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1 September 2009 Trachyplax arctica, a New Multiplated Problematic Fossil from the Lower Cambrian of North Greenland
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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.

Cecilia M. Larsson, John S. Peel, and Anette E.S. Högström "Trachyplax arctica, a New Multiplated Problematic Fossil from the Lower Cambrian of North Greenland," Acta Palaeontologica Polonica 54(3), 513-523, (1 September 2009).
Received: 6 March 2009; Accepted: 1 July 2009; Published: 1 September 2009

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