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Trachyplax arctica, a new multiplated problematic fossil from the Lower Cambrian of North Greenland

100%

Larsson C. M., Peel J. S., Hogstrom A. E. S.

Acta Palaeontologica Polonica

2009

tom 54

nr 3

513-523

A new scleritome−bearing organism with eight sclerite types, Trachyplax arctica gen. et sp. nov., is described from the lower Cambrian Paralledal Formation of North Greenland. The originally calcareous sclerites are now silicified; no microstructures are preserved. The dominant sclerite type (A; maximum dimension 19.3 mm) is bilaterally symmetrical, strongly arched, with an oval shield showing co−marginal growth lines and a projecting rostrum with prominent radial ornamentation. A similar sclerite morphology can be identified in Silurian–Carboniferous multiplacophoran molluscs but the remaining sclerite types, which also display a combination of concentric and radial ornamentation, find no clear equivalents. Two models for scleritome reconstruction are presented, based on the relative abundance of the sclerites, but neither promotes a satisfactory assignment to a higher taxon. Despite the morphological dissimilarities, possibly reflecting the age discrepancy, reference to the Multiplacophora is most attractive and entails a substantial extension of the known geological range of that group.

The oldest brachiopods from the lower Cambrian of South Australia

64%

Topper T. P., Holmer L. E., Skovsted C. B., Brock G. A., Balthasar U., Larsson C. M., Stolk S. P., Harper D. A. T.

Acta Palaeontologica Polonica

2013

tom 58

nr 1

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−trilo− bitic (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 Se− ries 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.

Ograniczanie wyników

2 Acta Palaeontologica Polonica

2 Larsson C. M.

1 Balthasar U.

1 Brock G. A.

1 Harper D. A. T.

1 Hogstrom A. E. S.

1 Holmer L. E.

1 Peel J. S.

1 Skovsted C. B.

1 Stolk S. P.

1 Topper T. P.

1 2013

1 2009

Wyniki wyszukiwania

Trachyplax arctica, a new multiplated problematic fossil from the Lower Cambrian of North Greenland

The oldest brachiopods from the lower Cambrian of South Australia