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Early Cambrian Problematic Lophotrochozoans and Dilemmas of Scleritome Reconstructions

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Early Cambrian Problematic Lophotrochozoans and Dilemmas of Scleritome Reconstructions Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 967 Early Cambrian Problematic Lophotrochozoans and Dilemmas of Scleritome Reconstructions CECILIA M LARSSON ACTA UNIVERSITATIS UPSALIENSIS ISSN 1651-6214 ISBN 978-91-554-8462-0 UPPSALA urn:nbn:se:uu:diva-180195 2012 Dissertation presented at Uppsala University to be publicly examined in Hambergsalen, Geocentrum, Villavägen 16, Uppsala, Friday, October 19, 2012 at 09:00 for the degree of Doctor of Philosophy. The examination will be conducted in English. Abstract Larsson, C. M. 2012. Early Cambrian Problematic Lophotrochozoans and Dilemmas of Scleritome Reconstructions. Acta Universitatis Upsaliensis. Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 967. 47 pp. Uppsala. ISBN 978-91-554-8462-0. 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. Keywords: Problematica, scleritome, Trachyplax, tommotiid, Cambrian, South Australia, North Greenland Cecilia M Larsson, Uppsala University, Department of Earth Sciences, Palaeobiology, Villav. 16, SE-752 36 Uppsala, Sweden. © Cecilia M Larsson 2012 ISSN 1651-6214 ISBN 978-91-554-8462-0 urn:nbn:se:uu:diva-180195 (http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-180195) Jocke Selma Fanny List of Papers This thesis is based on the following papers, referred to in the text by their Roman numerals. I Larsson, C.M., Peel, J.S., Högström, A.E.S. (2009) Trachyplax arctica, a new multiplated problematic fossil from the lower Cambrian of North Greenland. Acta Palaeontologica Polonica, 54(3):513–523 doi: http://dx.doi.org/10.4202/app.2009.0026 II Skovsted, C.B., Holmer, L.E., Larsson, C.M., Högström, A.E.S., Brock, G.A., Topper, T.P., Balthasar, U., Pettersson Stolk, S., Paterson, J.R. (2009) The scleritome of Paterimitra: an Early Cambrian stem group brachiopod from South Australia. Proceedings of the Royal Society of London B, 276 (1662):1651-1656 III Holmer, L.E., Skovsted, C.B., Larsson, C.M., Brock, G.A., Zhang, Z. (2011) First record of a bivalved larval shell in early Cambrian tommotiids and its phylogenetic significance. Palaeontology, 54 (2):235-239 IV Topper, T.P., Holmer, L.E., Skovsted, C.B., Brock, G.A., Balthasar, U., Larsson, C.M., Pettersson Stolk, S., Harper, D.A.T. (in press). The oldest brachiopods from the lower Cambrian of South Australia. Acta Palaeontologica Polonica. doi: http://dx.doi.org/10.4202/app.2011.0146 V Larsson, C.M., Skovsted, C.B., Brock, G.A., Balthasar, U., Holmer, L.E., Topper, T.P. (manuscript submitted to Palaeontology) Paterimitra pyramidalis from South Australia; Scleritome, shell structure and evolution of a lower Cambrian stem group brachiopod. VI Larsson, C.M. (manuscript prepared for submission to Journal of Paleontology) Revision of the tommotiid Kulparina rostrata (Conway Morris & Bengtson in Bengtson et al., 1990) from South Australia. Articles are reproduced with permission from the respective copyright holders. Papers I and IV © Institute of Palaeontology, Polish Academy of Sciences Paper II, V and VI © The authors Paper III © Palaeontological Association/Wiley-Blackwell Publishing Ldt Statement of authorship Paper I: C.M.L. photographed the material and produced the tables and Figs 2-7, participated in the analysis and wrote the main part of the manuscript. Paper II: C.M.L. took part in recent field work, processing of material and SEM work, contributed to analysis and manuscript preparation. Paper III: C.M.L. took part in recent field work, processing of material and SEM work, contributed to interpretations and preparation of the final version of the manuscript. Paper IV: C.M.L. assisted in field work and participated in manuscript preparation. Paper V: C.M.L. took part in recent field work, processing of samples and picking of residues, conducted the majority of SEM work, completed the analysis and scleritome reconstruction, wrote the main part of the manuscript and produced all tables as well as Figs 2-17 and 21. Paper VI: C.M.L. participated in picking of residues, conducted SEM work, produced all figures, and wrote the manuscript. Disclaimer The papers and manuscripts presented herein are for the purpose of public examination as a doctoral thesis only. They are not deemed valid for taxonomic or nomenclatural purposes [see article 8.2 in the International Code of Zoological Nomenclature]. Accordingly, all new taxonomic names and emendations are void, and authority for taxonomic work is retained by the original publications. Contents 1. Introduction ................................................................................................. 9 The 'Cambrian Explosion' – early evolution of animals ............................. 9 Sclerites, scleritomes and reconstructions ................................................ 10 Building a house without a blueprint ....................................................... 12 'Problematica' and problematic lophotrochozoans ................................... 15 Aims of this PhD thesis ............................................................................ 17 2. Multiplated enigmas from North Greenland ............................................. 18 Trachyplax arctica Larsson, Peel & Högström, 2009 .............................. 18 3. South Australian tommotiids and the evolution of paterinid brachiopod shell structures .............................................................................................. 22 Tommotiids from South Australia ............................................................ 24 Paterimitra pyramidalis – a stem-group brachiopod ............................... 26 Askepasma, Paterimitra and the evolution of the paterinid brachiopod shell structure ........................................................................................... 28 Kulparina rostrata: 1+1=1 ....................................................................... 30 4. Svensk sammanfattning ............................................................................ 33 Den kambriska explosionen – djurlivets tidiga evolution .................... 33 Skleriter, skleritom och rekonstruktioner – att bygga ett hus utan ritningar ............................................................................................... 34 'Problematica' och lofotrochozoer ....................................................... 35 Avhandlingens syfte ............................................................................ 36 Trachyplax arctica från Nordgrönland ................................................ 36 Tommotiider från södra Australien och evolutionen av skalstrukturen hos paterinida brachiopoder ......................................... 37 5. Acknowledgements ................................................................................... 39 6. References ................................................................................................. 40 1. Introduction The 'Cambrian Explosion' – early evolution of animals
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