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The significance of the graptoloid Amphigraptus divergens from the (mid-Rawtheyan) type section of the Ashgill Series, Ordovician

Published online by Cambridge University Press:  20 December 2004

R. B. RICKARDS
R. B. RICKARDS
Affiliation:
Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
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Abstract

Amphigraptus divergens Lapworth is known to be restricted, in Britain, to the linearis Biozone, and its occurrence in the type Ashgill Series reinforces Rickards' prior independent attribution of that part of the type Ashgill to the linearis Biozone. The thecal structure revealed in this paper allies A. divergens to the dicellograptids rather than the leptograptids, hence it is placed in the family Dicranograptidae. The evolutionary origin of Amphigraptus is almost certainly rooted in Dicellograptus.

Keywords

Ashgill SeriesOrdoviciangraptolites

Information

Type
Rapid Communication
Information
Geological Magazine , Volume 141 , Issue 6 , November 2004 , pp. 735 - 738
Copyright
© 2004 Cambridge University Press

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