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Graptolite synrhabdosomes: biological or taphonomic entities?

Published online by Cambridge University Press:  08 February 2016

Juan Carlos Gutiérrez-Marco
Affiliation:
Instituto de Geología Económica (Consejo Superior de Investigaciones Científicas - Universidad Complutense de Madrid), Facultad de Ciencias Geológicas, 28040 Madrid, Spain. E-mail: [email protected]
Alfred C. Lenz
Affiliation:
Department of Earth Sciences, University of Western Ontario, London, Ontario, Canada N6A 5B7. E-mail: [email protected]

Abstract

Synrhabdosomes, structures made of mostly radially arrayed graptolite rhabdosomes attached by distal regions of their virgulae, have been considered as biological entities by some in the past, but as taphonomic structures by others more recently. Our survey of at least 200 synrhabdosomes, more than 90 of which derive from one locality in northwestern Spain, shows that all synrhabdosomes are most probably entirely monospecific assemblages composed of a more or less finite number of rhabdosomes, all of which are consistently straight or only weakly curved, and all of which bear simple, or relatively simple, thecae. We conclude, therefore, that synrhabdosomes are biological entities, and we suggest that they formed infrequently as, perhaps, temporary structures to increase food-gathering efficiency during times of lower plankton supply in local, relatively restricted water masses.

Type
Articles
Copyright
Copyright © The Paleontological Society 

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