Large belemnites were already common in the early Jurassic-New evidence from Central Japan

Belemnites were a highly successful group of Mesozoic cephalopods. Their early evolutionary history is, however, still poorly understood. Previously it has been suggested that the Order Belemnitida originated in the earliest Jurassic (Hettangian) with small forms in Europe, and their occurrence was restricted to Europe until the Pliensbachian. Here we report a large specimen of the Suborder Belemnitina from the upper Pliensbachian of the Kuruma Group in Central Japan. This is the first reliable record of Pliensbachian belemnites from outside Europe and the Mediterranean area. The specimen from Japan differs from those of the coeval European genera by its large rostrum. The rostrum diameter of this specimen rather resembles that of the Middle Jurassic belemnite genus Megateuthis, the largest belemnite ever observed. This new finding provides additional evidence of the existence of belemnites with extremely large rostra in the Early Jurassic of the western paleo-Pacific area, thereby shedding new light on the early evolutionary history of belemnites.