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      Phylogenetic and Biogeographic Analysis of Sphaerexochine Trilobites

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      PLoS ONE
      Public Library of Science

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          Abstract

          Background

          Sphaerexochinae is a speciose and widely distributed group of cheirurid trilobites. Their temporal range extends from the earliest Ordovician through the Silurian, and they survived the end Ordovician mass extinction event (the second largest mass extinction in Earth history). Prior to this study, the individual evolutionary relationships within the group had yet to be determined utilizing rigorous phylogenetic methods. Understanding these evolutionary relationships is important for producing a stable classification of the group, and will be useful in elucidating the effects the end Ordovician mass extinction had on the evolutionary and biogeographic history of the group.

          Methodology/Principal Findings

          Cladistic parsimony analysis of cheirurid trilobites assigned to the subfamily Sphaerexochinae was conducted to evaluate phylogenetic patterns and produce a hypothesis of relationship for the group. This study utilized the program TNT, and the analysis included thirty-one taxa and thirty-nine characters. The results of this analysis were then used in a Lieberman-modified Brooks Parsimony Analysis to analyze biogeographic patterns during the Ordovician-Silurian.

          Conclusions/Significance

          The genus Sphaerexochus was found to be monophyletic, consisting of two smaller clades (one composed entirely of Ordovician species and another composed of Silurian and Ordovician species). By contrast, the genus Kawina was found to be paraphyletic. It is a basal grade that also contains taxa formerly assigned to Cydonocephalus. Phylogenetic patterns suggest Sphaerexochinae is a relatively distinctive trilobite clade because it appears to have been largely unaffected by the end Ordovician mass extinction. Finally, the biogeographic analysis yields two major conclusions about Sphaerexochus biogeography: Bohemia and Avalonia were close enough during the Silurian to exchange taxa; and during the Ordovician there was dispersal between Eastern Laurentia and the Yangtze block (South China) and between Eastern Laurentia and Avalonia.

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          Most cited references60

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          Glacio-Eustatic Control of Late Ordovician–Early Silurian Platform Sedimentation and Faunal Changes

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            An Annotated Linnaean Hierarchy, with Comments on Natural Taxa and Competing Systems

            E. Wiley (1979)
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              Post-cambrian trilobite diversity and evolutionary faunas

              A cluster analysis of the stratigraphic distribution of all Ordovician trilobite families, based on a comprehensive taxonomic database, identified two major faunas with disjunct temporal diversity trends. The Ibex Fauna behaved as a cohort, declining through the Ordovician and disappearing at the end-Ordovician mass extinction. In contrast, the Whiterock Fauna radiated rapidly during the Middle Ordovician and gave rise to all post-Ordovician trilobite diversity. Its pattern of diversification matches that of the Paleozoic Evolutionary Fauna; hence, trilobites were active participants in the great Ordovician radiations. Extinction patterns at the end of the Ordovician are related to clade size: Surviving trilobite families show higher genus diversity than extinguished families.
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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS One
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, USA )
                1932-6203
                2011
                27 June 2011
                : 6
                : 6
                : e21304
                Affiliations
                [1]Department of Geology and Biodiversity Institute, University of Kansas, Lawrence, Kansas, United States of America
                Field Museum of Natural History, United States of America
                Author notes

                Conceived and designed the experiments: CRC BSL. Performed the experiments: CRC. Analyzed the data: CRC. Contributed reagents/materials/analysis tools: CRC BSL. Wrote the paper: CRC BSL.

                Article
                PONE-D-11-04926
                10.1371/journal.pone.0021304
                3124496
                21738632
                5e601b17-b95a-49f8-898f-63fcc7f6b18d
                Congreve, Lieberman. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
                History
                : 15 March 2011
                : 25 May 2011
                Page count
                Pages: 11
                Categories
                Research Article
                Biology
                Evolutionary Biology
                Evolutionary Systematics
                Taxonomy
                Animal Taxonomy
                Cladistics
                Paleontology
                Invertebrate Paleontology

                Uncategorized
                Uncategorized

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