| 1. |
- Balthasar, Uwe
(författare)
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An Early Cambrian organophosphatic brachiopod with calcitic granules
- 2007
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Ingår i: Palaeontology. - : Wiley. - 0031-0239 .- 1475-4983. ; 50:6, s. 1319-1325
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Tidskriftsartikel (refereegranskat)abstract
- The linguliform brachiopod Eoobolus from the Early Cambrian Mural Formation (Jasper National Park, Canadian Rocky Mountains) exhibits various calcitic features in its otherwise apatitic shell. It is argued here that the decomposition of the organic matter within the shell led to a microenvironment similar to those resulting in the phosphatization of soft tissues. This diagenetic regime encouraged the initial precipitation of apatite cements followed by calcite cements. By fully coating primary structures early apatite cements separate primary structures from the later precipitation of calcite cement. Round calcareous grains, about 3 µm in size, that occur in the centre of apatite botryoids must therefore represent original components of the shell. The equivalent pits of such calcareous granules are seen in the larval shells of many Palaeozoic linguliform brachiopods. This suggests that mixed organophosphatic-calcareous shells were relatively common at that time but that they have been overlooked owing to the obliteration of original calcareous structures by traditional acid preparation methods for the extraction of phosphatic fossils. The Eoobolus shell structure is intermediate between purely organophosphatic and calcitic shells. Although one such genus is not sufficient to reconstruct the ancestral composition of the brachiopod shell, it provides a means of recognizing other transitional forms that are needed to understand fully the shift in shell mineralogy.
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| 2. |
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| 3. |
- Balthasar, Uwe, et al.
(författare)
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Early Cambrian "soft-shelled" brachiopods as possible stem-group phoronids
- 2009
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Ingår i: Acta Palaeontologica Polonica. - 0567-7920 .- 1732-2421. ; 54:2, s. 307-314
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Tidskriftsartikel (refereegranskat)abstract
- Brachiopods and phoronids are widely recognised as closely related lophophorate phyla. but the lack of morphological intermediates linking the bivalved bodyplan of brachiopods with tubular phoronids has frustrated precise phylogenetic placement. Here we describe Lingulosacculus nuda gen. et sp. nov., a new "soft-shelled" brachiopod from the Early Cambrian Mural Formation of western Alberta which provides a plausible candidate for a phoronid stem-group within (paraphyletic) Brachiopoda. In addition to its non-biomineralised shell, L. nuda had a ventral valve with an exceptionally long, pocket-like extension (pseudointerarea) that Would have allowed the transformation of criss-crossing brachiopod-type musculature to the longitudinal arrangement typical of phoronids. "Soft-shelled" linguliform brachiopods have previously been reported from both the Chengjiang and Burgess Shale Lagerstatten which, together with L. nuda. probably represent two independent losses of shell mineralisation in brachiopods.
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| 4. |
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| 5. |
- Balthasar, Uwe, et al.
(författare)
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Homologous skeletal secretion in tommotiids and brachiopods
- 2009
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Ingår i: Geology. - 0091-7613 .- 1943-2682. ; 37:12, s. 1143-1146
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Tidskriftsartikel (refereegranskat)abstract
- 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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| 6. |
- Balthasar, Uwe
(författare)
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Mummpikia gen. nov and the origin of calcitic-shelled brachiopods
- 2008
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Ingår i: Palaeontology. - : Wiley. - 0031-0239 .- 1475-4983. ; 51:2, s. 263-279
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Tidskriftsartikel (refereegranskat)abstract
- Phosphatised limestone-hosted and shale-hosted specimens of the obolellid Mummpikia nuda gen. et comb. nov. and two further unidentified obolellids from the Early Cambrian Mural Formation (jasper National Park, Canadian Rocky Mountains) provide novel insights into the shell microstructure of obolellids and the nature of their pedicle. The shell was penetrated by abundant canals of a sub-pm diameter and the anterior tip of the delthyrium forms a projection into the body cavity that is penetrated by a thin canal. It is argued that both shell microstructure and posterior margin are linguliformean characters and that obolellids hold a position basal in the rhynchonelliform stem-group.
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| 7. |
- Balthasar, Uwe
(författare)
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The brachiopod Eoobolus from the Early Cambrian Mural Formation (Canadian Rocky Mountains)
- 2009
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Ingår i: Palaeontologische Zeitschrift. - : Springer Science and Business Media LLC. - 0031-0220 .- 1867-6812. ; 83:3, s. 407-418
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Tidskriftsartikel (refereegranskat)abstract
- The Early Cambrian brachiopod, Eoobolus, is one of the first representatives of the superfamily, Linguloidea, the defining characteristics of which include the classical morphology of oval shells and a pedicle that emerges from between the two valves. The material described here from the Mural Formation (Jasper National Park, Canadian Rocky Mountains) provides well-preserved muscle scars and larval shells that allow a discussion of the muscle system and the larval morphology of Eoobolus. The dorsal larval shell exhibits a morphology similar to other Cambrian linguloids, but also to paterinids, Mickwitzia muralensis, and some rhynchonelliforms. This suggests that there was a lesser degree of disparity among brachiopod larvae in the Cambrian than there is today. The muscle system of Eoobolus is similar to other linguloids, but differs from that of Recent lingulids and discinids by having one or two more pairs of oblique muscles. New data on the distribution of features characteristic of the family Eoobolidae question the validity of this family.
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| 8. |
- Butterfield, N.J., et al.
(författare)
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Fossil diagenesis in the Burgess Shale
- 2007
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Ingår i: Palaeontology. - : Wiley. - 0031-0239 .- 1475-4983. ; 50:3, s. 537-543
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Tidskriftsartikel (refereegranskat)abstract
- Current models for the exceptional preservation of Burgess Shale fossils have focused on either the HF-extractable carbonaceous compressions or the mineral films identified by elemental mapping. BSEM, EDX and microprobe analysis of two-dimensionally preserved Marpolia, Wiwaxia and Burgessia identifies the presence of both carbonaceous and aluminosilicate films for most features, irrespective of original lability. In the light of the deep burial and greenschist facies metamorphism documented for the Burgess Shale, the aluminosilicate films are identified as products of late-stage volatilization and coincident mineralization of pre-existing compression fossils, whereas the three-dimensionally preserved gut-caecal system of Burgessia is interpreted as an aluminosilicate replacement of a pre-existing carbonate phase. The case for late diagenetic emplacement of aluminosilicate minerals is supported by the extensive aluminosilicification of trilobite shell and (originally) calcareous veinlets in the Burgess Shale, as well as documentation of other secondarily aluminosilicified compression fossils. By distinguishing late diagenetic alteration from the early diagenetic processes responsible for exceptional preservation, it is possible to reconcile the range of preservational modes currently expressed in the Burgess Shale.
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| 9. |
- Grazhdankin, Dmitriy V., et al.
(författare)
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Carbonate-hosted Avalon-type fossils in arctic Siberia
- 2008
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Ingår i: Geology. - 0091-7613 .- 1943-2682. ; 36:10, s. 803-806
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Tidskriftsartikel (refereegranskat)abstract
- Avalon-type fossils are crucial to understanding the origin of Phanerozoic ecosystems, but their usual occurrence in volcaniclastic and siliciclastic facies greatly limits their paleobiological resolution. The unique carbonate-hosted. assemblage of the Khatyspyt Formation, on the Olenek uplift of north-central Siberia, promises a much enhanced anatomical and paleoecological view of these enigmatic organisms. Avalon-type fossils are preserved by authigenic carbonate cementation in intervals of finely laminated nodular limestones (Khatyspyt-type taphonomic window). Interbedded silicified calcareous mudstones yield diverse carbonaceous compressions, occasionafly with taphonomic phantoms of Avalon-type taxa (Miaohetype taphonomic window). Styles of moldic preservation do not appear to be taxon selective, and therefore cannot alone be responsible for the morphological distinctiveness of Ediacaran macrofossils and the profound disparity in the taxonomic composition between fossil assemblages. On the other hand, the exclusion of Avalon-type fossils from carbonaceous compressions (Miaohe-type preservational window) is a real taphonomic signal that provides an important constraint on the properties of certain Ediacaran tissues.
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| 10. |
- Holmer, Lars E., et al.
(författare)
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The enigmatic early cambrian salanygolina : a stem group of rhynchonelliform chileate brachiopods?
- 2009
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Ingår i: Palaeontology. - : Wiley. - 0031-0239 .- 1475-4983. ; 52:1, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 11. |
- Knight, Ian
(författare)
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The Lower Cambrian Forteau Formation, southern Labrador and Great Northern Peninsula, western Newfoundland: Lithostratigraphy, trilobites, and depositional setting.
- 2017
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The upper Lower Cambrian Forteau Formation in southern Labrador and the Great Northern Peninsula (GNP) is a successionof shale, limestone, siltstone and sandstone accommodated by rising sea levels during the early drift stages ofNewfoundland’s Laurentian passive margin. Its Dyeran trilobite fauna, characterized by Elliptocephala logani (Walcott, 1910)that ranges throughout the formation, indicates it was mostly deposited in the middle Bonnia‒Olenellus Zone. Its three lithostratigraphicdivisions, the Devils Cove member, Middle shale and Upper limestone, preserve a transgressive system tract(TST; Devils Cove and lower part of the Middle shale) and the early stages of a regressive high-stand system tract (HST; upper Middle shale and Upper limestone) that hosts a carbonate ramp shelf.A mudstone-dominated succession characterizes the TST, comprised of an inner belt of archeocyathid patch reef andcyclic, well-stratified, fine-grained mixed clastic and carbonate shelf rocks in southern Labrador. To the southeast on the GNP,the shale succession along with minor limestone and no reefs suggests a deeper water shelf basin in which shale accumulated across the GNP. Maximum flooding on the GNP is linked to dark shale midway through the basinal succession, and to athick shale bed that overlies the reefal strata in Labrador.Thin-bedded siltstone, sandstone and limestone in Labrador, and extensively bioturbated siltstone, sandstone and rare limestone on the GNP, support a shelf shallowing above storm-wave base as it prograded during the early stages of regression. Shallow-water carbonate of the Upper limestone supports a prograding shelf, at first dominated by an archeocyathid reefal tract and oolitic shoal complex. The reef tract and carbonate sand shoal complex prograded southeastward to justbeyond the northeast-trending Ten Mile Lake–Long Range fault system. Evidence of slumping in the underlying fine clastic sediment in the same area suggest that this fault zone may coincide with a hinge zone, beyond which the shelf steepened intomostly deep-water clastic sedimentation. The archeocyathid tract in southern Labrador is a broad biostromal complex confined within an erosional recess in the shelf. On the GNP, however, the tract is characterized by high-energy bioherms associated with crossbedded grainstone channels that can be traced for over 60 km along a northeast strike length. East of the reef tract‒shoal complex, the succession appears to be dominated by deeper water shelf mudrock, nodular carbonate and little evidence of shallow-water carbonate facies. The facies transition suggests the Forteau Formation insouthern Labrador and the GNP was laid down in a high-energy shallow-water, inner ramp setting that was up to 75 km wide. Above the carbonate sand shoal complex, the succession is marked by decametre-thick parasequences of intercalated carbonateand clastic intervals. The sequences support a shelf of fine grained to grainy carbonate deposited on an open shelframp overlain by intervals dominated by coarsening upward high-energy siliciclastics that suggest barrier complexes alongthe landward margin of the ramp. Thick units of crossbedded quartz arenite, in the upper half of the Upper limestone, suggest terrigenous sediments initially encroached along the inner part of the shelf, and eventually smothered the Forteau shelf leading to the low-stand deposits of the overlying Hawke Bay Formation. Trilobites recovered from this transition throughout the GNP, indicate that it occurred very late in the upper part of the Bonnia‒Olenellus Zone, likely between the Bristolia mohavensis Biozone and the top of the zone.
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| 12. |
- Larsson, Cecilia M., et al.
(författare)
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Paterimitra pyramidalis from South Australia : Scleritome, shell structure and evolution of a lower Cambrian stem group brachiopod
- 2014
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Ingår i: Palaeontology. - : Wiley. - 0031-0239 .- 1475-4983. ; 57:2, s. 417-446
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 13. |
- Skovsted, Christian B., et al.
(författare)
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The scleritome of Paterimitra : an Early Cambrian stem group brachiopod from South Australia
- 2009
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Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 276:1662, s. 1651-1656
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Tidskriftsartikel (refereegranskat)abstract
- 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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| 14. |
- Skovsted, Christian B., et al.
(författare)
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The tommotiid Camenella reticulosa from the early Cambrian of South Australia : Morphology, scleritome reconstruction, and phylogeny
- 2009
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Ingår i: Acta Palaeontologica Polonica. - : Polska Akademia Nauk Instytut Paleobiologii (Institute of Paleobiology, Polish Academy of Sciences). - 0567-7920 .- 1732-2421. ; 54:3, s. 525-540
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Tidskriftsartikel (refereegranskat)abstract
- The tommotiid Camenella reticulosa is redescribed based on new collections of well preserved sclerites from the Arrowie Basin (Flinders Ranges), South Australia, revealing new information concerning morphology and microstructure. The acutely pyramidal mitral sclerite is described for the first time and the sellate sclerite is shown to be coiled through up to 1.5 whorls. Based on Camenella, a model is proposed by which tommotiid sclerites are composed of alternating dense phosphatic, and presumably originally organic-rich, laminae. Camenella is morphologically most similar to Lapworthella, Kennardia, and Dailyatia, and these taxa are interpreted to represent a monophyletic clade, here termed the "camenellans", within the Tommotiida. Potential reconstructions of the scleritome of Camenella are discussed and although a tubular scleritome construction was recently demonstrated for the tommotiids Eccentrotheca and Paterimitra, a bilaterally symmetrical scleritome model with the sclerites arranged symmetrically on the dorsal surface of a vagrant animal can not be ruled out.
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| 15. |
- Skovsted, Christian, 1974-, et al.
(författare)
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Depth related brachiopod faunas from the lower Cambrian Forteau Formation of southern Labrador and western Newfoundland, Canada
- 2017
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Ingår i: Palaeontologia Electronica. - : Coquina Press. - 1935-3952 .- 1094-8074. ; 20:3, s. 1-52
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Tidskriftsartikel (refereegranskat)abstract
- A diverse fauna of organophosphatic brachiopods is described from the late early Cambrian (Series 2, Stage 3-4) Forteau Formation of southern Labrador and western Newfoundland. The total fauna includes 11 species representing a wide selection of Cambrian brachiopod groups. Three distinct assemblages are recognized: Assemblages1 and 2 are found in shallow water carbonates in association with archaeocyathans in southern Labrador and the western side of the Great Northern Peninsula of western Newfoundland. Assemblage 3 is found in a distal shelf setting of Gros Morne National Park. Assemblages 1 and 2 are found in stratigraphic continuity and definetwo brachiopod biozones, a lower Hadrotreta taconica zone and a higher Paterina zone, respectively. The presence of H. taconica in brachiopod Assemblage 3 possibly indicates time equivalence of Assemblage 1 but in a deep water setting. The identification of distinct time equivalent brachiopod Assemblages (1 and 3) in shallow and deep water environments of the Forteau Formation allow for the first time an analysis of environmental constraints determining the distribution of individual brachiopod taxa in the lower Cambrian succession of eastern Laurentia. Comparison to faunas from other areas indicates that the identified distributional patterns can be extended to other brachiopod faunas found along the Cambrian palaeocoast/margin of eastern Laurentia. The study indicates that specific brachiopod taxa can be used as indicators of palaeodepth; Botsfordia caelata in shallow environments and Eoobolus priscus and Eothele tubulus in deeper water. The following new taxa are described: Kyrshabaktella diabolan. sp., Pustulobolus triangulus n. gen et n. sp., Acrothyra bonnia n. sp.
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| 16. |
- Skovsted, Christian, 1974-, et al.
(författare)
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SMALL SHELLY FOSSILS AND CARBON ISOTOPES FROM THE EARLY CAMBRIAN (STAGES 3–4) MURAL FORMATION OF WESTERN LAURENTIA
- 2021
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Ingår i: Papers in Palaeontology. - : Wiley. - 2056-2799 .- 2056-2802. ; 7:2, s. 951-983
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Tidskriftsartikel (refereegranskat)abstract
- The extraordinary window of phosphatized and phosphatic small shelly fossils (SSF) during the early and middle Cambrian is an important testament to the radiation of biomineralizing metazoans. While SSF are well known from most Cambrian palaeocontinents during this time interval, western Laurentia has relatively few SSF faunas. Here we describe a diverse SSF fauna from the early Cambrian (Stages 3–4) Mural Formation at three localities in Alberta and British Columbia, Canada, complemented by carbon isotope measurements to aid in a potential future bio-chemostratigraphic framework. The fauna expands the recorded SSF assemblage diversity in western Laurentia and includes several brachiopods, four bradoriids, three chancelloriids, two hyoliths, a tommotiid and a helcionellid mollusc as well as echinoderm ossicles and specimens of Microdictyon, Volborthella and Hyolithellus. New taxa include the tommotiid genus Canadiella gen. nov., the new bradoriid species Hipponicharion perforata sp. nov. and Pseudobeyrichona taurata sp. nov. Compared with contemporaneous faunas from western Laurentia, the fauna is relatively diverse, particularly in taxa with originally phosphatic shells, which appear to be associated with archaeocyathid build-ups. This suggests that the generally low faunal diversity in western Laurentia may be at least partly a consequence of poor sampling of suitable archaeocyathan reef environments. In addition, the tommotiid Canadiella filigrana appears to be of biostratigraphical significance in Cambrian Stage 3 strata of western Laurentia, and the unexpected high diversity of bradoriid arthropods in the fauna also suggests that this group may prove useful for biostratigraphical resolution in the region.
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| 17. |
- Sperling, Erik Anders, et al.
(författare)
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On the edge of exceptional preservation: insights into the role of redox state in Burgess Shale-type taphonomic windows from the Mural Formation, Alberta, Canada
- 2018
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Ingår i: Emerging Topics In Life Sciences. - 2397-8554 .- 2397-8562. ; 2:2, s. 311-323
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Tidskriftsartikel (refereegranskat)abstract
- Animals originated in the Neoproterozoic and ‘exploded’ into the fossil record in the Cambrian. The Cambrian also represents a high point in the animal fossil record for the preservation of soft tissues that are normally degraded. Specifically, fossils from Burgess Shale-type (BST) preservational windows give paleontologists an unparalleled view into early animal evolution. Why this time interval hosts such exceptional preservation, and why this preservational window declines in the early Paleozoic, have been long-standing questions. Anoxic conditions have been hypothesized to play a role in BST preservation, but recent geochemical investigations of these deposits have reached contradictory results with respect to the redox state of overlying bottom waters. Here, we report a multi-proxy geochemical study of the Lower Cambrian Mural Formation, Alberta, Canada. At the type section, the Mural Formation preserves rare recalcitrant organic tissues in shales that were deposited near storm wave-base (a Tier III deposit; the worst level of soft-tissue preservation). The geochemical signature of this section shows little to no evidence of anoxic conditions, in contrast to published multi-proxy studies of more celebrated Tier I and II deposits. These data help confirm that ‘decay limited’ BST biotas were deposited in more oxygenated conditions, and support a role for anoxic conditions in BST preservation. Finally, we discuss the role of iron reduction in BST preservation, including the formation of iron-rich clays and inducement of sealing seafloor carbonate cements. As oceans and sediment columns became more oxygenated and more sulfidic through the early Paleozoic, these geochemical changes may have helped close the BST taphonomic window.
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| 18. |
- Topper, Timothy P, et al.
(författare)
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The oldest brachiopods from the lower Cambrian of South Australia
- 2013
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Ingår i: Acta Palaeontologica Polonica. - : Polska Akademia Nauk Instytut Paleobiologii (Institute of Paleobiology, Polish Academy of Sciences). - 0567-7920 .- 1732-2421. ; 58:1, s. 93-109
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 19. |
- Zhang, Zhifei, et al.
(författare)
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An early Cambrian agglutinated tubular lophophorate with brachiopod characters
- 2014
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 4:4682, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- The morphological disparity of lophotrochozoan phyla makes it difficult to predict the morphology of the last common ancestor. Only fossils of stem groups can help discover the morphological transitions that occurred along the roots of these phyla. Here, we describe a tubular fossil Yuganotheca elegans gen. et sp. nov. from the Cambrian (Stage 3) Chengjiang Lagersta¨tte (Yunnan, China) that exhibits an unusual combination of phoronid, brachiopod and tommotiid (Cambrian problematica) characters, notably a pair of agglutinated valves, enclosing a horseshoe-shaped lophophore, supported by a lower bipartite tubular attachment structure with a long pedicle with coelomic space. The terminal bulb of the pedicle provided anchorage in soft sediment. The discovery has important implications for the early evolution of lophotrochozoans, suggesting rooting of brachiopods into the sessile lophotrochozoans and the origination of their bivalved bauplan preceding the biomineralization of shell valves in crown brachiopods.
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