第 13 期白眉研究者紹介● グローバル型（従来型）／ Global Type

Introduction of 13th-batch Hakubi Researchers★ 部 局 連 携 型（卓越研究員型）／ Tenure ‒Track Type● 田近 周 特定助教
Amane TAJIKA (Assistant Professor)
研 究 課 題： 白亜紀末大量絶滅事変における海洋酸性化イベントの復元による頭足類絶滅メカニズムの解明（Investigating the link between ocean acidiﬁcationand selective extinction of cephalopods）
専 門 分 野： 古生物学（Paleontology）
受 入 先 部 局： 人間・環境学研究科（Graduate School of Human and Environmental Studies）
前職の機関名： 東京大学総合研究博物館・チューリッヒ大学古生物学研究所（University Museum, University of Tokyo / Paleontological Institute, University of Zurich）

私の専門は古生物学という地球史において絶滅したEnvironmental changes and resulting species diversity loss

生物に関する研究を行う分野です。私はこれまで海棲無KDYHEHFRPHPDMRULVVXHVLQWKHPRGHUQZRUOG,QRUGHUWR
better understand our current situation, it is necessary to look

脊椎動物を中心に研究を行ってきました。海棲無脊椎動

at Earth history. As a paleobiologist, I have attempted to an-

物は化石記録が豊富であり、化石を用いて進化や絶滅にVZHU TXHVWLRQV UHJDUGLQJ HQYLURQPHQWDO FKDQJHV DQG WKHLU

関する様々な研究をすることが可能です。

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私の白眉プロジェクトにおける研究では、白亜紀末に7KH.3JPDVVH[WLQFWLRQHYHQWLVRQHRIWKH³%LJ¿YH´PDVV

起きた大量絶滅事変に注目し研究を行います。白亜紀のextinctions, in which the taxonomic diversity significantly

大量絶滅事変では地球上に生息する約 75％の生物種がdecreased. Studying such a mass extinction event can provide

絶滅したと考えられています。その中で頭足類（イカやimportant insights into the ecological and evolutionary impacts caused by rapid environmental changes. In the marine

タコの仲間）においては、類似した殻形態をもつアンモ

realm, the selective extinction in cephalopods, which include

ナイト類は絶滅し、オウムガイ類は絶滅を免れています

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が、その絶滅の選択性についての詳細は解明されていま

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せん。本研究では、過去の古環境変動復元と殻形態の変

nautiloids, despite their similar external shells, experienced化を高解像度で分析することによって白亜紀末におけGUDVWLFDOO\GL൵HUHQWIDWHVGXULQJWKLVHYHQW$PPRQRLGVPHW

る頭足類の絶滅の選択性について解明を目指します。

their end, while nautiloids survived the mass extinction.
While several hypotheses have been postulated in previousstudies, the definitive cause of this selective extinction remains shrouded in mystery. With the application of advanced
JHRFKHPLFDODQGWRPRJUDSKLFWHFKQLTXHV,DLPWRXQHDUWKthe mechanisms behind the selective extinction phenomenon
among cephalopods.

Why Paleontology?

cales. It elucidates how life has adapted to Earth's evolving

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environments and how these environments have been shapedthe history of life on Earth. It was traditionally focused onby the existence of life, thereby enhancing our understanding“discoveries,” implying that documenting new fossils was a

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currently experiencing the “sixth mass extinction event”. By

paleontology. However, in recent years, the advent of novel

understanding the past mass extinction events, paleontologists

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can offer insights into what we may anticipate in a similar

KDYHVLJQL¿FDQWO\DGYDQFHGWKH¿HOGHYHQWKRXJKWKHGLVFRY-contemporary scenario. This includes determining which spe-

HU\RIQHZIRVVLOVUHPDLQVFUXFLDO)RULQVWDQFHSDOHRQWRORJ\cies are at the highest risk, identifying the ecosystems likely

provides us with the sole direct evidence of the history ofto be most profoundly impacted, and estimating the duration

evolution and the diversity of life across geological times-of potential recovery. The fossil record can supply data on38

白眉プロジェクト 2023

how ecosystems responded to and recovered from past mass

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extinctions. This information can steer modern conservation

an external shell. Although ammonoids were more abundantefforts, assisting us in understanding which strategies areand diverse in the Cretaceous oceans, ammonoids became

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extinct and nautiloids survived. Several hypotheses have beenin constructing models that predict potential outcomes of theproposed to explain the selective extinction and the kill mech-current trends in biodiversity loss.

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H[WLQFWLRQLQFOXGHWKHGL൵HUHQFHLQKDWFKLQJVL]HJHRJUDSKL-Cephalopods

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factor of the selective extinction because it is known that a

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decrease of pH affects the calcification of marine calcifiers

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HJSODQNWLFJDVWURSRGSWHURSRGV2UUHWDO 'HVSLWHWKHUHIRUHIUHTXHQWO\IRXQGLQWKH¿HOG'XHWRWKHLUZRUOGZLGH

DOOWKHK\SRWKHVHVLWZDVGL൶FXOWWRWHVWPRVWRIWKHK\SRWK-distribution, high abundance, and rapid evolutionary rate,

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extinct cephalopods serve as significant model organisms

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for studying various aspects of evolution and paleontology,

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including paleoecology, biostratigraphy, paleobiogeography,DO +RZHYHUWKHGHJUHHWRZKLFKDPPRQRLGVDQGQDX-and diversity reconstruction. Ammonoids thrived for approx-tiloids responded to the change in pH remains uncertain.

LPDWHO\PLOOLRQ\HDUVVXUYLYHGVHYHUDOPDVVH[WLQFWLRQExploring the link between ocean acidification and selective extinction ofcephalopods

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ammonoids with respect to mass extinction events.

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of the Cretaceous. As demonstrated in previous studies, theGHFUHDVHRIS+D൵HFWVWKHFDOFL¿FDWLRQRIPDULQHFDOFL¿HUVThus, my research aims to reconstruct the cephalopod shell
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this research will serve not only to improve our knowledgeof ammonoid paleobiology and reveal the possible cause of
their extinction but they will also yield important information
to better understand evolutionary processes in cephalopods.
This is particularly important in the light of the ongoing ‘sixth
mass extinction’. In addition, this method can also be applied
to other geological time periods, helping to solve further paOHRELRORJLFDOTXHVWLRQVVXFKDVHDUOLHUH[WLQFWLRQHYHQWVDQG
radiations.

Fig. 1. Reconstruction of ammoinoids (right) and nautiloid (left)
at the latest Cretaceous.

References

K-Pg mass extinction event and selective extinction in cephalopods+HQHKDQ 0 HW DO   5DSLG 2FHDQ$FLGLILFDWLRQ DQG3URWUDFWHG(DUWK6\VWHP5HFRYHU\)ROORZHGWKH(QG&UHWDFHRXV&KLF[XOXE,PSDFWProceedings of the National Acade-

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my of Sciences  by an asteroid impact. Although this event, resulting in the2UU-&HWDO  $QWKURSRJHQLF2FHDQ$FLGL¿FDWLRQ

H[WLQFWLRQRIDSSUR[LPDWHO\RIVSHFLHVZDVQRWWKHPRVWRYHUWKH7ZHQW\)LUVW&HQWXU\DQGLWV,PSDFWRQ&DOFLI\LQJ
Organisms, Nature  devastating mass extinction event, it is the most famous massextinction event for the general public due to the demise ofTajika, A., Landman, N. H., Cochran, J. K., Nishida, K.,some famous groups including non-avian dinosaurs. The

Shirai, K., Ishimura, T., Murakami-Sugihara, N., & Sato, K.

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because of its selective nature. An iconic example of selec-

PHWDEROLVPUHVSRQVLEOH"Geology.

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