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The scleritome of Paterimitra: an Early Cambrian stem group brachiopod from South Australia
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
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2009 (English)In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 276, no 1662, 1651-1656 p.Article in journal (Refereed) Published
Abstract [en]

Early Cambrian tommotiids are problematic fossil metazoans with external organophosphatic sclerites that have been considered to be basal members of the lophophorate stem group. Tommotiids are almost exclusively known from isolated or rarely fused individual sclerites, which made previous reconstructions of the actual organism highly conjectural. However, the recent discovery of the first articulated specimens of the tommotiid Eccentrotheca revealed a tubular sclerite arrangement (scleritome) that limited the possible life habit to sessile filter feeding and thus further supported a lophophorate affinity. Here, we report the first articulated specimens of a second tommotiid taxon, Paterimitra from the Early Cambrian of the Arrowie Basin, South Australia. Articulated specimens of Paterimitra are composed of two bilaterally symmetrical sclerite types and an unresolved number of small, asymmetrical and irregular crescent-shaped sclerites that attached to the anterior margin of the symmetrical sclerites. Together, the sclerites form an open cone in which the symmetrical sclerites are joined together and form a small posterior opening near the base of the scleritome, while the irregular crescent-shaped sclerites defined a broad anterior opening. The coniform scleritome of Paterimitra is interpreted to have attached to hard substrates via a pedicle that emerged through the small posterior opening ( sometimes forming a tube) and was probably a sessile filter feeder. The scleritome of Paterimitra can be derived from the tubular scleritome of Eccentrotheca by modification of basal sclerites and reduction in tube height, and probably represents a more derived member of the brachiopod stem group with the paired symmetrical sclerites possibly homologous to brachiopod valves.

Place, publisher, year, edition, pages
2009. Vol. 276, no 1662, 1651-1656 p.
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-129861DOI: 10.1098/rspb.2008.1655ISI: 000264445000014OAI: oai:DiVA.org:uu-129861DiVA: diva2:345525
Available from: 2010-08-25 Created: 2010-08-25 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Early Cambrian Problematic Lophotrochozoans and Dilemmas of Scleritome Reconstructions
Open this publication in new window or tab >>Early Cambrian Problematic Lophotrochozoans and Dilemmas of Scleritome Reconstructions
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The emergence and radiation of metazoan body plans around the Precambrian/Cambrian boundary, some 500-600 million years ago, seems to be concordant with the appearance and diversification of preservable hard parts. Several Precambrian soft-bodied, multicellular organisms most likely represent stem-group bilaterians, but their fossil record is rather sparse.  In contrast, the Cambrian fossil record is comparably rich – comprising hard part, trace fossil and delicate soft tissue preservation – and most animal phyla that we know of today had evolved by the end of the Cambrian. Consequently, this time represents an important period in the early evolution of metazoan life forms. Most skeletal remnants of invertebrate organisms from this period are preserved in incomplete, disarticulated sclerite assemblages, and the true architecture of the original skeletal structure, the scleritome, may therefore be hard to discern. Many scleritomous taxa have been suggested to be members of the lophotrochozoan clade, while their exact position within this group remains unclear. Such taxa are often referred to as Problematica. This thesis deals with some problematic scleritomous early Cambrian lophotrochozoans, and as such also addresses the dilemmas of scleritome reconstructions. In the first part, completely disarticulated calcareous sclerites from the lower Cambrian of North Greenland are described as Trachyplax arctica. Hypothetical scleritome reconstruction alternatives and comparisons to other scleritome-bearing taxa are discussed, but the lack of articulated material obscures any satisfactory conclusions regarding phylogenetic affinities and the original morphology of the organism. The other part of the thesis focuses on some minute, organophosphatic scleritomous metazoans, tommotiids, found in lower Cambrian limestone successions in South Australia – Paterimitra pyramidalis and Kulparina rostrata – their scleritome architecture and their phylogenetic relationship with paterinid brachiopods. The oldest brachiopod from South Australia, Askepasma saproconcha, and the slightly younger Askepasma toddense are also described and discussed. Based on articulated specimens, recently described partial scleritomes of the tommotiid Eccentrotheca helenia and similarities in shell ultrastructure with both Eccentrotheca and Askepasma, Paterimitra is interpreted as a stem-group brachiopod and reconstructed as a bilaterally symmetrical, sessile, filter feeder with a tubular/conical scleritome. The morphological similarities with Paterimitra point in the same direction for the slightly older Kulparina.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 47 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 967
Keyword
Problematica, scleritome, Trachyplax, tommotiid, Cambrian, South Australia, North Greenland
National Category
Geology Other Earth and Related Environmental Sciences Evolutionary Biology
Research subject
Earth Science with specialization in Historical Geology and Palaeontology
Identifiers
urn:nbn:se:uu:diva-180195 (URN)978-91-554-8462-0 (ISBN)
Public defence
2012-10-19, Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 09:00 (English)
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Available from: 2012-09-27 Created: 2012-08-31 Last updated: 2013-01-23Bibliographically approved

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Skovsted, Christian B.Holmer, Lars E.Larsson, Cecilia M.

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