Abstract
We report on the first known occurrences of earliest Cretaceous belemnites in Japan, including: Cylindroteuthis aff. knoxvillensis Anderson (Cylindroteuthididae) from the Mitarai Formation (Berriasian) of the Tetori Group in the Shokawa area, Gifu Prefecture, central Japan; and Hibolithes spp. (Mesohibolitidae) from the Isokusa Formation (Berriasian-Valanginian) in the Kesennuma area, Miyagi Prefecture, and the Koyamada Formation (Berriasian-Valanginian) of the Somanakamura Group in the Minamisoma area, Fukushima Prefecture, both in the South Kitakami region, northeastern Japan. According to belemnite biogeography, Cylindroteuthis is considered a typical Boreal genus and Hibolithes a typical Tethyan genus. The recognition of Tethyan faunal elements in the South Kitakami region, which is presently located farther north than the Tetori region, and Boreal faunal elements in the Tetori region, contributes to the reconstruction of earliest Cretaceous paleogeography and oceanic current systems in the northwestern Pacific during this time. As the ammonoid assemblages of the Mitarai, Isokusa, and Koyamada formations are characterized by dominant Tethyan and Pacific genera and the absence of Boreal elements, it appears that Boreal and Tethyan faunas co-occurred in the paleo-Tetori region in the earliest Cretaceous.
