Academic literature on the topic 'Fossils'

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Dissertations / Theses on the topic "Fossils"

1

Van, Dijk D. E. "Contributions to knowledge of some Southern African fossil sites and their fossils /." Link to the online version, 2000. http://hdl.handle.net/10019/3561.

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2

Van, Dijk D. E. "Contributions to knowledge of some Southern African fossil sites and their fossils." Thesis, Stellenbosch : University of Stellenbosch, 2001. http://hdl.handle.net/10019.1/2988.

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Thesis (MSc (Botany and Zoology. Palaeontology))--University of Stellenbosch, 2001.<br>The fossil sites and fossils reported here range from the Archaean to the Recent. Information is presented on the circumstances of the discovery of some fossil sites in Southern Africa. A number of fossil sites, some of which can no longer be studied, are photographically recorded. Some recorded sites were relocated, while failure to locate others is noted. The assemblages at selected fossil sites are compiled, including some additions to their floras and faunas. Certain individual fossils are illustrated and discussed. Techniques which are not standard are outlined.
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3

Rydin, Catarina. "The Gnetales : fossils and phylogenies /." Stockholm : Department of Botany, Stockholm University, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-488.

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4

Brocks, Jochen J. "Molecular fossils in Archean rocks." Phd thesis, School of Geosciences, 2001. http://hdl.handle.net/2123/14300.

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5

Mounce, Ross. "Comparative cladistics : fossils, morphological data partitions and lost branches in the fossil tree of life." Thesis, University of Bath, 2013. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.642021.

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In this thesis I attempt to gather together a wide range of cladistic analysis of fossil and extant taxa representing a diverse array of phylogenetic groups. I use this data to quantitatively compare the effect of fossil taxa relative to extant taxa in terms of support for relationships, number of most parsimonious trees (MPTs) and leaf stability. In line with previous studies I find that the effects of fossil taxa are seldom different to extant taxa – although I highlight some interesting exceptions. I also use this data to compare the phylogenetic signal within vertebrate morphological data sets, by choosing to compare cranial data to postcranial data. Comparisons between molecular data and morphological data have been previously well explored, as have signals between different molecular loci. But comparative signal within morphological data sets is much less commonly characterized and certainly not across a wide array of clades. With this analysis I show that there are many studies in which the evidence provided by cranial data appears to be be significantly incongruent with the postcranial data – more than one would expect to see just by the effect of chance and noise alone. I devise and implement a modification to a rarely used measure of homoplasy that will hopefully encourage its wider usage. Previously it had some undesirable bias associated with the distribution of missing data in a dataset, but my modification controls for this. I also take an in-depth and extensive review of the ILD test, noting it is often misused or reported poorly, even in recent studies. Finally, in attempting to collect data and metadata on a large scale, I uncovered inefficiencies in the research publication system that obstruct re-use of data and scientific progress. I highlight the importance of replication and reproducibility – even simple re-analysis of high profile papers can turn up some very different results. Data is highly valuable and thus it must be retained and made available for further re-use to maximize the overall return on research investment.
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6

Herman, Julie D. "Fossil preservation and the effects of groundwater leaching on fossils in the Yorktown Formation (Upper Pliocene), Virginia." Thesis, Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/90972.

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Patterns of fossil diagenesis caused by groundwater leaching provide insight into how shells are altered. This study analyzes fossils in unconsolidated terrigenous sediments from the Virginia Coastal Plain, unlike previous studies conducted mostly in carbonate terranes. The vertical and lateral distribution of diagenetic states was mapped in an outcrop (63 m by 2.1 m) of the Yorktown Formation. A paleostream channel located at one end was incised during the Pleistocene and filled with sediments of the Shirley Formation. The Tabb Formation unconformably overlies the outcrop. Acidic groundwater caused the observed patterns of fossil and sediment diagenesis. These patterns include zones of fossil alteration, diagenetic stratification of the sediment, and fossil diagenesis on a microstructural level. Groundwater movement, controlled by the presence of the paleochannel, caused diagenetic alteration or complete dissolution of the fossils, and possibly caused precipitation of fine-grained iron oxyhydroxides. All carbonate material in the vicinity of the paleochannel is completely dissolved away, although iron oxyhydroxide coatings of fossils remain. Away from the paleochannel Crepidula fornicata (gastropod; aragonite), Ostrea sp. (bivalve; calcite), Balanus sp. (barnacle; calcite), and bryozoans (calcite) are found in parallel zones of alteration that dip toward the paleochannel and cut across horizontal sedimentologic and fossiliferous layers. Groundwater also leached the Yorktown sediments. This alteration caused a diagenetic stratification of the sediment, with unaltered greenish-gray silty fine sand along the base of the outcrop, overlain by leached yellowish-brown silty fine sand and areas of concentrated iron oxyhydroxides. The preservation of both aragonitic and calcitic shells was affected by groundwater movement. Original aragonitic shell material is found as chalky, uncrystallized specimens or neomorphosed shells, or is completely dissolved with only molds or ghosts remaining. Neomorphosed specimens typically consist of calcite-replaced shell material with pockets of original aragonite, and sparry calcite filling empty shell cavities. Original calcitic shell material is either chalky or unaltered. Chalky shells range from relatively hard to soft and pasty. Crepidula shells of intermediate chalkiness tend to separate into thin flakes, caused by dissolution along growth surfaces. Chalkiness of pasty shells is caused by dissolution of shell material (without recrystallization) and not simply loss of organic matrix. SEM photos of Crepidula reveal the more porous and leached appearance of chalky shells in contrast with hard; unaltered shells. The presence of chalky aragonitic and calcitic shells indicates that chalky textures are, to some degree, independent of mineralogy and microstructure.<br>M.S.
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7

Buckman, James O. "Lower Carboniferous trace fossils from northwest Ireland." Thesis, Queen's University Belfast, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262648.

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8

Legg, David. "The impact of fossils on arthropod phylogeny." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/24168.

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The arthropods are the most diverse, abundant and ubiquitous phylum on Earth. Five main extant groups (subphyla) can be recognized: Pycnogonida, Euchelicerata, Myriapoda, Hexapoda, and Crustacea. Each group displays a distinctive body plan and a suite of autapomorphies that makes determining their interrelationships difficult. Although a variety of hypotheses have been proposed regarding their interrelationships, just three have frequently been recovered in recent phylogenetic analyses. Rather than representing incongruent topologies these hypotheses represent variations of the position of the root on the same parent topology. The long histories of the major arthropod subclades, which had begun to diverge by, at least, the early Cambrian, means that long-branch artefacts are highly probable. To alleviate potential long-branch attraction and provide a more accurate placement of the root, 214 fossil taxa were coded into an extensive phylogenetic data set of 753 discrete characters, which also includes 95 extant panarthropods and two cycloneuralian outgroups. Preference was given to those fossil taxa thought to occur during the cladogenesis of the major arthropod clades, i.e. the lower and middle Cambrian. An extensive study of material from the middle Cambrian Burgess Shale Formation and the coeval Stephen Formation in British Columbia (Canada) was undertaken. This study focussed primarily on taxa thought to represent 'upper stem-group euarthropods', namely bivalved arthropods and megacheirans ('great-appendage' arthropods), as they will have the greatest utility in polarizing relationships within the arthropod crown-group [= Euarthropoda]. This study includes the description of three new genera and four new species: the bivalved arthropods Nereocaris exilis, N. briggsi, and Loricicaris spinocaudatus; and the megacheiran Kootenichela deppi; and a restudy selected material referred to the bivalved arthropod taxa Isoxys, Canadaspis perfecta, Odaraia alata and Perspicaris dictynna. Results of the phylogenetic analysis and additional perturbation tests confirm the utility of these taxa for polarizing relationships within Euarthropoda and reducing long-branch artefacts. For example, the hexapods were recovered within a paraphyletic Crustacea, a result anticipated by molecular phylogenetic analyses but until now elusive in morphological phylogenies. Perturbation tests indicate that close affinities of myriapods and hexapods, a result common in morphological analyses, is the result of a long-branch artefact caused by the convergent adaptation to a terrestrial habit, which is broken by the addition of fossil material. The phylogeny provides a detailed picture of character acquisition in the arthropod stem group.
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9

Cooper, Robert D. "A knowledge-based system for hominid fossils." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0004420.

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10

Friend, Duncan. "Palaeobiology of Palaeozoic medusiform stem group echinoderms." Thesis, University of Cambridge, 1995. https://www.repository.cam.ac.uk/handle/1810/265414.

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The morphological details of both external and internal anatomy of a group of Palaeozoic fossil medusiform animals are described with the aid of text-figures and plates with explanatory drawings. This fossil group had a worldwide distribution with a stratigraphic range from the Lower Cambrian to the Upper Devonian and includes the following taxa:- Eldonia ludwigi Walcott 1911, E. eumorphus sp. nov., Rotadiscus grandis Sun and Hou 1987, Discophylluni peltatum Hall 1847, D. mirabile Chapman 1926, D. cryptophya (Clarke) 1900. Newly recognised anatomical structures for E. ludwigi include c.30, internal, radially-arranged, bifurcating lobes, a coelomic sac surrounding the alimentary canal, internal structures assumed to represent gonads and c.4 oral tentacles. E. eumorphus has c.44 internal bifurcating lobes associated with rows of pores on the ventral surface, which form a possible respiratory system. R. granclis has a possibly mineralised dorsal surface, rows of pores on the ventral surface and a tentacular appendage with arm-like extensions. Discophylluni 1s characterised by an ornamented dorsal surface with rows of elaborate pores. The nomenclature 1s revised, anatomical reconstructions are presented and modes of life in terms of feeding and benthic versus pelagic existence are discussed. It is concluded that this group, the Discophylla (equivalent in status to a new class), lies within the stem group Echinodermata. As a consequence, current understanding of the early evolution of the Echinodermata, especially with respect to internal anatomy, is questioned . A number of medusiforrn fossils, not studied in detail as part of this work, are discussed and tentatively assigned to the Discophylla.
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