The Late Ryazanian – Early Hauterivian ammonite fauna of North-East Greenland is unusually rich, diverse, and dominated by Boreal polyptychitids but also contains a significant number of Tethyan taxa. The fauna is best known from highly fossiliferous localities on Traill 0, but only a small part of the fauna was described more than 50 years ago. The original material and additional collections from Traill 0 and the Wollaston Forland form the basis of a full description and revision of the fauna.
Over 70 ammonite species are described and include 13 new species and one new subgenus: Tollia (Neocraspedites) pentagonalis sp. nov., T. (N.) piaseckii sp. nov., T. (N.) rutila sp. nov., Menjaites (Menjaites) groenlandicus sp. nov., M. (Surlykites) surlyki subgen. nov. et sp. nov., Polyptychites (Polyptychites) robertsi sp. nov., P. (P.) rawsoni sp. nov., P. (P.) copiocostatus sp. nov., P. (P.) rubricosussp. nov., P. (Euryptychites) molsbergensis sp. nov., P. (E.) subcoronatus sp. nov., P. (E.) roemeri sp. nov., and Dichotomies mackneyi sp. nov. One new nautiloid species, Paracymatoceras rufum sp. nov., is also described.
The first Upper Ryazanian – Lower Hauterivian ammonite zonation in North-East Greenland is established, with 11 zones, partly adopted from extant schemes elsewhere. The Upper Ryazanian is represented by the Analogus, Tzikwinianus, and Albidum Zones adopted from the Russian Platform and Siberia. The Lower Valanginian is represented by the Undulatoplicatilis, Hoplitoides, and Michalskii Zones adopted from the Russian Platform. The Upper Valanginian is represented by the Hollwedensis, Crassus, and Bidichotomoides Zones adopted from the NW European (German) zonation. The Lower Hauterivian is represented by the first Simbirskites recorded in North-East Greenland. The fauna occurs in a thin interval of grey and red mudstones of the Albrechts Bugt and Rødryggen Members, respectively. The interval is characterized by major changes in the depositional environment, ecology, and biogeography, and represents a time of major palaeoceanographic change. Possibly, deep water formed in the Polar Boreal Sea and resulted in a southwards-flowing bottom current, which ventilated the water masses in the narrow epeiric seaway between Eastern Greenland and Norway. In response, a surface counter-current flowing towards the north allowed ammonite taxa to migrate thousands of kilometres from Tethys and become important elements in the North-East Greenland fauna.