The cephalopods of the Kullsberg Limestone Formation, Upper Ordovician, central Sweden and the effects of reef diversification on cephalopod diversity

Abstract

The cephalopods collected from the mud mounds of the Kullsberg Limestone Formation, late Sandbian–earliest Katian(?), south central Sweden, are highly diverse and comprise 26 identifiable species of 12 families and six orders in a sample of c. 180 specimens. The assemblage is strongly dominated by orthocerids in abundance and diversity. In contrast, the time-equivalent assemblage of the reef limestone of the Vasalemma Formation of Estonia is dominated by actinocerids and less diverse. Only one-third of the species co-occur in these two palaeogeographically relatively close assemblages. The taxonomic composition of the Kullsberg assemblage is, on the order level, more similar to that of the late Katian–early Hirnantian Boda Limestone Formation of south central Sweden, which represents a similar relatively deep depositional environment. The high local differentiation of cephalopod reef faunas exemplifies the importance of the emergent Baltic reef habitats in diversification processes during the early Late Ordovician. Of the described taxa, the following are new: Beloitoceras thorslundi sp. nov., Cameroceras motsognir sp. nov., Clothoceras thornquisti gen. et sp. nov., Danoceras skalbergensis sp. nov., Discoceras amtjaernense sp. nov., D. nilssoni sp. nov., Endoceras naekki sp. nov., Furudaloceras tomtei gen. et sp. nov., Isbergoceras consobrinum gen. et sp. nov., I. niger gen. et sp. nov., Isorthoceras nikwis sp. nov., I. sylphide sp. nov., I. urdr sp. nov., I. verdandi sp. nov., Kullsbergoceras nissei gen. et sp. nov., Ordogeisonoceras uppsalaensis sp. nov. and Valkyrioceras dalecarlia gen et sp. nov.

http://zoobank.org/urn:lsid:zoobank.org:pub:F5243F9B-547C-424F-895F-6CCECA8BBF11

Keywords:

• Great Ordovician Biodiversification Event (GOBE)
• bioherm
• palaeogeography
• Sandbian Stage
• Katian Stage
• Guttenberg Carbon Isotope Excursion (GICE)

Acknowledgements

We are grateful to Jan Ove Ebbestad (Uppsala, Sweden) and Christian Skovsted (Stockholm, Sweden), for their general support of our collection work. We would also like to express our thanks to Christian Klug (Zürich, Switzerland) for a careful review of and constructive comments on our work. BK was supported by the Deutsche Forschungsgemeinschaft (grant KR 2095/7-1). MA 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 the IGCP 653 project ‘The Onset of the Great Ordovician Biodiversification Event’.

Supplemental material

Supplemental material for this article can be accessed at: https://doi.org/10.1080/14772019.2018.1491899.