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Skovsted, Christian B.
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Publications (10 of 16) Show all publications
Skovsted, C. B., Brock, G. A. & Topper, T. P. (2012). First occurrence of a new Ocruranus-like helcionelloid mollusc from the lower Cambrian of East Gondwana. Gondwana Research, 22(1), 256-261
Open this publication in new window or tab >>First occurrence of a new Ocruranus-like helcionelloid mollusc from the lower Cambrian of East Gondwana
2012 (English)In: Gondwana Research, ISSN 1342-937X, E-ISSN 1878-0571, Vol. 22, no 1, p. 256-261Article in journal (Refereed) Published
Abstract [en]

A new cap-shaped mollusc, Emargimantus angulatus gen. et sp. nov. is described from the Arrowie Basin of South Australia. The new species is closely comparable to mollusc species from South China and North-East Greenland previously described under the generic name Ocruranus Liu, a genus recently reinterpreted as a multiplated, possibly polyplacophoran mollusc. Emargimantus is interpreted as a univalved helcionelloid mollusc and differs from Ocruranus in both morphology and function. E. angulatus represents the first discovery of Ocruranus-like helcionelloids in the lower Cambrian of eastern Gondwana and demonstrates that these molluscs had a global distribution during the early Cambrian.

Keywords
Emargimantus, Helcionelloida, Ocruranus, Lower Cambrian, Gondwana
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-178545 (URN)10.1016/j.gr.2011.09.003 (DOI)000305106800019 ()
Available from: 2012-08-01 Created: 2012-07-31 Last updated: 2017-12-07Bibliographically approved
Holmer, L. E., Skovsted, C. B., Larsson, C., 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
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, p. 235-239Article 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.

Keywords
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
Topper, T. P., Brock, G. A., Skovsted, C. B. & Paterson, J. R. (2011). Microdictyon plates from the lower Cambrian Ajax Limestone of South Australia: Implications for species taxonomy and diversity. Alcheringa, 35(3), 427-443
Open this publication in new window or tab >>Microdictyon plates from the lower Cambrian Ajax Limestone of South Australia: Implications for species taxonomy and diversity
2011 (English)In: Alcheringa, ISSN 0311-5518, E-ISSN 1752-0754, Vol. 35, no 3, p. 427-443Article in journal (Refereed) Published
Abstract [en]

A small assemblage of isolated Microdictyon plates is described from the lower Cambrian Ajax Limestone, Mt Scott Range (Flinders Ranges), South Australia. Microdictyon plates are primarily known from single, isolated, perforated phosphatic sclerites; only one species (M. sinicum) from the Chengjiang Lagerstatte is known from soft-bodied preservation of the complete organism. The isolated plates from South Australia display a wide range of morphologies potentially reflecting: 1, considerable diversification within the group at this time; 2, extensive intraspecific morphological variation; 3, different plate morphotypes along the trunk of the animal; or 4, significant ontogenetic variation in successive growth stages. The South Australian specimens are similar to several individual sclerites described from other Cambrian palaeocontinents, but appear closest to faunas described from South China. Problems associated with the taxonomy of isolated Microdictyon plates are discussed, including the lack of knowledge associated with intraspecific and/or ontogenetic variability and how individual plate morphology may relate to size or relative position along the length of the complete organism.

Keywords
stem group lobopodians, small shelly fossils, sclerites, Ajax Limestone, Flinders Ranges, Gondwana
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-172196 (URN)10.1080/03115518.2011.533972 (DOI)000299422600009 ()
Available from: 2012-04-03 Created: 2012-04-02 Last updated: 2017-12-07Bibliographically approved
Skovsted, C. B., Brock, G. A., Topper, T. P., Paterson, J. R. & Holmer, L. E. (2011). Scleritome construction, biofacies, biostratigraphy and systematics of the tommotiid Eccentrotheca helenia sp. nov. from the Early Cambrian of South Australia. Palaeontology, 54, 253-286
Open this publication in new window or tab >>Scleritome construction, biofacies, biostratigraphy and systematics of the tommotiid Eccentrotheca helenia sp. nov. from the Early Cambrian of South Australia
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2011 (English)In: Palaeontology, ISSN 0031-0239, E-ISSN 1475-4983, Vol. 54, p. 253-286Article in journal (Refereed) Published
Abstract [en]

Large collections of Eccentrotheca helenia sp. nov. from the lower Cambrian Wilkawillina and Ajax limestones in the Arrowie Basin, South Australia, contain abundant low, cap-shaped and high, laterally compressed isolated sclerites in addition to partially articulated tubular specimens. The scleritome of Eccentrotheca helenia sp. nov. is fully described for the first time and shown to be formed by ontogenetic fusion of sclerites into successively stacked sclerite rings, forming a larger, tubular structure. The apical termination of the tube is highly variable, but is primarily constructed by low, cap-shaped sclerites and characterised by a central aperture of variable inclination. The adapical portion of the tube is predominantly constructed by high, laterally compressed sclerites, but individual sclerite rings can contain both cap-shaped and laterally compressed sclerites along with sclerites of intermediate morphology. The apical aperture presumably housed organic structures for attachment to a hard substrate, but the scleritome also occasionally preserves small lateral perforations between fused sclerites, which may have served to stabilise the scleritome by providing additional points of anchorage. In the Arrowie Basin, E. helenia is found in association with archaeocyath-microbial-spongiomorph-dominated bioherms and most likely inhabited pendant or cryptic habitats within these bioherms. Eccentrotheca-like sclerites form an integral part of the scleritomes of many tommotiids which may confuse taxonomic analysis. Sclerites previously assigned to 'E.' guano, consistently occur together with sclerites of Kulparina rostrata in stratigraphic intervals consistently older than strata hosting E. helenia. Rare fused specimens indicate that the sclerites of K. rostrata and 'E.' guano belong to the same scleritome.

Keywords
Tommotiida, Brachiopoda, Kulparina, sclerite morphology, scleritome structure, ontogeny, ecology
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-150725 (URN)10.1111/j.1475-4983.2010.01031.x (DOI)000288448800003 ()
Available from: 2011-04-05 Created: 2011-04-05 Last updated: 2017-12-11Bibliographically approved
Skovsted, C. B., Brock, A., Holmer, L. . & Paterson, R. (2009). First report of the early Cambrian stem group brachiopod Mickwitzia from East Gondwana. Gondwana Research, 16(1), 145-150
Open this publication in new window or tab >>First report of the early Cambrian stem group brachiopod Mickwitzia from East Gondwana
2009 (English)In: Gondwana Research, ISSN 1342-937X, E-ISSN 1878-0571, Vol. 16, no 1, p. 145-150Article in journal (Refereed) Published
Abstract [en]

The first mickwitziid brachiopod, Mickwitzia sp.. from East Gondwana is described from the lower Cambrian Ajax Limestone, Mt Scott Range in South Australia. The shells are fragmentary, but preserve sufficient details of morphology and micro-structure to allow positive identification to genus. The morphology of the dorsal valve apex and the extended cones on the internal surface indicate a close affinity with Mickwitzia muralensis Walcott, 1913 from the early Cambrian of British Columbia, but Scarcity of material precludes detailed comparison. This find extends the known range of the pivotal stem group brachiopod Mickwitzia to East Gondwana. (C) 2009 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Keywords
Mickwitzia, Brachiopoda, South Australia, Lower Cambrian, Biogeography
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-128344 (URN)10.1016/j.gr.2009.02.002 (DOI)000268270100012 ()
Available from: 2010-07-22 Created: 2010-07-20 Last updated: 2017-12-12Bibliographically approved
Balthasar, U., Skovsted, C. B., Holmer, L. E. & Brock, A. (2009). Homologous skeletal secretion in tommotiids and brachiopods. Geology, 37(12), 1143-1146
Open this publication in new window or tab >>Homologous skeletal secretion in tommotiids and brachiopods
2009 (English)In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 37, no 12, p. 1143-1146Article in journal (Refereed) Published
Abstract [en]

Tommotiids are distinctive components of the early Cambrian small shelly fauna, almost invariably represented by isolated phosphatic sclerites derived from a multielement protective cover (scleritome). The unusual range of tommotiid sclerite morphologies and unknown construction of the scleritome have severely hampered our understanding of their phylogenetic affinities. However, recent description of rare, articulated scleritome material belonging to the tommotiid genera Eccentrotheca and Paterimitra support the hypothesis that some tommotiids fall within the stem group of the lophophorate phyla Phoronida and Brachiopoda and that at least some tommotiid sclerites are homologous precursors of the shells of organophosphatic brachiopods. Here we show that the shell microstructure of Eccentrotheca and Paterimitra share substantial similarities with paterinid brachiopods. While paterinids possess an overall brachiopod morphology, their microstructure appears more similar to Eccentrotheca and Paterimitra than to nonpaterinate lingulids. These findings strongly support the existence of a brachiopod total group that is solidly rooted within tommotiids, and identify the organophosphatic skeletal composition as plesiomorphic with calcareous shells as derived. The microstructural changes of the proposed tommotiid-brachiopod transition probably reflect an adaptation to fluctuating food and phosphorous intake that came with the switch to a sessile life style at the base of the tommotiid clade.

National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-127391 (URN)10.1130/G30323A.1 (DOI)000272353200022 ()
Available from: 2010-07-13 Created: 2010-07-13 Last updated: 2017-12-12Bibliographically approved
Holmer, L. E., Pettersson Stolk, S., Skovsted, C. B., Balthasar, U. & Popov, L. (2009). The enigmatic early cambrian salanygolina: a stem group of rhynchonelliform chileate brachiopods?. Palaeontology, 52(1), 1-10
Open this publication in new window or tab >>The enigmatic early cambrian salanygolina: a stem group of rhynchonelliform chileate brachiopods?
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2009 (English)In: Palaeontology, ISSN 0031-0239, E-ISSN 1475-4983, Vol. 52, no 1, p. 1-10Article in journal (Refereed) Published
Abstract [en]

New material of the enigmatic brachiopod Salanygolina obliqua Ushatinskaya from the Early Cambrian of Mongolia shows that it has a colleplax- a triangular plate - in the umbonal perforation, which is enlarged by resorption. This structure is otherwise only known from the equally enigmatic Palaeozoic orders Chileida and Dictyonellida (Rhynchonelliformea, Chileata). The colleplax in Salanygolina is here considered to be homologous with that of the chileates. Salanygolina is also provided with a ridge-like pseudodeltidium, which is another chileate feature. Other characters of Salanygolina, like the radial arrangement of adductor muscle scars and postero-medially placed internal oblique muscles are characteristic of chileates, but also found in the paterinates. In contrast, mixoperipheral dorsal valves with low rudimentary interareas are well known in paterinates, but not yet recorded from chileates. Thus, Salanygolina shows a mosaic combination of morphologic characters, known both from the paterinates and chileates, indicating that it may represent a stem group of the rhynchonelliform chileate brachiopods. The laminar phosphatic secondary shell of Salanygolina is composed of closely packed and nearly identical hexagonal prisms, oriented with their long axis normal to the laminae in a honeycomb pattern. The prism walls appear to have originally been composed of organic membranes and might represent precursors of the organic sheaths of calcite fibers that are typical of calcitic shells with a fibrous microstructure.

Keywords
Brachiopoda, Family Salanygolinidae, Salanygolina, Early Cambrian, Mongolia
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-129259 (URN)10.1111/j.1475-4983.2008.00831.x (DOI)000262131100001 ()
Available from: 2010-08-10 Created: 2010-08-10 Last updated: 2017-12-12Bibliographically approved
Skovsted, C. B., Holmer, L. E., Larsson, C. M., Högström, A. E. S., Brock, G. A., Topper, T. P., . . . Paterson, J. R. (2009). The scleritome of Paterimitra: an Early Cambrian stem group brachiopod from South Australia. Proceedings of the Royal Society of London. Biological Sciences, 276(1662), 1651-1656
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, p. 1651-1656Article 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
Skovsted, C. B., Brock, G. A., Paterson, J. R., Holmer, L. E. & Budd, G. E. (2008). The scleritome of Eccentrotheca from the Lower Cambrian of South Australia: Lophophorate affinities and implications for tommotiid phylogeny. Geology, 36(2), 171-174
Open this publication in new window or tab >>The scleritome of Eccentrotheca from the Lower Cambrian of South Australia: Lophophorate affinities and implications for tommotiid phylogeny
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2008 (English)In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 36, no 2, p. 171-174Article in journal (Refereed) Published
Abstract [en]

The first partially articulated scleritome of a tommotiid, Eccentrotheca sp., is described from the Lower Cambrian of South Australia. The Eccentrotheca scleritome consists of individual sclerites; fused in a spiral arrangement, forming a tapering tube-shaped skeleton with an inclined apical aperture and a circular to subcircular cross section. Traditionally, tommotiid sclerites have been assumed to form a dorsal armor of imbricating phosphatic plates in slug-like bilaterians, analogous to the calcareous sclerites of halkieriids. The structure of the Eceentrotheca scleritome is here reinterpreted as a tube composed of independent, irregularly shaped sclerites growing by basal-marginal accretion that were successively fused to form a rigid, protective tubular structure. The asymmetrical shape and sometimes acute inclination of the apical aperture suggests that the apical part of the scleritome was cemented to a hard surface via a basal disc, from which it projected vertically. Rather than being a vagrant member of the benthos, Eccentrotheca most likely represented a sessile, vermiform filter feeder. The new data suggest that the affinities of Eccentrotheca, and possibly some other problematic tommotiids, lie with the lophophorates (i.e., the phoronids and brachiopods), a clade that also possesses a phosphatic shell chemistry and a sessile life habit.

Keywords
tommotiida, phylogeny, Brachiopoda, Phoronida, Lower Cambrian
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-17769 (URN)10.1130/G24385A.1 (DOI)000252829600019 ()
Available from: 2008-08-26 Created: 2008-08-26 Last updated: 2017-12-08Bibliographically approved
Skovsted, C., Brock, G. A., Paterson, J. R., Holmer, L. & Budd, G. (2007). Eccentrotheca from the Lower Cambrian of South Australia – the first known tommotiid scleritome and its biological implications. In: 51st Palaeontological Association Annual Meeting: Programme with Abstracts (pp. 55).
Open this publication in new window or tab >>Eccentrotheca from the Lower Cambrian of South Australia – the first known tommotiid scleritome and its biological implications
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2007 (English)In: 51st Palaeontological Association Annual Meeting: Programme with Abstracts, 2007, p. 55-Conference paper, Published paper (Other scientific)
Abstract [en]

The discovery of the first partially articulated scleritome of a tommotiid, Eccentrotheca sp. from the Lower Cambrian of the Flinders Ranges in South Australia necessitates a complete revision of the gross morphology and biological function of the problematic tommotiids. The scleritome of Eccentrotheca is an expanding tubular structure with a circular cross-section that was formed by the episodic merging of individual cone-shaped sclerites. The basal region of the tube has an open aperture, the morphology and inclination of which varies considerably. Growth patterns in the apical region indicate that the aperture housed structures that helped anchor the tube to a hard substrate. The Eccentrotheca animal is consequently reinterpreted as a sessile, epibiotic filter-feeder. This model contrasts sharply to all previously published models of tommotiid animals, which almost without exception envisages a slug-like animal with a dorsal cover of imbricating sclerites (modelled after the scleritome of the coeval halkieriid animal). Tommotiids have been suggested to fall within the stem group of the Brachiopoda, mainly based on the organophosphatic composition and brachiopod-like shell structure of some tommotiids. The sessile, filter-feeding lifestyle inferred from the scleritome of Eccentrotheca appears to strengthen the lophophorate hypothesis of tommotiid relationships, although the tubicous habit of the scleritome is more reminiscent of phoronids than brachiopods.

Identifiers
urn:nbn:se:uu:diva-12600 (URN)
Available from: 2008-01-08 Created: 2008-01-08 Last updated: 2017-01-25
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