Discosorids and Oncocerids (Cephalopoda) of the Middle Ordovician Kunda and Aseri Regional Stages of Baltoscandia and the early evolution of these groups |
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Authors: | Björn Kröger Yunbai Zhang |
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Institution: | a Laboratoire de paléontologie et paléogéographie du paléozoïque (LP3), sciences de la terre, université des sciences et technologies de Lille-1, bâtiment SN5, 59655 Villeneuve-d’Ascq cedex, France b Museum für Naturkunde der Humboldt Universität, Invalidenstrasse 43, 10115 Berlin, Germany c Nanjing Institute of Geology and Palaeontology, 39 East Beijing Road, Nanjing 210008, China d University of Tartu, Tartu ülikool, Geoloogiamuuseum, Vanemuise 46, 51014 Tartu, Estonia |
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Abstract: | Discosorid and oncocerid cephalopods of the Kunda and Aseri Regional Stage (Darriwilian, Middle Ordovician) from Öland Island, Sweden and North Estonia are described for the first time. We demonstrate that a high generic and specific diversity of Oncocerida was already established in the earliest Darriwilian. The new oncocerid species Neumatoceras borense nov. sp., N. breviborense nov. sp., Paramiamoceras breviventrum nov. sp., Richardsonoceras gastroscopium nov. sp., R. gerhardi nov. sp., R. goldmanni nov. sp., R. haelluddenense nov. sp., Richardsonoceroides kingi nov. sp., R. oelandense nov. sp., and R. rhytium nov. sp. are erected; Richardsonoceroides schiefferdeckeri (Dewitz) is revised. The new graciloceratid Kundoceras evansi nov. gen., nov. sp. is erected. A review of records of early oncocerids from China shows that Richardsonoceras Foerste is probably the most primitive oncocerid and supports the hypothesis that oncocerids evolved in the early Floian or latest Tremadocian from a Bassleroceras Ulrich and Foerste-like ancestor. The new discosorid genus Paldoceras nov. gen. and species Paldoceras paldiskense nov. sp. and P. neptunsakerense nov. sp. are erected. These discosorids record the morphological link between the late Darriwilian Ruedemannoceras Flower and the early Floian Apocrinoceras Teichert and Glenister, which is considered to be the earliest discosorid. |
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Keywords: | Darriwilian Oncocerida Discosorida Baltoscandia |
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