Ontogeny, Intraspecific Variation, and Systematics of the Late Cambrian Trilobite Dikelocephalus
Ontogeny, Intraspecific Variation, and Systematics of the Late Cambrian Trilobite Dikelocephalus

Author: Nigel C. Hughes

Publisher:

Published: 1994

Total Pages: 728

ISBN-13:

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Biometric analyses of well-localized specimens of the trilobite Dikelocephalus from the St. Lawrence Formation (Upper Cambrian), northern Mississippi Valley, suggest that all specimens belong to a single, highly variable morphospecies, D. minnesotensis. A complex pattern of ontogenetically-related and ontogeny-independent variation produced a mosaic of morphotypes, which show greater diversity than previously recorded within trilobite species. There is considerable variation within collections made from single beds. Variations of characters among collections are mosaic, and are clinal in some cases. Patterns of variation within Dikelocephalus cannot be related to lithofacies occurrence. There are no obvious temporal variations in D. minnesotensis within the St. Lawrence Formation, but some Dikelocephalus from the underlying Tunnel City Group may belong to a different taxon. The validity of this early taxon is questionable due to a lack of available material. The mosaic pattern of variation in Dikelocephalus mimics that documented at higher taxonomic levels in primitive libristomate trilobites, and helps explain difficulties in providing a workable taxonomy of primitive trilobites. Results caution proposition of evolutionary scenarios that do not take account of intraspecific variation. The recovery of dorsal shields of Dikelocephalus permits the first detailed reconstruction of the entire exoskeleton. The systematics of the genus is revised and twenty-five species are suppressed as junior synonyms of D. minnesotensis.

The Evolution and Fossil Record of Parasitism
The Evolution and Fossil Record of Parasitism

Author: Kenneth De Baets

Publisher: Springer Nature

Published: 2022-01-01

Total Pages: 487

ISBN-13: 3030522334

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This two-volume edited book highlights and reviews the potential of the fossil record to calibrate the origin and evolution of parasitism, and the techniques to understand the development of parasite-host associations and their relationships with environmental and ecological changes. The book deploys a broad and comprehensive approach, aimed at understanding the origins and developments of various parasite groups, in order to provide a wider evolutionary picture of parasitism as part of biodiversity. This is in contrast to most contributions by parasitologists in the literature that focus on circular lines of evidence, such as extrapolating from current host associations or distributions, to estimate constraints on the timing of the origin and evolution of various parasite groups. This approach is narrow and fails to provide the wider evolutionary picture of parasitism on, and as part of, biodiversity. Volume two focuses on the importance of direct host associations and host responses such as pathologies in the geological record to constrain the role of antagonistic interactions in driving the diversification and extinction of parasite-host relationships and disease. To better understand the impact on host populations, emphasis is given to arthropods, colonial metazoans, echinoderms, mollusks and vertebrates as hosts. In addition, novel techniques used to constrain interactions in deep time are discussed ranging from chemical and microscopic investigations of host remains, such as blood and coprolites, to the statistical inference of lateral transfer of transposons and host-parasite coevolutionary dynamics using molecular divergence time estimation.

Numerical Palaeobiology
Numerical Palaeobiology

Author: D. A. T. Harper

Publisher: John Wiley & Sons

Published: 1999-07-09

Total Pages: 488

ISBN-13:

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Numerical Palaeobiology Computer-Based Modelling and Analysis of Fossils and their Distributions Edited by David A.T. Harper University of Copenhagen, Denmark Microcomputers have become an everyday part of the palaeobiologists tool-kit. Moreover, there is now a wide range of computer software available to handle all sorts of palaeontological data and problems. This book, aimed at final year undergraduates, graduate students and professional palaeontologists, biologists and geologists, brings together the many strands of contemporary palaeontology through the medium of numeracy. It provides a comprehensive review, with applications, of the many computer based techniques available for the analysis and modelling of palaeontological data. The first part of the book covers classical phenetic taxonomy through cladistics and the computer-generated reconstructions of fossils to actual models for fossil growth. This leads onto distribution analysis and modelling of fossils in time and space. Detailed stratigraphical distributions of fossils are described in quantitative terms together with the larger-scale patterns in the history of life itself, while palaeoecology, palynofacies, trace fossils and palaeogeography are all introduced through a spectrum of numerical algorithms. The majority of the studies are linked to specific software packages and many are illustrated with case histories. Although there are a number of books available on computer modelling and data analysis in geology, no study has integrated the two with such a range of palaeontological subject material.