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| 4. |
- Holmer, Lars E., et al.
(författare)
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First record of a bivalved larval shell in Early Cambrian tommotiids and its phylogenetic significance
- 2011
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Ingår i: Palaeontology. - : Wiley. - 0031-0239 .- 1475-4983. ; 54:2, s. 235-239
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Hu, Shixue, et al.
(författare)
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Soft-part preservation in a linguliform brachiopod from the lower Cambrian Wulongqing Formation (Guanshan Fauna) of Yunnan, South China
- 2010
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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. ; 55:3, s. 495-505
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Tidskriftsartikel (refereegranskat)abstract
- Linguliform brachiopods were important components of early Cambrian benthic communities. However, exceptionally preserved soft parts in Cambrian linguliform brachiopods are extremely sparse, and the most important findings are from the early Cambrian Chengjiang Konservat Lagerstatte of Kunming, southern China. Here we describe the first record of preserved soft-part anatomy in a linguli form brachiopod from the early Cambrian Guanshan fauna (Wu longging Formation, Palaeolenus Zone); a unit which is considerably younger than the Chengjiang fauna. The well preserved soft anatomy include linguliform pedicles, marginal setae and, in a few cases, an intact lophophore imprint. The pedicle has pronounced surface annulations, with its proximal-most part enclosing the apex of the ventral pseudointerarea; the pedicle is up to 51 mm long, corresponding to more than 4 times the sagittal length of the shell, and 12% of the maximum valve width. In details of their preservation, these new fossils exhibit striking similarities with the linguliforms from the older Chengjiang fauna, and all specimens are preserved in a compressed state as flattened impressions. The new linguliform has an elongate oval to subtriangular shell and an elongate triangular ventral pseudointerarea; the pedicle emerged from an apical foramen through a poorly preserved internal pedicle tube. The new linguliform is most similar to the mostly organic-shelled siphonotretoid-like brachiopod Acanthotretella spinosa, recently described from the classic middle Cambrian Burgess Shale Konservat Lagerstatte, British Columbia, Canada. The new species Acanthotretella decaius sp. nov. is described; it differs from A. spinosa in having a slightly thicker pedicle, and a larger and more rigid, probably partly mineralised shell, indicating that the mostly organic shell of A. spinosa may represent a secondary reduction of shell mineralisation. However, the spine-like setae of the new species are unfortunately poorly preserved only at the margin of the shell, but the new species is referred tentatively to the Superfamily Siphonotretoidea. The occurrence of A. decaius in the Guanshan fauna is the first lower Cambrian (Series 2, early Stage 4) record of both Acanthotretella and siphonotretoids, and it represents the first description of a lophophore and digestive tract from the siphonotretoid lineage.
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| 6. |
- Larsson, Cecilia M
(författare)
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Early Cambrian Problematic Lophotrochozoans and Dilemmas of Scleritome Reconstructions
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 7. |
- Popov, Leonid E., et al.
(författare)
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Earliest ontogeny of Early Palaeozoic Craniiformea : implications for brachiopod phylogeny
- 2010
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Ingår i: Lethaia. - : Scandinavian University Press / Universitetsforlaget AS. - 0024-1164 .- 1502-3931. ; 43:3, s. 323-333
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Tidskriftsartikel (refereegranskat)abstract
- Well preserved specimens of the Early Palaeozoic craniiform brachiopods Orthisocrania and Craniops retain clear evidence of a lecithotrophic larval stage, indicating the loss of planktotrophy early in their phylogeny. The size of the earliest mineralized dorsal shell was <100 mu m across, and the well preserved shell structure in these fossil craniiforms allows their earliest ontogeny to be compared directly with that of living Novocrania, in which the first mineralized dorsal shell (metamorphic shell) is secreted only after settlement of the lecithotrophic larvae. Immediately outside this earliest shell (early post-metamorphic or brephic shell) and in the rest of the dorsal valve the primary layer in both fossil and living craniiforms has characteristic radially arranged laths, which are invariably lacking in the earliest dorsal shell. The ventral valve of the fossil specimens commonly preserves traces of an early attachment scar (cicatrix), which is equal in size to the dorsal metamorphic shell, and the brephic post-metamorphic ventral valve also has a primary shell with radially arranged laths. However, a primary shell with radial laths is completely lacking in the ventral valve of living Novocrania, indicating that heterochrony may have been involved in the origin of the encrusting mode of life in living craniids; the entire ventral valve of Recent craniids (with the possible exception of Neoancistrocrania) may correspond to the earliest attachment scar of some fossil taxa such as Orthisocrania. It is also probable that the unique absence of an inner mantle lobe as well as the absence of lobate cells in Novocrania could be the result of heterochronic changes. The dorsal valve of both fossil and living craniiforms has a marked outer growth ring, around 500 mu m across, marking the transition to the adult, and a significant change in regime of shell secretion. The earliest craniiform attachment is considered to be homologous to the unique attachment structures described recently in polytoechioids (e.g. Antigonambonites) and other members of the strophomenate clade. However, unlike the craniiforms, polytoechioids and strophomenates all have planktotrophic larvae, and planktotrophy is most probably a plesiomorphic character for all Brachiopoda.
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| 8. |
- Skovsted, Christian B., et al.
(författare)
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Early Cambrian brachiopods and other shelly fossils from the basal Kinzers Formation of Pennsylvania
- 2010
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Ingår i: Journal of Paleontology. - 0022-3360 .- 1937-2337. ; 84:4, s. 754-762
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Tidskriftsartikel (refereegranskat)abstract
- An assemblage of seventeen species of Small Shelly Fossils, dominated by the brachiopod Eothele tubulus and species of the mollusk Yochelcionella, is described from the basal Kinzers Formation of Thomasville, Pennsylvania. The occurrence extends southwards the distribution of an Early Cambrian fauna (Cambrian Series 2, Stage 4) that is otherwise characteristic of the eastern shelf of Laurentia from New York to Greenland. The poorly known acrothelid brachiopod Eothele tubulus is redescribed based on large collections of ventral valves. The shell structure of E. tubulus is characterized by orthogonal baculae, and represents the oldest known example of a baculate shell structure, indicating that this type of shell structure evolved already in the Early Cambrian.
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| 9. |
- Skovsted, Christian B., et al.
(författare)
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First occurrence of a new Ocruranus-like helcionelloid mollusc from the lower Cambrian of East Gondwana
- 2012
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Ingår i: Gondwana Research. - : Elsevier BV. - 1342-937X .- 1878-0571. ; 22:1, s. 256-261
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Skovsted, Christian B., et al.
(författare)
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Hyolithellus in life position from the Lower Cambrian of North Greenland
- 2011
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Ingår i: Journal of Paleontology. - : Cambridge University Press (CUP). - 0022-3360 .- 1937-2337. ; 85:1, s. 37-47
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Tidskriftsartikel (refereegranskat)abstract
- Tubular specimens belonging to Hyolithellus from silty dolostones of the basal Aftenstjernesø Formation of North Greenland may represent the first occurrence of this widespread Cambrian fossil in life position. A high proportion of preserved specimens are oriented normal to bedding with the tapering end of the tube down. Occasional undulations in the growth of the tubes indicate that the animal actively adjusted its growth to achieve a vertical orientation in relation to the sediment surface. Increasing thickness of the tube wall towards the tapering end shifted the center of mass downwards and resulted in greater stability in the sediment. The tube remained open at both ends throughout ontogeny; it was most likely secreted by an annelid-grade animal which pumped water into the sediment through the tube. Hyolithellus and similar tubular fossils from the Lower Cambrian probably represent stem group annelids.
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| 11. |
- Skovsted, Christian B., et al.
(författare)
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Sclerite fusion in the problematic early Cambrian spine-like fossil Stoibostrombus from South Australia
- 2011
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Ingår i: Bulletin of Geosciences. - : Czech Geological Survey. - 1214-1119 .- 1802-8225. ; 86:3, s. 651-658
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Tidskriftsartikel (refereegranskat)abstract
- 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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| 12. |
- Skovsted, Christian B., et al.
(författare)
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Scleritome construction, biofacies, biostratigraphy and systematics of the tommotiid Eccentrotheca helenia sp. nov. from the Early Cambrian of South Australia
- 2011
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Ingår i: Palaeontology. - : Wiley. - 0031-0239 .- 1475-4983. ; 54, s. 253-286
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 13. |
- Skovsted, Christian B., et al.
(författare)
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The problematic early Cambrian fossil Tumulduria incomperta represents the detached ventral interarea of a paterinid brachiopod.
- 2014
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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. ; 59:2, s. 359-365
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Tidskriftsartikel (refereegranskat)abstract
- The organophosphatic early Cambrian (Terreneuvian, Cambrian Stage 2) fossil Tumulduria incomperta has been problematic ever since its original description in 1969. Comparison of abundant specimens from the Lower Cambrian of Siberia with co-occurring brachiopod valves show that T. incomperta represents the central portion of the ventral interarea of a paterinid brachiopod similar to Cryptotreta neguertchenensis, and that the domed central portion of typical Tumulduria specimens represents the ridge-like pseudodeltidium of the interarea.
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| 14. |
- Topper, Timothy P., et al.
(författare)
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Microdictyon plates from the lower Cambrian Ajax Limestone of South Australia : Implications for species taxonomy and diversity
- 2011
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Ingår i: Alcheringa. - : Informa UK Limited. - 0311-5518 .- 1752-0754. ; 35:3, s. 427-443
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 15. |
- Topper, Timothy P., et al.
(författare)
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Palaeoscolecid scleritome fragments with Hadimopanella plates from the early Cambrian of South Australia
- 2010
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Ingår i: Geological Magazine. - 0016-7568 .- 1469-5081. ; 147:1, s. 86-97
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Tidskriftsartikel (refereegranskat)abstract
- Phosphatized articulated palaeoscolecid scleritome fragments with attached Hadimopanella Gedik, 1977 plates are described from the lower Cambrian Mernmerna Formation of South Australia. Hadimopanella is principally known from single, isolated, button-shaped, phosphatic sclerites. The new articulated material from South Australia reveals for the first time the configuration of plates referable to Hadimopanella within the scleritome. The scleritome fragments represent the main trunk sections of the cuticle with anterior and posterior terminations lacking. Each annulus on the trunk is ornamented by rows of irregularly alternating Hadimopanella plates. The large majority of plates display a single, centrally located, conical node referable to the form species H. apicata Wrona, 1982. However, individual plates display considerable morphological variation with plates situated along the flattened trunk margin identical to the form species H. antarctica Wrona, 1987. The South Australian material displays the detailed scleritome configuration of cuticular plates and platelets and demonstrates irrefutably that plates of the form species H. apicata and H. antarctica occur as mineralized cuticular elements on the same palaeoscolecid scleritome.
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| 16. |
- Topper, Timothy P., et al.
(författare)
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The oldest bivalved arthropods from the early Cambrian of East Gondwana : Systematics, biostratigraphy and biogeography
- 2011
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Ingår i: Gondwana Research. - : Elsevier BV. - 1342-937X .- 1878-0571. ; 19:1, s. 310-326
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Tidskriftsartikel (refereegranskat)abstract
- The oldest bradoriid fauna from Australia, occurring in the lower Cambrian Ajax and Wirrapowie limestones of the Hinders Ranges, South Australia consists of eleven taxa, including one new genus and species, Quadricona madonnae gen. et sp. nov. and two new species, Liangshanella circumbolina sp. nov. and Zepaera jagoi sp. nov. In the Ajax Limestone, Liangshanella circumbolina sp. nov. occurs c. 20 m below the FAD of the zonal trilobite Abadiella huoi. This pre-trilobitic occurrence represents the oldest bivalved arthropod hitherto known from East Gondwana and suggests a lower Cambrian (Series 2, Stage 3) age for the assemblage. The recognition of distinct bradoriid assemblages associated with the Abadiella huoi (Atdabanian). Pararaia tatei, P. bunyerooensis and P. janeae (all Botoman) trilobite biozones in South Australia indicates great potential for future regional biostratigraphic correlation. Quantitative biogeographic analysis including new taxonomic data from the lower Cambrian of South Australia, highlights the strong endemism displayed by early Cambrian bradoriid communities and strengthens the close faunal affinities with South China and Antarctica.
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