| 1. |
- Peel, John S.
(författare)
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A priapulid larva from the middle Cambrian (Wuliuan Stage) of North Greenland (Laurentia)
- 2022
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Ingår i: Bulletin of Geosciences. - : Czech Geological Survey. - 1214-1119 .- 1802-8225. ; 97:4, s. 445-452
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Tidskriftsartikel (refereegranskat)abstract
- A single phosphatised specimen from the middle Cambrian Henson Gletscher Formation (Miaolingian Series, Wuliuan Stage) of North Greenland is interpreted as the hatching larva of a total-group priapulid worm. A plated lorica is not present but probably was developed at a later larval stage, by comparison with the described development of extant Priapulus caudatus and Halicryptus spinulosus. A characteristic priapulid introvert with scalids is not seen but it was likely withdrawn in the available specimen. The new find is consistent with a similar ontogeny in Cambrian priapulid cycloneuralians to that seen in their present day relatives. New taxon: Inuitiphlaskus kouchinskyi gen. et sp. nov.
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| 2. |
- Peel, John Stuart
(författare)
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Musculature and shell microstructure of the ancestral bivalve Fordilla (Mollusca) from the lower Cambrian of Greenland (Laurentia)
- 2023
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Ingår i: Bulletin of Geosciences. - : Czech Geological Survey. - 1214-1119 .- 1802-8225. ; 98:4, s. 265-287
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Tidskriftsartikel (refereegranskat)abstract
- Shell microstructure and exquisite details of muscle attachment scars are preserved on the surface of internal moulds in the bivalve Fordilla troyensis from the Aftenstjerneso Formation (Cambrian Series 2, Stage 4) of North Greenland (Laurentia). Subsidiary muscles developed in commarginal series that extend laterally from the anterior and posterior adductor muscles probably controlled the centrally emergent foot. Their position close to the ventral margin indicates that only slight withdrawal and limited manipulation of the foot was possible, confirming that Fordilla was not a burrower. The pattern suggests derivation of Fordilla from a clamping mollusc with shell muscles distributed around the shell margin. No such pattern of serially repeated muscles close to the shell margin is currently known in the few available records of helcionelloid muscle scars, but Postacanthella has a commarginal U-shaped muscle scar reflecting its limpet-shaped shell form. Shell microstructure in Fordilla troyensis is closely similar to Pojetaia, with central areas of the valves dominated by a laterally continuous imbricate lamellar structure with a width of 10-20 mu m between successive crests. Imbricate lamellae with about half this spacing form a marginal zone with crests lying perpendicular to the valve edge. The hinge line lacks teeth, although a single tooth is present in each valve of the related Fordilla sibirica and Fordilla germanica. The site of the simple ligament is coarsely striated. Comparative material of Fordilla troyensis is illustrated from New York State, North-East Greenland and Denmark.
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| 3. |
- Peel, John S.
(författare)
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Ontogeny, morphology and pedicle attachment of stenothecoids from the middle Cambrian of North Greenland (Laurentia)
- 2021
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Ingår i: Bulletin of Geosciences. - : Czech Geological Survey. - 1214-1119 .- 1802-8225. ; 96:4, s. 381-399
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Tidskriftsartikel (refereegranskat)abstract
- The bivalved calcareous shells of stenothecoids are generally both inequilateral and inequivalve. They occur in lower and middle Cambrian strata from Laurentia, Siberia, Kazakhstan and China, but their affinities are unresolved. Contemporary workers favour assignment as a separate class of Mollusca or within the stem-group of Brachiopoda. The latter is supported by the present description of pedicle attachment in stenothecoids from the Henson Gletscher Formation (Miaolingian Series, Wuliuan Stage) of North Greenland. Described material from Greenland is mainly preserved as internal moulds showing a high degree of variability that frustrates comparisons with assemblages from other localities and horizons, but provides insight into central features of stenothecoid morphology. Curvature of individual valves is shown to be an unreliable morphological indicator in the North Greenland sample. Early juveniles of Stenothecoides are described confirming the development of a transverse tooth in the interior of the ventral valve throughout ontogeny. A pitted structure near the apex of juvenile internal moulds is interpreted as the scar of a fibrous pedicle attaching the ventral valve to the substrate. Frondose impressions on the shell interior, previously considered to be characteristic of Bagenovia, are described in Stenothecoides. Multiple median scars on the dorsal valve characteristic of Stenothecella (Cambrian Stage 4) are also described in the Wuliuan material from North Greenland. New species: Stenothecoides terraglaciei sp. nov.
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| 4. |
- Peel, John Stuart
(författare)
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Pseudomyona from the Cambrian of North Greenland (Laurentia) and the early evolution of bivalved molluscs
- 2021
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Ingår i: Bulletin of Geosciences. - : CZECH GEOLOGICAL SURVEY. - 1214-1119 .- 1802-8225. ; 96:2, s. 195-215
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Tidskriftsartikel (refereegranskat)abstract
- The laterally compressed, univalve, Cambrian (Miaolingian Series, Drumian Stage) mollusc Pseudomyona is recorded for the first time from Laurentia. Distinctive internal moulds of the type species Pseudomyona queenslandica, a species otherwise known from Australia and northern Siberia, are described from the Ekspedition Brae Formation of southern Lauge Koch Land, North Greenland. A new species, Pseudomyona groenlandica, characterised by a proliferation of hinge teeth on the supra-apical surface, is described from the overlying Fimbuldal Formation of south-east Freuchen Land. The increase in hinge teeth supports the hypothesis that the bivalved Tuarangia from the Miaolingian Series (Guzhangian Stage) of New Zealand and Bornholm, Denmark, evolved from Pseudomyona. Although bivalved, Tuarangia is not interpreted as Class Bivalvia, but as the most derived member of an early clade in the evolution of Class Rostroconchia. The emended Order Tuarangiida, containing Tuarangia and Pseudomyona, forms a sister group to ribeirioids and later rostroconchs
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| 5. |
- Peel, John S.
(författare)
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The oldest palaeoloricate mollusc (Cambrian Series 2, Stage 4; North Greenland) and its bearing on aculiferan evolution
- 2020
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Ingår i: Bulletin of Geosciences. - : CZECH GEOLOGICAL SURVEY. - 1214-1119 .- 1802-8225. ; 95:2, s. 127-144
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Tidskriftsartikel (refereegranskat)abstract
- In the Aculifera Conchifera model of molluscan evolution, spiculate aplacophorans and polyplacophorans with a dorsal series of shell plates are recognised as sister groups within the Glade Aculifera, itself a sister group of the Glade Conchifera that contains all other molluscs. While aculiferans and conchiferans had their common origin near the Precambrian Cambrian boundary, the crown groups of most major molluscan classes are seen traditionally to have emerged in the latest Cambrian (Furongian) Early Ordovician. JI,latthevia Walcott, 1885, from the latest Furongian Early Ordovician of Laurentia, has been regarded almost universally as the oldest undoubted fossil chiton, a palaeoloricate. Palaeoloricates, however, are paraphyletic and Alatthevia is variously interpreted as a time indicator for the origin of crown group Aculifera, within either the stem or crown groups of Aplacophora or Polyplacophora. The discovery of rare disarticulated plates from the early Cambrian (Cambrian Series 2, Stage 4) of North Greenland (Laurentia) extends the geological record of palaeoloricates by about 25 Ma. In bridging the gap between lower stem group aculiferans and the occurrence of Alcuthevia, the new finds offer the potential for a corresponding earlier origin of both aplacophorans and polyplacophorans within the aculiferan crown group. Head and intermediate plates are described from the Aftenstjemeso Formation and placed within a new taxon proposed as Qaleruagia sodermanorum gen. et sp. nov.
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