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Trachyplax arctica, a new multiplated probelematic fossil from the lower Cambrian of North Greenland
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.
2009 (English)In: Acta Palaeontologica Polonica, ISSN 0567-7920, Vol. 54, no 3, 513-523 p.Article in journal (Refereed) Published
Abstract [en]

A new scleritome-bearing organism with eight sclerite types, Trachyplax   arctica gen. et sp. nov., is described from the lower Cambrian   Paralledal Formation of North Greenland. The originally calcareous   sclerites are now silicified; no microstructures are preserved. The   dominant sclerite type (A; maximum dimension 19.3 mm) is bilaterally   symmetrical, strongly arched, with an oval shield showing co-marginal   growth lines and a projecting rostrum with prominent radial   ornamentation. A similar sclerite morphology can be identified in   Silurian-Carboniferous multiplacophoran molluscs but the remaining   sclerite types, which also display a combination of concentric and   radial ornamentation, find no clear equivalents. Two models for   scleritome reconstruction are presented, based on the relative   abundance of the sclerites, but neither promotes a satisfactory   assignment to a higher taxon. Despite the morphological   dissimilarities, possibly reflecting the age discrepancy, reference to   the Multiplacophora is most attractive and entails a substantial   extension of the known geological range of that group.

Place, publisher, year, edition, pages
2009. Vol. 54, no 3, 513-523 p.
Keyword [en]
Trachyplax, Problematica, sclerites, scleritome, Multiplacophora, Cambrian, Greenland
National Category
Earth and Related Environmental Sciences
Research subject
Historical Geology and Paleontology
Identifiers
URN: urn:nbn:se:uu:diva-108294DOI: 10.4202/app2009.0026ISI: 000270574400014OAI: oai:DiVA.org:uu-108294DiVA: diva2:235161
Available from: 2009-09-14 Created: 2009-09-14 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.
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)
Opponent
Supervisors
Available from: 2012-09-27 Created: 2012-08-31 Last updated: 2013-01-23Bibliographically approved

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