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A sclerotized retiolitid, and its bearing on the origin and evolution of Silurian retiolitid graptolites

Published online by Cambridge University Press:  20 May 2016

Alfred C. Lenz
Alfred C. Lenz*
Affiliation:
Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7, Canada
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Abstract

The recovery of fully sclerotized specimens of the retiolitid Agastograptus robustus Obut and Zaslavskaya permits the recognition of the relationship between the sicula and thecae 11 and 12 for the first time, and demonstrates unequivocally that the ancora sleeve (the “clathria” of earlier literature) is not homologous with the outer wall of normal diplograptaceans, but is a structure unique to Silurian retiolitids. The study supports earlier proposals that Silurian retiolitids arose, cladogenetically, from Pattern I, ancorate diplograptaceans by distal extension of the ancora/corona, to form the ancora sleeve, but further suggests that the sclerotization of the original diplograptacean outer wall (corresponding to the inner wall of the retiolitid of this study) was suppressed.

Type
Research Article
Information
Journal of Paleontology , Volume 68 , Issue 6 , November 1994 , pp. 1344 - 1349
Copyright
Copyright © The Paleontological Society 

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