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Abstract
The cephalopods of the reef limestones of the Vasalemma Formation, northern Estonia, are highly diverse and comprise 22 species belonging to 10 families and seven orders in a sample of >300 specimens. Most of the specimens were collected from shell concentrations in synsedimentary cavities and are interpreted as parautochthonous, washed in from nearby habitats. Nearly all of the shells are fragmented and nearly 15% are partially encrusted by epibionts. The assemblage is dominated by small (mostly less than 30 mm wide), straight-shelled actinocerids and orthocerids; in addition, coiled tarphycerids are common. The high-level taxonomic composition of the Vasalemma cephalopod assemblage, with a dominance of actinocerids and an absence of endocerids, is in agreement with deposition in a warm-water (tropical or subtropical), shallow, subtidal regime. At the species level the assemblage is highly endemic, but the generic composition allows for a statistical comparison with other faunas. A cluster analysis of contemporary assemblages reveals a high degree of similarity with late Sandbian cephalopod faunas of epicontinental Laurentia. The palaeogeographical distribution pattern is similar to that of brachiopods, which supports earlier interpretations of these clusters as mainly controlled by water temperature and depositional depth. Several of the Vasalemma genera became conspicuous elements of epicontinental Laurentia during the Katian, which emphasizes that immigration towards Laurentia was an important factor in Late Ordovician diversity dynamics. Of the described taxa, the following are new: Beloitoceras cautis sp. nov., Curtoceras abditus sp. nov., Hemibeloitoceras arduum sp. nov., H. molis sp. nov., Hoeloceras muroni sp. nov., Isorthoceras cavi sp. nov., I. maris sp. nov., I. padisense sp. nov., I. vexilli sp. nov., Ordogeisonoceras tartuensis sp. nov., Orthonybyoceras isakari sp. nov., O. moisense sp. nov., Pleurorthoceras organi sp. nov., Rummoceras rummuensis gen. et sp. nov. and Trocholites gennadii sp. nov.
http://zoobank.org/urn:lsid:zoobank.org:pub:E5211305-A5D0-4366-AAB1-08F96F817122
Acknowledgements
We are indebted for the support by the Deutsche Forschungsgemeinschaft (grant KR 2095/7-1). BK is grateful to Mare Isakar for many years of support during fieldwork and collecting trips in Estonia and for being such good company. We thank Ursula Toom and Gennadi Baranov (Tallinn) for help in the collections, and Olle Hints and Linda Hints (Tallinn) for general support. We thank Helena Korkka (Helsinki) for help with the preparation of the specimens. MA is very grateful to Tõnu Meidla (Tartu) for essential support, useful advice and kind help during her stay and work in the collections, and to Vojtěch Turek and Michal Kubajko (Prague) for kindly providing several well-preserved cephalopod specimens from Vasalemma. MA also wants to thank Martin Košťák (Prague) for general help and advice, and Mikuláš Muroň (Brno) for support and technical help. This research was further supported by European Social Fund's Doctoral Studies, the Internationalisation Programme DoRa. It received support from SYNTHESYS3 which is financed by the European Community–Research Infrastructure Action under the Seventh Framework Programme (FP7/2007-2013, grant agreement no. 226506). This paper is a contribution to IGCP 591 project ‘The Early to Middle Palaeozoic Revolution’.
Supplemental data
Supplemental data for this article can be accessed at https://doi.org/10.1080/14772019.2017.1347212.