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Article: New evidence of a spiriferide ancestor for the Thecideidina (Brachiopoda)

Publication: Palaeontology
Volume: 27
Part: 4
Publication Date: December 1984
Page(s): 857 866
Author(s): P. G. Baker
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How to Cite

BAKER, P. G. 1984. New evidence of a spiriferide ancestor for the Thecideidina (Brachiopoda). Palaeontology27, 4, 857–866.

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Investigation of the microstructure of the ventral interarea of a juvenile denticulate spiriferacean assignable to Unispirifer reveals rod-like structures which, apart from a difference in size, are structurally almost identical with the tubercle cores of a recently discovered Aalenian thecideidine species Mimikonstantia sculpta Baker and Elston, 1984. The coincidence of cyrtomatodont teeth, shell resorption, and secondary fibrous shell, together with rod-like granular calcite structures ensheathed in secondary fibres, links the thecideidines with denticulate spiriferaceans. Comparison of the thecideidine shell microstructure with that of a stropheodontid strophomenide Amphistrophia has failed to reveal comparable microstructural elements. The new evidence indicates that the spiriferacean denticle is a structural homologue of the thecideidine tubercle and, from a systematic point of view, removes any remaining objection to the formal assignment of the Thecideidina as a suborder of the Spiriferida. The morphological similarity between thecideidines, suessiacean spiriferides, and certain davidsoniacean and productidine strophomenides is now regarded as an expression of homoeomorphy.
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