Diversity of Pliocene mysticetes from eastern Japan

Abstract

Abstract Assemblages of Early Pliocene Mysticeti (Cetacea) from the Sendai‐Iwate and Choshi areas in eastern Japan were examined. The early Early Pliocene Tatsunokuchi and Yushima formations of the Sendai‐Iwate area have yielded many cetotheres assigned to Herpetocetus (Cetotheriidae) and some extinct rorquals assigned to Burtinopsis (Balaenopteridae) and other genera. The late Early Pliocene strata of the Na‐arai Formation of the Choshi area has yielded more than 300 mysticete ear bones which fall into seven morphotypes. Assemblages from the two areas differ greatly in taxonomic composition. Archaic mysticetes are dominant in the Sendai‐Iwate area, while modern mysticetes are dominant and diverse in the Choshi area. Based on the results of this study we conclude that the diversity of the Early Pliocene mysticetes in the western North Pacific is comparable to that of the Recent.