28 research outputs found

    Luminescence dating and geochemistry constraints on late Pleistocene hydrological and ecological change for north-eastern Australia

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    Extensive debate surrounds the timing and cause of late Pleistocene megafauna extinction across the continent of Sahul (Australia and New Guinea). Central to these debates is uncertainty in the timing and impact of key events during the last glacial cycle (125 – 12 thousand years ago; ka) including the arrival of humans on the continent, the effect climate change had on environments, and the geographical and temporal patterns of megafauna extinction. This uncertainty can be attributed to the lack of well-constrained palaeoenvironmental records, limited spatial coverage and dating reliability. To address these knowledge gaps, this thesis applies geochronological and geochemical techniques to a series of new palaeoenvironmental archives to investigate megafauna extinction in the context of climate-induced environmental change. Chapters 2 and Chapter 3 of the thesis present optically stimulated luminescence (OSL) and radiocarbon (14C) dating results on palaeoenvironmental archives (sediment cores) from two subtropical wetlands (Welsby Lagoon, Chapter 2; Brown Lake, Chapter 3). Analysis of twenty-one OSL ages and seven 14C ages from Welsby Lagoon (Chapter 2) highlights the importance of carefully considering the material being dated, especially where contamination is likely. In general, 14C ages derived from identifiable terrestrial plant macrofossils agree with OSL ages, while 14C results derived from unidentifiable plant remains and charcoal are scattered and produce stratigraphic inversions. The need to consider different sediment accumulation histories on a site-by-site basis is also demonstrated in Chapter 2 and Chapter 3 using Bayesian modelling. Further geochronological results are reported in Chapters 4 and Chapter 5, which combine OSL, ESR and U-series dating to establish megafauna last appearance at the new tropical megafauna fossil locality of South Walker Creek, Queensland (Chapter 4 & Chapter 5). Hierarchical Bayesian modelling – which incorporates 66 new ages from eight sites – is used to provide new evidence for megafauna disappearance in the Fitzroy River catchment between 41.7 and 35.8 ka (95 % C.I.; Chapter 5). Additionally, hierarchical Bayesian modelling of fluvial and fossil deposits at the South Walker Creek fossil locality indicates a decrease in hydrological activity in the area during mid- to late- Marine Isotope Stage 3 (MIS3) (Chapter 5). The comprehensive dating approach presented in each study (Chapters 2 – 5) enables improved examination of the spatiotemporal pattern of climate-induced environmental change taking place across eastern Australia immediately prior to, during, and after, megafauna disappearance (Chapter 5). Alignment of XRF and age data from Welsby Lagoon shows two phases of increased dust deposition at 71 – 67 ka and 58 – 48 ka (Chapter 2) – the latter coinciding with the wetland transitioning from a lake to swamp. Brown Lake also experienced an increase in dust deposition through late MIS3, in addition to entering a phase of shoreline regression lasting until the Holocene (Chapter 3). Notably, when these sites are included in a regional spatiotemporal synthesis of hydrological activity (compiling data from other wetlands and regional catchments) and are considered in the context of local megafauna records (Chapter 4), there is evidence to suggest megafauna disappearance in the Fitzroy River Basin catchment was coincident with broader environmental change during mid- to late- MIS3 (Chapter 5). This thesis employs a robust, geochronologically driven approach to examine ecological and environmental change during significant and understudied periods of Australian prehistory (e.g., pre- LGM). The overarching conclusion is that there is little support for rapid or synchronous human-mediated, continent-wide megafauna extinction during the late Pleistocene. Rather, the data suggest extinction coincided with a period of prolonged hydroclimate deterioration initiated during the mid- to late-MIS3.Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 202

    The Deep Evolution of Ecdysozoa

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    Ecdysozoa (moulting animals) comprises the protostome Phyla Arthropoda, Kinorhyncha, Loricifera, Nematoda, Nematomorpha, Onychophora, Priapulida and Tardigrada, but our precise understanding of the phylogenetic relationships between these is disputed. Ecdysozoa is an extremely ancient clade that originated in the oceans, and ecdysozoans remain major components of modern marine and terrestrial ecosystems, including the most diverse and abundant of all animal Phyla (Arthropoda and Nematoda respectively). In this thesis, I explore the phylogenetic relationships and divergence times of fossil and extant ecdysozoans in order to address several outstanding issues in the early evolutionary history and palaeobiology of Ecdysozoa, employing data from fossils and molecular sequences. First, the phylogenetic relationships of the eight ecdysozoan phyla was tested using Bayesian models from a molecular matrix containing newly sequenced taxa from Nematomorpha, Priapulida and Tardigrada. Analyses retrieved a monophyletic Scalidophora (Kinorhyncha, Loricifera and Priapulida) which in turn is sister-group to a clade comprising Nematoida (Nematoda and Nematomorpha) and Panarthropoda (Arthropoda, Onychophora and Tardigrada) – this is named Cryptovermes nov. An improved set of fossil calibrations was compiled and used to infer the divergence times of ecdysozoans under a range of alternative parameters. Crown-group Ecdysozoa diverged in the Ediacaran Period between 636 – 578 Ma, at least 23 million years before the oldest potential fossil evidence of ecdysozoans in the late Ediacaran (<556 Ma). Arthropods show more precision and less incongruence with the fossil record compared to other ecdysozoan phyla. Several vermiform (worm-like) fossils from the exceptionally preserved Cambrian Stage 3 Chengjiang Biota of Yunnan Province, south-western China were investigated to address the origin of Ecdysozoa and Panarthropoda in a morphological phylogenetic context. Phylogenetic analyses placed Acosmia maotiania in stem-group Ecdysozoa. Ancestral character state reconstructions revealed the similarities and contrasts between the stem-group ecdysozoan A. maotiania and a reconstruction of the common ancestor of crown-group Ecdysozoa. This reveals that pharyngeal teeth and circumoral armament are likely to be derived traits of the ecdysozoan crown-group, and may have 3 influenced the diversification of crown-group ecdysozoans – perhaps facilitating a change in feeding style (e.g. predation). The cycloneuralians Tabelliscolex hexagonus, Cricocosmia jinningensis and Mafangscolex yunnanensis (=Palaeoscolecidomorpha nov.) share several characters in common with lobopodian panarthropods. This includes paired, seriated ventral trunk structures, corresponding (in T. hexagonus and C. jinningensis) to seriated lateral/dorsolateral trunk sclerites with a net-like microstructure. However, phylogenetic analyses did not retrieve a relationship between palaeoscolecidomorphs and panarthropods, indicating that this style of morphological seriation may have multiple origins within Ecdysozoa. The lobopodian Facivermis yunnanicus is rejected as a model system to understand the acquisition a segmental bodyplan with paired appendages in Panarthropoda. Phylogenies generated here indicate that F. yunnanicus’ worm-like appearance is secondarily adapted from more typical lobopodian ancestors, as a result of adaptation to a specialised tube-dwelling suspension-feeding ecology. Finally, the phylogenetic relationships and divergence times of chelicerate arthropod groups were inferred, and interpreted in the context of arthropod terrestrialization. Phylogenetic analysis of a highly complete matrix of slowly evolving genes supports the monophyly of arachnids. Furthermore, it is parsimonious that the common ancestor of scorpions and other air-breathing arachnids was terrestrial – or at least amphibious – if arachnids are a monophyletic group. Molecular clocks estimate that arachnids diverged in the Cambrian or Early Ordovician, though body fossils of these arthropods are absent until the Silurian which supports the hypothesis of paleontologically cryptic early terrestrial biosphere – mirrored by the molecular and fossil records of myriapods and land plants. Scorpions are the oldest extant terrestrial chelicerate lineage in the fossil record, but is unclear whether the earliest Silurian examples were marine, terrestrial, or even secondarily marine in life

    Finding banded patternsin large data set using segmentation

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    The University of Iowa 2020-21 General Catalog

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    The University of Iowa 2019-20 General Catalog

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    Reconstructing Landscape Use Patterns Using Strontium Isotope Ratios

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    This dissertation uses modern habitats and fauna to model the variability and predictive power of strontium isotope ratios in identifying dispersal patterns in primates and habitat preference in primate and non-primate fauna. It concludes that there are significant isotopic differences between gallery forest and xeric grassland habitats in the same area and that these differences are reflected in fauna with habitat preferences for one or the other. It also identifies the most reliable methodological approaches for identifying the philopatric and dispersing sex in primate communities. Finally, it applies this methodological recommendation to strontium isotope data from South African hominins, concluding that both Australopithecus africanus and Australopithecus robustus followed patterns of female dispersal and male philopatry while also suggesting a larger home range size for A. africanus

    The University of Iowa 2018-19 General Catalog

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    The University of Iowa 2017-18 General Catalog

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    The University of Iowa General Catalog 2016-17

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