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Early Cambrian Problematic Lophotrochozoans and Dilemmas of Scleritome Reconstructions
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
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 [en]
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: urn:nbn:se:uu:diva-180195ISBN: 978-91-554-8462-0 (print)OAI: oai:DiVA.org:uu-180195DiVA: diva2:548711
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
List of papers
1. Trachyplax arctica, a new multiplated probelematic fossil from the lower Cambrian of North Greenland
Open this publication in new window or tab >>Trachyplax arctica, a new multiplated probelematic fossil from the lower Cambrian of North Greenland
2009 (English)In: Acta Palaeontologica Polonica, ISSN 0567-7920, E-ISSN 1732-2421, 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.

Keyword
Trachyplax, Problematica, sclerites, scleritome, Multiplacophora, Cambrian, Greenland
National Category
Earth and Related Environmental Sciences
Research subject
Historical Geology and Paleontology
Identifiers
urn:nbn:se:uu:diva-108294 (URN)10.4202/app2009.0026 (DOI)000270574400014 ()
Available from: 2009-09-14 Created: 2009-09-14 Last updated: 2017-12-13Bibliographically approved
2. The scleritome of Paterimitra: an Early Cambrian stem group brachiopod from South Australia
Open this publication in new window or tab >>The scleritome of Paterimitra: an Early Cambrian stem group brachiopod from South Australia
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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.

National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-129861 (URN)10.1098/rspb.2008.1655 (DOI)000264445000014 ()
Available from: 2010-08-25 Created: 2010-08-25 Last updated: 2017-12-12Bibliographically approved
3. First record of a bivalved larval shell in Early Cambrian tommotiids and its phylogenetic significance
Open this publication in new window or tab >>First record of a bivalved larval shell in Early Cambrian tommotiids and its phylogenetic significance
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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.

Keyword
Early Cambrian, Micrina, Paterimitra, tommotiid, ontogeny, Brachiopoda, Australia
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-150724 (URN)10.1111/j.1475-4983.2010.01030.x (DOI)000288448800001 ()
Available from: 2011-04-05 Created: 2011-04-05 Last updated: 2017-12-11Bibliographically approved
4. The oldest brachiopods from the lower Cambrian of South Australia
Open this publication in new window or tab >>The oldest brachiopods from the lower Cambrian of South Australia
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2013 (English)In: Acta Palaeontologica Polonica, ISSN 0567-7920, E-ISSN 1732-2421, Vol. 58, no 1, 93-109 p.Article in journal (Refereed) Published
Abstract [en]

The morphology and organophosphatic shell structure of the paterinate brachiopod Askepasma is documented using new and previously collected specimens from the lower Cambrian of South Australia. Lack of adequately preserved material has seen the majority of paterinate specimens previously reported from South Australia referred to the genus Askepasma and treated under open nomenclature. Large collections of paterinates from the lower Cambrian Wilkawillina, Ajax, and Wirrapowie limestones in the Arrowie Basin, South Australia have prompted redescription of the type species Askepasma toddense and the erection of a new species, Askepasma saproconcha sp. nov. Askepasma saproconcha sp. nov. currently represents the oldest known brachiopod from the lower Cambrian successions in South Australia with a FAD in pre-trilobitic (Terreneuvian, Cambrian Stage 2, lower Atdabanian) strata in the basal part of the Wilkawillina and Wirrapowie limestones. Askepasma toddense predominantly occurs in Abadiella huoi Zone equivalent strata (Unnamed Cambrian Series 2, Stage 3, middle upper Atdabanian) in the upper part of the lower Wilkawillina, Wirrapowie, and Ajax limestones. The shell microstructure of Askepasma suggests a proximal stem group position within the Brachiopoda and similarities with tommotiid taxa provides further evidence that the ancestry of crown group brachiopods is firmly entrenched within the Tommotiida.

Keyword
Brachiopoda, Tommotiida, Paterinida, Askepasma, microstructure, Flinders
National Category
Other Earth and Related Environmental Sciences Geology Evolutionary Biology
Research subject
Earth Science with specialization in Historical Geology and Palaeontology
Identifiers
urn:nbn:se:uu:diva-180189 (URN)10.4202/app.2011.0146 (DOI)000318462900009 ()
Funder
Swedish Research Council, 2012–1658
Available from: 2013-03-13 Created: 2012-08-31 Last updated: 2017-12-07Bibliographically approved
5. Paterimitra pyramidalis from South Australia: Scleritome, shell structure and evolution of a lower Cambrian stem group brachiopod
Open this publication in new window or tab >>Paterimitra pyramidalis from South Australia: Scleritome, shell structure and evolution of a lower Cambrian stem group brachiopod
Show others...
2014 (English)In: Palaeontology, ISSN 0031-0239, E-ISSN 1475-4983, Vol. 57, no 2, 417-446 p.Article in journal (Refereed) Published
Abstract [en]

The tommotiid Paterimitra pyramidalis Laurie, 1986, is redescribed based on well-preserved material from the lower Cambrian Wilkawillina, Wirrapowie and Ajax limestones of the Flinders Ranges, South Australia. The material shows that the scleritome of Paterimitra pyramidalis includes three sclerite morphotypes (S1, S2 and L). Detailed shell microstructure studies show striking similarities with both the paterinid brachiopod Askepasma toddense and the tommotiid Eccentrotheca helenia, which strengthens the suggested evolutionary link between tommotiids and brachiopods. Based on the partly articulated specimens and similarities in shell microstructure and sclerite morphology with Eccentrotheca, Paterimitra pyramidalis is reconstructed as a tube-dwelling, epifaunal, sessile, filter-feeder with an organic pedicle-like attachment structure. The proposed reconstruction of the scleritome comprises a basal unit composed of one S1 and one S2 sclerite, as well as an unresolved number of L sclerites lining a coniform tubular structure.

Keyword
Tommotiida, Brachiopoda, Paterimitra, scleritome structure, lower Cambrian, South Australia
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-180191 (URN)10.1111/pala.12072 (DOI)000332776600009 ()
Funder
The Royal Swedish Academy of SciencesSwedish Research Council, VR 2009-4395 2012-1658Australian Research Council, DP 120104251Wenner-Gren Foundations
Available from: 2012-08-31 Created: 2012-08-31 Last updated: 2017-12-07Bibliographically approved
6. Revision of the tommotiid Kulparina rostrata  (Conway Morris & Bengtson in Bengtson et al. 1990) from South Australia
Open this publication in new window or tab >>Revision of the tommotiid Kulparina rostrata  (Conway Morris & Bengtson in Bengtson et al. 1990) from South Australia
(English)Manuscript (preprint) (Other academic)
Keyword
Tommotiid, Kulparina, Eccentrotheca, sclerite, scleritome, lower Cambrian, South Australia
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-180193 (URN)
Available from: 2012-08-31 Created: 2012-08-31 Last updated: 2013-01-23

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