Endemic evolution of Tethyan-derived belemnites in North-East Greenland: the middle Barremian Duvalia Event

Field work performed in the years 2007 to 2011 on marine sequences of Early Cretaceous age on Wollaston Forland, North-East Greenland, provided belemnite assemblages from three localities exposing strata of Barremian age. The material analysed here in detail was collected from a ca. 8 m thick sequence of the lower part of the Stratumbjerg Formation of the Rødryggen section.
The most common belemnite genus observed, Oxyteuthis, is of boreal-arctic affinities and closely related to northwest European faunas. Common, co-occurring specimens of Hibolithes show faunal links to both northwest European and Mediterranean faunas. Most remarkable are the findings of 57 rostra of Duvalia, a belemnite genus of Tethyan origin. Apart from Duvalia grasiana the following three taxa have been reognised: Duvalia arctica n.sp., Duvalia aff. silesiaca and Duvalia sp.
Three specimens can be attributed to Duvalia grasiana well known from the Barremian - Aptian of the western Tethys. Most of the material differs, however, morphologically from contemporaneous Duvalia species common in the Barremian of the Tethys. Our findings suggest a migration of D. grasiana to North-East Greenland in the early Barremian and a subsequent in situ evolution of D. arctica n. sp. in the Greenland Norwegian Seaway. Duvalia aff. silesiaca, second in abundance, most likely also evolved from a Tethyan precursor species (Duvalia silesiaca). This latter taxon is, however, not documented in our material. The taxonomic affinities of the third taxon, Duvalia sp. are unclear. D. arctica n. sp., D. aff. silesiaca and Duvalia sp. are all characterised by dwarfism indicating an endemic evolution and adaptation to a well confined position in the food chain. The nitch occupied by the three dwarfed Duvalia species must have differed substantially to that occupied by co-occurring endemic Hibolithes, which have robust, stout rostra. The findings make North-East Greenland part of a migration route from the Tethys via the north Atlantic to the high Boreal. This seaway allowed Tethyan species, which are otherwise unknown from the Boreal Realm, to reach North-East Greenland. The findings also document for the first time a dwarfing effect in belemnites related to an adaptation to a specific nitch in the food chain.