Early Bajocian belemnites of Southcentral Alaska: new data and new perspectives on mid-Middle Jurassic Megateuthididae and Belemnopseidae biogeography.

In this study, Lower Bajocian belemnites from Southcentral Alaska are formally investigated and described for the first time. Representatives of the families Megateuthididae (Belemnitina) and Belemnopseidae (Belemnopseina) occur in the Parabigotites crassicostatus to Sphaeroceras oblatum ammonite zones (Propinquans to Humphriesianum chronozones) within the Tuxedni Group of the Cook Inlet region and the Talkeetna Mountains. Among Megateuthididae, we introduce the first records of Brevibelus from Alaska, and the first records of Brevibelus gingensis and Eocylindroteuthis from outside Europe. The new taxa Pseudosimobelus tuxedniensis Dzyuba & C. D. Schraer gen. et sp. nov., Eocylindroteuthis gracilenta Dzyuba & C. D. Schraer sp. nov. and Eocylindroteuthis riegrafi Dzyuba & C. D. Schraer sp. nov. are also described. We conclude from our morphological analysis that Pseudosimobelus gen. nov. represents a transitional form between Megateuthididae and Cylindroteuthididae or may even have been ancestral to the latter. The single rostrum of Belemnopseidae identified herein as Hibolithes? sp. juv. is the earliest record of the family from Alaska. Biogeographically, the belemnites represent pan-Tethyan (Brevibelus and Hibolithes?), typically west Tethyan (Brevibelus gingensis, Brevibelus cf. breviformis and Eocylindroteuthis) and endemic north-east Pacific (Pseudosimobelus gen. nov. and Eocylindroteuthis spp. nov.) elements. These palaeontological data suggest a location of the Peninsular terrane in the Early Bajocian south of the present location. We postulate that the appearance of Brevibelus, Eocylindroteuthis and possibly Hibolithes near the north-western shores of North America in the late Early Bajocian was due to their westward migration via the Hispanic Corridor, the migratory seaway between the western Tethys and the eastern Pacific. [ABSTRACT FROM AUTHOR]