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Christian B. Skovsted - One of the best experts on this subject based on the ideXlab platform.
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New early Cambrian Sclerites of Lapworthella schodakensis from NE Greenland: advancements in knowledge of lapworthellid taxonomy, Sclerite growth and scleritome organization
Geological Magazine, 2016Co-Authors: Lea Devaere, Christian B. SkovstedAbstract:The Cambrian Stage 4 upper Bastion Formation of Albert Heim Bjerge and CH Ostenfeld Nunatak, NE Greenland, yielded 34 excellently preserved Sclerites of Lapworthella schodackensis among other small shelly fossils. Lapworthellids have been interpreted as members of the camenellans, a basal tommotiid group. Little is known about this group although the morphological and ultrastructural features of their Sclerites allow a potential reconstruction of a lophophorate body plan. The exquisite material from Greenland provides significant new data for the revision of the species taxonomy, but also for the comprehension of the scleritome structure of lapworthellids and the mode of formation of their Sclerites. Two morphotypes of L. schodackensis Sclerites are identified: one with a simple apex, occurring in sinistral and dextral forms; and one bilaterally symmetrical Sclerite with two apices. All bear a similar ornamentation constructed of repeated growth sets consisting of a reticulate inter-rib groove with tubercles, a densely denticulate rib and a striated sub-rib area. The new data on the ornamentation and observations of the laminar shell microstructure of L. schodackensis enable us to improve the reconstruction of growth in lapworthellids. Finally, the morphological features of the two types of Sclerites provide new information for the reconstruction of the bilaterally symmetrical multi-component lapworthellid scleritome with evidence of the fusion of adjacent Sclerites during early ontogeny.
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tommotiids from the early cambrian series 2 stage 3 of morocco and the evolution of the tannuolinid scleritome and setigerous shell structures in stem group brachiopods
Palaeontology, 2014Co-Authors: Christian B. Skovsted, Sebastien Clausen, Javier J Alvaro, Deborah PonleveAbstract:An assemblage of tannuolinid Sclerites is described from the Amouslek Formation (Souss Basin) of the Anti-Atlas Mountains in Morocco. The assemblage contains two species, Tannuolina maroccana n. sp., which is repre- sented by a small number of mitral and sellate Sclerites, and Micrina sp., represented by a single mitral Sclerite. Tannuoli- na maroccana differs from other species of the genus in the presence of both bilaterally symmetrical and strongly asym- metrical sellate Sclerites. This observation suggests that the scleritome of Tannuolina was more complex than previously thought and that this tommotiid may have held a more basal position in the brachiopod stem group than previously assumed. The shell structure of both T. maroccana and Micrina sp. is well preserved and exhibits two fundamentally different sets of tubular structures, only one of which was likely to contain shell-penetrating setae. Based on these obser- vations, the structure of the tannuolinid shell is discussed and its implications for the evolution of tubular microstructures in stem and crown group brachiopods are analysed.
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Sclerite fusion in the problematic early Cambrian spine-like fossil Stoibostrombus from South Australia
Bulletin of Geosciences, 2011Co-Authors: Christian B. Skovsted, Glenn A. Brock, Timothy P TopperAbstract:New collections of the problematic spine like fossil Stoibostrombus crenulatus Conway Morris & Bengtson from the Mt. Scott Range and Wilkawillina Gorge in the central Flinders Ranges, South Australia contain fused Sclerite composites. In each fused specimen the spines are merged along their lateral margins and the orientation of the spines is almost identical. These new specimens confirm that Stoibostrombus spines were dermal Sclerites, arranged in lateral pairs or transverse rows. The nature of the animal secreting the spines remains elusive, but available evidence suggest that it was an ecdysozoan animal, possibly a palaeoscolecid worm.
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Homologous skeletal secretion in tommotiids and brachiopods
Geology, 2009Co-Authors: Uwe Balthasar, Lars E Holmer, Christian B. Skovsted, Glenn A. BrockAbstract: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.
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the scleritome of paterimitra an early cambrian stem group brachiopod from south australia
Proceedings of The Royal Society B: Biological Sciences, 2009Co-Authors: Christian B. Skovsted, Lars E Holmer, Glenn A. Brock, Uwe Balthasar, Cecilia M Larsson, Anette E S Hogstrom, Timothy P Topper, Sandra Petterson Stolk, John R PatersonAbstract: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.
Glenn A. Brock - One of the best experts on this subject based on the ideXlab platform.
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Chancelloriid Sclerites from the lowermost Cambrian of North China and discussion of Sclerite taxonomy
Geobios, 2019Co-Authors: Hao Yun, Xingliang Zhang, Bing Pan, Glenn A. BrockAbstract:Abstract Chancelloriid Sclerites from the lowermost Cambrian Xinji Formation (Series 2, Stage 3), southern margin of the North China platform, are systematically described. Thousands of isolated Sclerites from three sections are assigned to three genera and four species, including Chancelloria cf. eros, Allonnia tripodophora, Archiasterella pentactina, and Ar. tetraspina. To accurately document the taxonomic significance of the Sclerite structure, modified formulas (m+nC, m+nA, and m+0) are put forward to represent the full series and variation of Sclerite forms. Based on the Sclerite construction, statistical analysis on the proportions of different Sclerite forms in the rock samples and the composition of Sclerites in previously described chancelloriid scleritomes, a new scheme for identification and classification of isolated Sclerites reconciled within the framework of the complete scleritome, is proposed.
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Sclerite fusion in the problematic early Cambrian spine-like fossil Stoibostrombus from South Australia
Bulletin of Geosciences, 2011Co-Authors: Christian B. Skovsted, Glenn A. Brock, Timothy P TopperAbstract:New collections of the problematic spine like fossil Stoibostrombus crenulatus Conway Morris & Bengtson from the Mt. Scott Range and Wilkawillina Gorge in the central Flinders Ranges, South Australia contain fused Sclerite composites. In each fused specimen the spines are merged along their lateral margins and the orientation of the spines is almost identical. These new specimens confirm that Stoibostrombus spines were dermal Sclerites, arranged in lateral pairs or transverse rows. The nature of the animal secreting the spines remains elusive, but available evidence suggest that it was an ecdysozoan animal, possibly a palaeoscolecid worm.
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Homologous skeletal secretion in tommotiids and brachiopods
Geology, 2009Co-Authors: Uwe Balthasar, Lars E Holmer, Christian B. Skovsted, Glenn A. BrockAbstract: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.
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the scleritome of paterimitra an early cambrian stem group brachiopod from south australia
Proceedings of The Royal Society B: Biological Sciences, 2009Co-Authors: Christian B. Skovsted, Lars E Holmer, Glenn A. Brock, Uwe Balthasar, Cecilia M Larsson, Anette E S Hogstrom, Timothy P Topper, Sandra Petterson Stolk, John R PatersonAbstract: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.
Lars E Holmer - One of the best experts on this subject based on the ideXlab platform.
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Homologous skeletal secretion in tommotiids and brachiopods
Geology, 2009Co-Authors: Uwe Balthasar, Lars E Holmer, Christian B. Skovsted, Glenn A. BrockAbstract: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.
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the scleritome of paterimitra an early cambrian stem group brachiopod from south australia
Proceedings of The Royal Society B: Biological Sciences, 2009Co-Authors: Christian B. Skovsted, Lars E Holmer, Glenn A. Brock, Uwe Balthasar, Cecilia M Larsson, Anette E S Hogstrom, Timothy P Topper, Sandra Petterson Stolk, John R PatersonAbstract: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.
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Shell structure and inferred growth, functions and affinities of the Sclerites of the problematic Micrina
Palaeontology, 2002Co-Authors: Alwyn Williams, Lars E HolmerAbstract:The stratiform laminae of Micrina Sclerites originally consisted of rheomorphic successions of monolayers of micrometric–sized, apatitic tablets, presumably interleaved with chitin and glycosaminoglycans (GAGs). Paired laminae enclose slot–like chambers swelling into lobes distally that originally contained GAGs and deposits of spherulitic and prismatic apatite. The laminae are pervaded by apatitic tubes, apparently secreted by microvillous setoblasts and containing, at the surface, chitinous setae. Internal markings suggest that the triangular (sellate) Sclerite supported a pair of muscles and the planospiral (mitral) Sclerite, a medial muscle and gonadal sacs flanked by a pair of crescentic muscle bases. Both Sclerites were secreted by a mantle with a circumferential fold. The sellate and mitral Sclerites are homologized with the anterior and posterior shells of Halkieria and could have become the dorsal and ventral valves of the ancestral brachiopod by a sequence of transformations. These include: the folding of the halkieriid body axis; accelerated mixoperipheral growth of the anterior (dorsal) shell to enclose, with the posterior (ventral) shell, a mantle cavity lined with modified ciliated epithelium of the foot; reduction of Sclerite–secreting epithelium to the locus of the brachiopod pedicle epithelium; and the anterior (dorsal) spread of gonadal lamellae.
Uwe Balthasar - One of the best experts on this subject based on the ideXlab platform.
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Homologous skeletal secretion in tommotiids and brachiopods
Geology, 2009Co-Authors: Uwe Balthasar, Lars E Holmer, Christian B. Skovsted, Glenn A. BrockAbstract: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.
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the scleritome of paterimitra an early cambrian stem group brachiopod from south australia
Proceedings of The Royal Society B: Biological Sciences, 2009Co-Authors: Christian B. Skovsted, Lars E Holmer, Glenn A. Brock, Uwe Balthasar, Cecilia M Larsson, Anette E S Hogstrom, Timothy P Topper, Sandra Petterson Stolk, John R PatersonAbstract: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.
John R Paterson - One of the best experts on this subject based on the ideXlab platform.
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the scleritome of paterimitra an early cambrian stem group brachiopod from south australia
Proceedings of The Royal Society B: Biological Sciences, 2009Co-Authors: Christian B. Skovsted, Lars E Holmer, Glenn A. Brock, Uwe Balthasar, Cecilia M Larsson, Anette E S Hogstrom, Timothy P Topper, Sandra Petterson Stolk, John R PatersonAbstract: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.
