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

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 <i>Miobalaenoptera numataensis</i>, and is placed in a phylogenetic context. As a result, <i>Miobalaenoptera numataensis</i> is placed among the stem balaenopterids. The periotic of <i>Miobalaenoptera numataensis</i> 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. <i>Miobalaenoptera numataensis</i> adds information on the early morphology of the family including the periotic. http://zoobank.org/urn:lsid:zoobank.org:pub:EBAAD222-1F4C-492B-A75C-74DD3B36EE62

须鲸科（Balaenopteridae）包含现存的蓝鲸——地球上体型最大的动物。目前学界对须鲸科早期类群的认知，尤其是中新世晚期及更早时期的类群，近年虽有所拓展，但该科的整体研究仍较为薄弱。一件产自日本北海道晚中新世（距今6.5–6.8百万年）Horokaoshirarika组下部的须鲸科化石，其保存的骨骼包括额骨、鳞骨、顶骨、犁骨、翼骨、基蝶骨、基枕骨、外枕骨、右侧围耳骨（periotic）及胸骨柄（presternum），该化石被命名为新属新种*Miobalaenoptera numataensis*，并被纳入系统发育分析框架。研究结果表明，*Miobalaenoptera numataensis*隶属于须鲸科的基干类群。该种的围耳骨相较于现存类群，具有更深的上道窝（suprameatal fossa）与更短的尾端鼓室突（caudal tympanic process），同时带有初期发育的外侧结节（lateral tuberosity），且在前突（anterior process）的腹侧存在一条尖锐且沿前后向延伸的长脊。*Miobalaenoptera numataensis*为须鲸科（包括围耳骨在内）的早期形态学研究提供了新的资料。相关信息可通过 http://zoobank.org/urn:lsid:zoobank.org:pub:EBAAD222-1F4C-492B-A75C-74DD3B36EE62 查询。