Polymorphic organization in a planktonic graptoloid (Hemichordata: Pterobranchia) colony of Late Ordovician age
Zalasiewicz, Jan A.; Page, Alex; Rickards, R. Barrie; Williams, Mark; Wilby, Philip R.; Howe, Michael P.A.; Snelling, Andrea M.. 2013 Polymorphic organization in a planktonic graptoloid (Hemichordata: Pterobranchia) colony of Late Ordovician age. Geological Magazine, 150 (1). 143-152. https://doi.org/10.1017/S0016756812000349
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Abstract/Summary
Graptolites are common fossils in Early Palaeozoic strata, but little is known of their soft-part anatomy. However, we report a long-overlooked specimen of Dicranograptus aff. ramosus from Late 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: | Publication - Article |
|---|---|
| Digital Object Identifier (DOI): | https://doi.org/10.1017/S0016756812000349 |
| ISSN: | 0016-7568 |
| Date made live: | 21 Mar 2013 12:01 +0 (UTC) |
| URI: | https://nora.nerc.ac.uk/id/eprint/500617 |
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