Survival and recovery atrypid fauna following the terminal Ordovician extinction, the Atrypinae: central Oslo Region, Norway

ABSTRACT

The atrypid fauna immediately following the end-Ordovician extinction event is poorly known. Siliciclastic strata of the Solvik Formation in the central Oslo region was deposited during the latest Hirnantian into the Aeronian and contains an uncommonly rich atrypid fauna. The brachiopod subfamily Atrypinae includes three new genera; Askerina, Nottina and Sifella, and six new species; Askerina cymbula, Dihelictera askeriensis, Joviatrypa nakremi, Nottina phalerata, Sifella patera and Zygospiraella nupera. Schachriomonia spiraensis sp. nov. (subfamily Spirigerininae) shows transitional traits to the subfamily Atrypinae. Free-lying, relatively large-shelled genera with many-whorled spiralia and frills like Atrypa developed earlier than previously known with the new genus Askerina occurring in the Ordovician/Silurian boundary layers. A possible gradual evolutionary lineage from Zygospiraella duboisi to Z. nupera sp. nov. is explored. Well-developed fossil assemblages are present from the base of the Solvik Formation. The Formation was deposited at varying depths with deeper shale facies inhabited by Atrypinae like Askerina, Schachriomonia and Protatrypa, shallower calcareous facies showcase Nottina and Dihelictera, whereas the storm-dominated, Aeronian parts of the formation include species of Joviatrypa, Sifella, Zygospiraella and Gotatrypa? Baltica situated in southern tropical to subtropical latitudes had migration of taxa from east to west following the tropical storm track.

KEYWORDS:

• Lower Llandovery Series
• brachiopods
• Atrypida
• recovery end-Ordovician mass extinction
• evolutionary lineages
• Baltica

Acknowledgments

First and foremost I thank my partner Markes Johnson, Williams College, for steady support, companionship in the field and help with the English. The comments of two anonymous reviewers greatly improved the manuscript. I am also indebted to Hans Arne Nakrem of the Natural History Museum in Oslo who made the collections available and often accompanied me in the field. The Geosciences Department at Williams College kindly provided unrestricted access to the lab and equipment facilities, where I spent countless hours making thin sections. Mea Cook let me use her lab for photography. I also want to thank Paul Copper, Prayssac, France, Jisuo Jin, University of Ontario, and Rong Jiayu and Bing Huang, Nanjing Institute of Geology and Palaeontology, for help with specific questions at different stages of this project.

Disclosure statement

No potential conflict of interest was reported by the author.