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First record of a bivalved larval shell in Early Cambrian tommotiids and its phylogenetic significance
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.
Department of Biological Sciences, Macquarie University, North Ryde, NSW 2109, Australia.
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2011 (English)In: Palaeontology, ISSN 0031-0239, E-ISSN 1475-4983, Vol. 54, no 2, 235-239 p.Article in journal (Refereed) Published
Abstract [en]

Brachiopods are marine Lophotrochozoa whose soft parts are enclosed in a bivalved shell. Although brachiopods are represented by a rich record from the Early Cambrian to the present, the origin of their bivalved body plan remains controversial. The Early Cambrian organophosphatic tommotiids Micrina and Paterimitra from Australia have been proposed as stem brachiopods. Here, we describe their earliest ontogeny, indicating that tommotiids possessed bivalved planktotrophic larvae. The curious combinations of characters in Micrina and Paterimitra indicate that they may belong to the stems of the Linguliformea and Rhynchonelliformea, respectively. The bivalved shell of adult living brachiopods may represent a plesiomorphic character retained from planktic tommotiid larvae; the crown group body plan of the Brachiopoda may have evolved through the paedomorphic retention of a bivalved larval state.

Place, publisher, year, edition, pages
2011. Vol. 54, no 2, 235-239 p.
Keyword [en]
Early Cambrian, Micrina, Paterimitra, tommotiid, ontogeny, Brachiopoda, Australia
National Category
Earth and Related Environmental Sciences
URN: urn:nbn:se:uu:diva-150724DOI: 10.1111/j.1475-4983.2010.01030.xISI: 000288448800001OAI: oai:DiVA.org:uu-150724DiVA: diva2:408545
Available from: 2011-04-05 Created: 2011-04-05 Last updated: 2013-01-23Bibliographically 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.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 967
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
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)
Available from: 2012-09-27 Created: 2012-08-31 Last updated: 2013-01-23Bibliographically approved

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