An early and new member of Balaenopteridae from the upper Miocene of Hokkaido, Japan

摘要

The family Balaenopteridae includes the modern blue whale, which is the largest animal on Earth. Our knowledge of the early members of Balaenopteridae, especially during the late Miocene and earlier periods, has recently increased, but this family is still poorly understood. A fossil balaenopterid (including the frontals, squamosals, parietals, vomer, pterygoid, basisphenoid, basioccipital, exoccipitals, right periotic and presternum) from the lower part of the Horokaoshirarika Formation, late Miocene (6.5-6.8 Ma) of Hokkaido, Japan is named as a new genus and species Miobalaenoptera numataensis, and is placed in a phylogenetic context. As a result, Miobalaenoptera numataensis is placed among the stem balaenopterids. The periotic of Miobalaenoptera numataensis shows a deeper suprameatal fossa and a shorter caudal tympanic process than extant species, incipient lateral tuberosity and a sharp anteroposteriorly long ridge on the ventral side of the anterior process. Miobalaenoptera numataensis adds information on the early morphology of the family including the periotic.