Fossil Herpetocetine Baleen Whales (Cetacea, Mysticeti, Cetotheriidae) from the Lower Pliocene Horokaoshirarika Formation at Numata, Hokkaido, Northern Japan

Two mandibles of fossil mysticetes from the early Pliocene, upper part of the Horokaoshirarika Formation at Numata Town, Hokkaido, Japan, belong to the archaic, extinct cetotheriid baleen whale, Herpetocetinae gen. et sp. indet. by having an elongated angular process projecting posteriorly beyond the mandibular condyle. The new materials of the Herpetocetinae represent their northernmost occurrence in the North Pacific.