The genus Hourcquia (Ammonoidea, Pseudotissotiidae) from the Upper Cretaceous of Hokkaido, Japan : biostratigraphic and biogeographic implications

Abstract

Stratigraphic and ontogenetic descriptions of three species of Hourcquia from the Cretaceous Yezo Supergroup of Hokkaido, Japan are given for the first time. H. ingens, H. hataii and H. kawashitai occur in the Inoceramus teshioensis Zone of the upper Turonian. Hourcquia evolved and radiated in not only the Tethyan and adjacent areas but also the Northwest Pacific region for a short period in the late Turonian.