期刊
GEOLOGICAL MAGAZINE
卷 150, 期 1, 页码 143-152出版社
CAMBRIDGE UNIV PRESS
DOI: 10.1017/S0016756812000349
关键词
polymorphism; graptolite; zooplankton; Ordovician; soft anatomy; xenobionts
资金
- NERC [bgs05001, bgs05002] Funding Source: UKRI
- Natural Environment Research Council [bgs05002, bgs05001] Funding Source: researchfish
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 constructionmay have been the key to their remarkable evolutionary success.
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