Minimum bones of the biggest ever animals: form, function, and evolution of ear ossicles in baleen whales

Research Project

Project/Area Number	16K21437
Research Category	Grant-in-Aid for Young Scientists (B)
Allocation Type	Multi-year Fund
Research Field	Stratigraphy/Paleontology Morphology/Structure
Research Institution	Shumei University
Principal Investigator	Murakami Mizuki 秀明大学, 学校教師学部, 講師 (70710614)
Project Period (FY)	2016-04-01 – 2019-03-31
Project Status	Completed (Fiscal Year 2018)
Budget Amount *help	¥4,160,000 (Direct Cost: ¥3,200,000、Indirect Cost: ¥960,000) Fiscal Year 2018: ¥650,000 (Direct Cost: ¥500,000、Indirect Cost: ¥150,000) Fiscal Year 2017: ¥1,300,000 (Direct Cost: ¥1,000,000、Indirect Cost: ¥300,000) Fiscal Year 2016: ¥2,210,000 (Direct Cost: ¥1,700,000、Indirect Cost: ¥510,000)
Keywords	ヒゲクジラ / 耳小骨 / 形態 / 進化 / ツチ骨 / アブミ骨 / 形態比較 / 系統 / 機能
Outline of Final Research Achievements	For the purpose of clarifying morphological differences of ear ossicles in Mysticeti, ear ossicles of 17 mysticetes were compared. As a result, morphological differences of ear ossicles in mysticete families are shown, even though those differences have been believed that those were small. For example, the anterior process of malleus in Balaenopteridae dorsoventrally thick relative to those of Balaenidae, Eschrichtidae，and Cetotheriidae, because dorsal part of manubrium of Balaenopteridae is not swollen. Furthermore, malleus of Eschrichtidae is wide in medially, and the articular surfaces of incus is warped. Stapes of Bowhead whale is clearly long relative to those of archaeocetes and other mysticetes, although morphological differences of stapes are small relative to those of malleus. Thus, morphology of ear ossicles in mysticetes reflect phylogenetc relationships, these may evolved with their ecology.
Academic Significance and Societal Importance of the Research Achievements	ヒゲクジラ類の耳小骨は，下顎骨-音響脂肪-鼓室骨と伝達されてきた音を，内耳に伝える重要な働きを有している．耳骨のうち，鼓室骨や耳周骨に関しては形態や機能といった観点から多くの研究が行なわれてきたが，耳小骨の形態と機能に関する研究は種ごとの記載でさえごくわずかしか行なわれてこなかった．本研究では，17種のヒゲクジラ類に関して耳小骨の形態比較を行ない，形態的な差違が軽視されてきたヒゲクジラ類においても，耳小骨は各科ごとに形態変異があることを明らかにした．本研究はで初めて明らかになった形態差異は、ヒゲクジラ類の鳴音の進化がどのようにおこったのか理解する上で重要である．