Gastropods and tergomyans from the Upper Ordovician (Viru–Harju) of the Fågelsång area, Scania, southern Sweden

Abstract

A diverse tergomyan and gastropod assemblage is described from the Global Boundary Stratotype Section and Point (GSSP) section of the Sandbian Stage, Upper Ordovician, in the Fågelsång area, Scania, southern Sweden. Deep water graptolitic mudstone and shale comprise the succession, and previously only one gastropod species was known. The new material spans the Sularp Formation through the Lindegård Mudstone (Nemagraptus gracilis–Dicellograptus complanatus biozones). Fourteen species are described: two tergomyan, five bellerophontoid gastropods, and seven anisostrophically coiled gastropods. Three species are new: Peelerophon hodites, Tetranota scanica and Lophospira sandbiana. Three taxa (Tritonophon subtrilobatus, Tetranota scanica and Holopea mobergi) are found high in the Lindegård Mudstone (Vormsi–Pirgu stages). Cyrtodiscus, Peelerophon and Tritonophon are recorded for the first time in Baltoscandia. Some taxa may have been transported from shallower water settings, whereas species of Peelerophon, Joleaudella, Mestoronema and Sinuites may have been part of the local benthos. Except for Bucania erratica, no species are shared with the fauna of the coeval Dalby Limestone in Sweden. Deaechospira elliptica, common in the Dalby Limestone, is not recorded at Fågelsång, although two closely related species are found (Deaechospira rotunda and Deaechospira? sp.). The Fågelsång assemblage has more in common with the older to coeval fauna of the Elnes and Arnestad formations in the Oslo Region, Norway (e.g. sharing Joleaudella, Sinuites, Mestoronema and Pararaphistoma). The Sandbian fauna of Fågelsång includes peri-Gondwanan taxa, e.g. Cyrtodiscus, Peelerophon and Deaechospira. Nevertheless, cluster analysis reveals that the faunas of Baltica and Laurentia were most similar, whereas faunas from Perunica and Baltica remained distinct and separated during the Darriwilian–Sandbian. The few similarities may result from spread of a temperate fauna supplementing rather than replacing taxa in deep water assemblages. The main Fågelsång assemblage coincides both with the Baltoscandian Middle Caradoc Faunal Turnover and the Gutenberg Carbon Isotope Excursion.

http://zoobank.org/urn:lsid:zoobank.org:pub:093F6504-B3FA-42A4-94C2-FF460D549F18

Keywords:

• gastropods
• tergomyans
• deep water
• palaeobiogeography
• Sandbian
• Mid Caradoc Faunal Turnover

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Erratum

Acknowledgements

The late Maurits Lindström (Stockholm) is thanked for information regarding his collections from Sularp and thoughts on the stratigraphy and depositional environment of the Fågelsång sediments. Stig M. Bergström (Ohio) provided detailed information on Fågelsång stratigraphy, while David L. Bruton (Oslo) and Jesper Hansen (Tromsø) helped with questions concerning stratigraphy in the Oslo Region. Andrei Dronov (Moscow) and Leonid E. Popov (Cardiff) kindly provided help with Russian stratigraphy and localities. Malgorzata Moczydlowska (Uppsala) provided help with translation of Russian text. Per Ahlberg (Lund) kindly helped with access to the Fågelsång collections, while Kent Larsson (Lund) is thanked for help with loans of specimens from the type and main collections. Review by John S. Peel (Uppsala) of an early version of the text greatly improved the manuscript. Mats Eriksson (Lund) and Peter J. Wagner (Washington) are thanked for insightful and detailed reviews of the manuscript.