A new beardfish (Teleostei, Polymixiiformes) from the Eocene Fur Formation, Denmark

ABSTRACT

The earliest Eocene (Ypresian) Fur Formation (Denmark) is globally renowned for its exceptionally well-preserved fossils, including birds, sea turtles, insects, plants, and fishes. Fishes, albeit abundant and diverse, however, are only superficially known and very few detailed, taxonomic studies have been realized to date. A new polymixiiform fish, Polyspinatus fluere gen. et sp. nov., from the Fur Formation is described based on seven well-preserved, nearly complete specimens. All the specimens were studied by traditional stereomicroscopy, and by micro-X-ray fluorescence-element mapping. Digital 2D-element images of strontium-, phosphorus-, and calcium distributions of each specimen were directly applied for the taxonomic descriptions presented herein. Polyspinatus fluere gen. et sp. nov. is the first known Eocene record of the family Polymixiidae based on articulated skeletal remains. Polyspinatus gen. nov. exhibits a unique combination of characters that support its recognition as a new genus of the Polymixiidae. Its specialized hyoid apparatus with the first and second branchiostegal rays being sinuous and parallel to each other, and the third being wide and plate-like, followed by four saber-like elements, is strikingly similar to that of Polymixia, supporting a possible sister-group relationship with extant beardfishes.

ACKNOWLEDGMENTS

We would like to thank H. Madsen for collecting and acid preparing the holotype specimen, which was declared Danekræ fossil trove in December 2020. He also collected and prepared four of the paratypes. We wish to thank B. E. K. Lindow (Natural History Museum of Denmark, Copenhagen University), R. L. Sylvestersen (Fur Museum, Museum Salling), and H. Madsen (Fossil- og Molermuseet, Museum Mors) for access to and loan of fossil material housed in the respective museum collections. AES wishes to thank D. K. P. Wielandt (Natural History Museum, Denmark, Copenhagen University and DANAK) and M. Storey (Natural History Museum, Denmark, Copenhagen University) for invaluable help with and access to the Bruker M4 Tornado, and B. E. K. Lindow for valuable and interesting discussions on vertebrate anatomy relating to the Fur Formation fossil fauna. This research was supported by the Innovation Fund Denmark (8118-00005B), Kulturministeriets Forskningsmidler (FORM.2019-0028), by Dronning Margrethe and Prins Henriks Fond, and by two personal grants (Japetus Steenstrup legat) to AES. The research of GC was supported by grants (ex-60% 2021) from the Università degli Studi di Torino. We wish to thank A. F. Bannikov and T. Přikryl for constructive comments and suggestions.