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Element association and morphology in some Middle Ordovician platform-equipped conodonts

Published online by Cambridge University Press:  14 July 2015

Anita Löfgren  and
Zhang Jianhua
Anita Löfgren
Affiliation:
Department of Geology, Sölvegatan 13, SE-223 62 Lund, Sweden,
Zhang Jianhua
Affiliation:
Department of Geology and Geochemistry, Stockholm University, Stockholm, Sweden
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Abstract

Conodont elements other than those with platform ledges along the processes have often been unrecognized or disregarded in reconstructions and phylogenetic discussions of Ordovician “platform conodont genera.” The platform elements are larger than the other element types and often exhibit more rapid evolutionary changes in morphology. Nevertheless, to understand the evolution of, and relationships between and among “platform genera,” it is necessary to also consider the associated ramiform and geniculate elements. Thus, on the basis of large collections, together comprising 10,800 elements from Sweden and southern China, all element types of Lenodus antivariabilis (An, 1981), L. variabilis (Sergeeva, 1963), Yangtzeplacognathus crassus (Chen and Zhang, 1993) and Eoplacognathus pseudoplanus (Viira, 1974) are described and discussed. All these species had seven morphologically distinct element types, and probably seventeen individual elements in each apparatus. Ancestors and descendants of these species are discussed more briefly and it is concluded that the ramiform and geniculate elements also are characteristic within each lineage.

Type
Research Article
Information
Journal of Paleontology , Volume 77 , Issue 4 , July 2003 , pp. 721 - 737
Copyright
Copyright © The Paleontological Society

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