical habitats for numerous plants and animals to... more Objectives
Riparian or gallery forests are critical habitats for numerous plants and animals today. Paleoanthropologically, reliance on such habitats informs behavioral and ecological reconstructions; for example, gallery forest habitats likely played a critical role in the transition from ape to hominin in the early Pliocene and may represent a preferred habitat for the last common ancestor of chimpanzees and humans. Direct indicators for gallery forest habitats preference are lacking. The objective of this article is to assess whether strontium isotope ratios are a reliable indicator of habitat preference for fauna living in and around gallery forests.
Materials and methods
We report bioavailable strontium isotope ratios from the Mugiri River, its tributaries, and its gallery forest (Toro-Semliki Wildlife Reserve, southwestern Uganda), and compare them to surrounding savanna-grassland values. We compare these environmental values to strontium isotopes ratios in faunal tooth enamel to determine if habitat preferences are accurately reflected.
Results
Gallery forest and savanna-grassland vegetations have significantly different strontium isotope ratio profiles. We trace these isotopic differences to the influence of the Mugiri tributaries, which originate on Paleoproterozoic gneiss deposits on top of the surrounding escarpments. These isotopic differences in vegetation are mirrored in the tissues of fauna with habitat preferences for either the gallery forest or the surrounding grasslands.
Discussion
This research demonstrates the potential of strontium isotope ratios to identify habitat preferences in modern or fossil fauna under proper geologic variability. It provides a methodological model for future studies seeking to reconstruct habitat preferences in early hominins.
Journal of Human Evolution, 2024
Dispersal patterns in primates have major implications for behavior and sociality but are difficu... more Dispersal patterns in primates have major implications for behavior and sociality but are difficult to reconstruct for fossil species. This study applies novel strontium isotope methodologies that have reliably predicted philopatry and dispersal patterns in chimpanzees and other modern primates to previously published strontium isotope ratios (87 Sr/ 86 Sr) of two South African hominins, Australopithecus africanus and Australopithecus robustus. In this study, the difference or 'offset' was calculated between the 87 Sr/ 86 Sr of each fossil tooth compared to local bioavailable 87 Sr/ 86 Sr as defined by cluster analysis of modern plant isotope ratios. Large teeth (presumably belonging to males) have low offsets from local 87 Sr/ 86 Sr proxies, while small teeth (presumably from females) have greater offsets from local 87 Sr/ 86 Sr proxies. This supports previous conclusions of male philopatry and female dispersal in both A. africanus and A. robustus. Furthermore, A. robustus shows more extreme differences between presumed males and females compared to A. africanus. This is analogous to differences seen in modern olive baboons compared to chimpanzees and suggests that A. africanus may have had a larger home range than A. robustus. Neither hominin species has 87 Sr/ 86 Sr consistent with riparian habitat preferences despite the demonstrated presence of riparian habitats in South Africa at the time.
Modern datasets provide the context necessary for accurate interpretations of isotopic data from ... more Modern datasets provide the context necessary for accurate interpretations of isotopic data from archaeological faunal assemblages. In this study, we use the oxygen isotope ratios (δ 18 O) of modern small mammals from Chaco Canyon, New Mexico, to quantify expected isotopic variation in a local population. The δ 18 O values of local, modern small mammals encompass a broad range (−6.0‰ to 4.8‰ VPDB), which is expected given the extreme seasonal variation in the δ 18 O of precipitation on the Colorado Plateau (−11‰ to −3‰ VPDB). Isotopic ratios of small mammals obtained from excavated archaeological sites in Chaco Canyon (ca. AD 800 to 1200) show no significant differences with their modern counterparts, suggesting that there is no difference in the origins of the archaeological small-mammal collection and the modern, local Chaco Canyon small-mammal collection. In contrast, δ 18 O values of large mammals from Chaco archaeological sites are significantly different from those of modern specimens, reflecting a nonlocal, but also nonspecific, source in the past. Los datos isotópicos de los animales modernos pueden proporcionar información importante para la interpretación de los datos isotópicos procedentes de conjuntos faunísticos arqueológicos. En este estudio utilizamos las proporciones de isótopos de oxígeno (δ 18 O) de pequeños mamíferos modernos en Chaco Canyon, Nuevo México, para cuantificar la variación esperada para una única población local. El rango de valores de δ 18 O de los pequeños mamíferos locales en Chaco Canyon es amplio (-6,0‰ a 4,8‰ VPDB). Esto no es sorprendente, dada la considerable variación estacional de δ 18 O ligada a la precipitación en la meseta del Río Colorado (-11‰ a-3‰ VPDB). Las proporciones isotópicas de los pequeños mamíferos arqueológicos procedentes de los sitios excavados en Chaco Canyon (ca. 800–1200 dC) no difieren de manera significativa de las de los animales modernos. Esto sugiere que no hay diferencias de procedencia entre la colección arqueológica de pequeños mamíferos y los mamíferos locales modernos de Chaco Canyon. En cambio, los valores de δ 18 O de los mamíferos grandes de los sitios arqueológicos de la zona son muy distintos de los valores de mamíferos grandes modernos. Esto sugiere que los especímenes de mamíferos grandes arqueológicos tienen origen diferente y no local, aunque no especulamos sobre dónde pudo haber sido ese lugar.
PLoS One, May 22, 2014
Strontium isotope sourcing has become a common and useful method for assigning sources to archaeo... more Strontium isotope sourcing has become a common and useful method for assigning sources to archaeological artifacts. In Chaco Canyon, an Ancestral Pueblo regional center in New Mexico, previous studies using these methods have suggested that significant portion of maize and wood originate in the Chuska Mountains region, 75 km to the West. In the present manuscript, these results were tested using both frequentist methods (to determine if geochemical sources can truly be differentiated) and Bayesian methods (to address uncertainty in geochemical source attribution). It was found that Chaco Canyon and the Chuska Mountain region are not easily distinguishable based on radiogenic strontium isotope values. The strontium profiles of many geochemical sources in the region overlap, making it difficult to definitively identify any one particular geochemical source for the canyon's pre-historic maize. Bayesian mixing models support the argument that some spruce and fir wood originated in the San Mateo Mountains, but that this cannot explain all 87Sr/86Sr values in Chaco timber. Overall radiogenic strontium isotope data do not clearly identify a single major geochemical source for maize, ponderosa, and most spruce/fir timber. As such, the degree to which Chaco Canyon relied upon outside support for both food and construction material is still ambiguous.
Conference Presentations by Marian Hamilton
Sr/Ca Ratios Measured via Nondestructive XRF Differentiate Frugivory and Folivory in Early North American Primates , 2024
Assessing contributions of frugivory and folivory to primate diets is critical across the evoluti... more Assessing contributions of frugivory and folivory to primate diets is critical across the evolutionary history of the primate clade. The rise of euprimates was almost certainly related to arboreality, but the debate over the relative importance of visual predation (insectivory) or coevolution with fruiting angiosperms continues. Dietary reconstructions of late-Paleocene, early-Eocene euprimates is highly variable and based primarily on morphology. Such adaptive proxies for diet are often confounded by phylogenetic issues, and non-adaptive reconstruction methods would be an important contribution to the paleontological toolkit. Studies in extant primates show frugivores have lower Sr/Ca ratios than folivores. It is unclear if such methods are transferable to samples spread across time and space. This pilot study presents trace element data gathered via non-destructive XRF measurements on early euprimates and plesiadapaformes from the collections at the University of Wyoming’s Geology Museum including the genera Microsyops, Cantius, Smilodectes, Notharctus, Teilhardina, and Tetonius. Initial results show elevated Sr/Ca ratios in the likely-folivorous Smilodectes and Notharctus specimens compared to the likely-frugivorous Cantius specimens. However, Sr/Ca ratios of Cantius are not as low as the frugivorous Hyracotherium, and the likely-frugivorous Microsyops has ratios more similar to folivores than frugivores. Omnivorous Teilhardina and Tetonius have the most elevated Sr/Ca ratios, which could be consistent with insectivory, although modern analogous datasets are currently lacking. These findings are encouraging for future use of Sr/Ca ratios as a means of reconstructing diet even in complex datasets. Larger comparative modern samples and greater fossil samples sizes are necessary to resolve lingering questions.
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Papers by Marian Hamilton
Riparian or gallery forests are critical habitats for numerous plants and animals today. Paleoanthropologically, reliance on such habitats informs behavioral and ecological reconstructions; for example, gallery forest habitats likely played a critical role in the transition from ape to hominin in the early Pliocene and may represent a preferred habitat for the last common ancestor of chimpanzees and humans. Direct indicators for gallery forest habitats preference are lacking. The objective of this article is to assess whether strontium isotope ratios are a reliable indicator of habitat preference for fauna living in and around gallery forests.
Materials and methods
We report bioavailable strontium isotope ratios from the Mugiri River, its tributaries, and its gallery forest (Toro-Semliki Wildlife Reserve, southwestern Uganda), and compare them to surrounding savanna-grassland values. We compare these environmental values to strontium isotopes ratios in faunal tooth enamel to determine if habitat preferences are accurately reflected.
Results
Gallery forest and savanna-grassland vegetations have significantly different strontium isotope ratio profiles. We trace these isotopic differences to the influence of the Mugiri tributaries, which originate on Paleoproterozoic gneiss deposits on top of the surrounding escarpments. These isotopic differences in vegetation are mirrored in the tissues of fauna with habitat preferences for either the gallery forest or the surrounding grasslands.
Discussion
This research demonstrates the potential of strontium isotope ratios to identify habitat preferences in modern or fossil fauna under proper geologic variability. It provides a methodological model for future studies seeking to reconstruct habitat preferences in early hominins.
Conference Presentations by Marian Hamilton
Riparian or gallery forests are critical habitats for numerous plants and animals today. Paleoanthropologically, reliance on such habitats informs behavioral and ecological reconstructions; for example, gallery forest habitats likely played a critical role in the transition from ape to hominin in the early Pliocene and may represent a preferred habitat for the last common ancestor of chimpanzees and humans. Direct indicators for gallery forest habitats preference are lacking. The objective of this article is to assess whether strontium isotope ratios are a reliable indicator of habitat preference for fauna living in and around gallery forests.
Materials and methods
We report bioavailable strontium isotope ratios from the Mugiri River, its tributaries, and its gallery forest (Toro-Semliki Wildlife Reserve, southwestern Uganda), and compare them to surrounding savanna-grassland values. We compare these environmental values to strontium isotopes ratios in faunal tooth enamel to determine if habitat preferences are accurately reflected.
Results
Gallery forest and savanna-grassland vegetations have significantly different strontium isotope ratio profiles. We trace these isotopic differences to the influence of the Mugiri tributaries, which originate on Paleoproterozoic gneiss deposits on top of the surrounding escarpments. These isotopic differences in vegetation are mirrored in the tissues of fauna with habitat preferences for either the gallery forest or the surrounding grasslands.
Discussion
This research demonstrates the potential of strontium isotope ratios to identify habitat preferences in modern or fossil fauna under proper geologic variability. It provides a methodological model for future studies seeking to reconstruct habitat preferences in early hominins.