Aptian and Albian ammonites of the Miyako Group, Japan

Thirty-four upper Aptian to lower Albian ammonite species from the Miyako Group, northeast Japan are described herein: seven phylloceratids, three lytoceratids, one gaudryceratid, one tetragonitid, one oppelid, eight desmoceratids, one cleoniceratid, one hoplitid, three ptychoceratids, four anisoceratids, two douvilleiceratids, and two parahoplitids. Among the described species, Valdedorsella kasei, Diptychoceras iwatense, Protanisoceras (P.) hanaii, and Hypacnthoplites regina are proposed as new species. To date, fifty-five species belonging to 35 genera have been described from the ammonite fauna of the Miyako Group. This ammonite fauna can be subdivided into three ammonite biostratigraphic zones (Hypacanthoplites subcornuerianus Zone, Diadochoceras nodosocostatiforme Zone and Douvilleiceras mammilatum Zone in ascending order), and these zones are defined. These zones can be correlated with the upper Aptian to lower Albian of the European standard zonation. Ammonites of the Miyako Group diversified morphologically with transgression, and expanded the range of their habitation area. This expansion developed by chance at approximately the even level for each taxon. Ammonite biogeography is interpreted to be controlled by oceanic currents of the circum Pacific rim.