Zalasiewicz, J. A. and Page, A. A. and Rickards, R. B. and Williams, M. and Wilby, P. R. and Howe, M. P. A. (2013) Polymorphic organization in a planktonic graptoloid (Hemichordata: Pterobranchia) colony of Late Ordovician age. Geological Magazine, 150 (1). pp. 143-152. DOI https://doi.org/10.1017/S0016756812000349
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Abstract
Graptolites are common fossils in Lower Palaeozoic strata, but little is known of their soft-part anatomy. However, we report a long-overlooked specimen of Dicranograptus aff. ramosus from Upper Ordovician strata of southern Scotland that preserves a strongly polymorphic, recalcitrant, organic-walled network hitherto unseen in graptoloid graptolites. This network displays three morphologies: proximally, a strap-like pattern, likely of flattened tubes; these transform distally into isolated, hourglass-shaped structures; then, yet more distally, revert to a (simpler) strap-like pattern. The network most likely represents a stolon-like system, hitherto unknown in graptoloids, that connected individual zooids. Its alternative interpretation, as colonial xenobionts that infested a graptoloid colony and mimicked its architecture, is considered less likely on taphonomic and palaeobiological grounds. Such polymorphism is not known in non-graptolite pterobranchs, which are less diverse and morphologically more conservative: a division of labour between graptoloid zooids for such functions as feeding, breeding and rhabdosome construction may have been the key to their remarkable evolutionary success.
Item Type: | Article |
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Uncontrolled Keywords: | 2012AREP; IA63; |
Subjects: | 04 - Palaeobiology |
Divisions: | 04 - Palaeobiology |
Journal or Publication Title: | Geological Magazine |
Volume: | 150 |
Page Range: | pp. 143-152 |
Identification Number: | https://doi.org/10.1017/S0016756812000349 |
Depositing User: | Sarah Humbert |
Date Deposited: | 09 Jul 2012 12:09 |
Last Modified: | 23 Jul 2013 10:04 |
URI: | http://eprints.esc.cam.ac.uk/id/eprint/2556 |
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