Evolutionary morphology of ontogenetic trajectories in ectoconchlete cephalopods

2023 Fiscal Year Final Research Report

• Project/Area Number: 20K04149
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 17050:Biogeosciences-related
• Research Institution: Kyoto University
• Principal Investigator: Ubukata Takao 京都大学, 理学研究科, 教授 (00293598)
• Project Period (FY): 2020-04-01 – 2024-03-31
• Keywords: 頭足類 / アンモノイド / 機能-形態空間解析 / アロメトリー / 理論形態モデル / 個体発生軌道

Outline of Final Research Achievements

I propose a new theoretical morphologic model which mimics allometric shell growth in ammonoids to represent ontogenetic trajectories of morphological traits. I generalized the relationship between the trajectories and hydrostatic and hydrodynamic properties to perform a functional morphospace analysis. Functional landscapes were constructed for a juvenile and a sub-adult growth stages on morphospaces with reference axes representing the allometric coefficients. The analytical results show a trade-off relationship between hydrostatic and hydrodynamic efficiencies in the sub-adult or later stage. As a result of morphometric analyses, actual ammonoids occupy the region in the morphospace where shell shapes more or less meet the requirements of hydrostatic and hydrodynamic efficiencies in the adult stage. This result suggests that a balance between hydrostatic and hydrodynamic efficiencies in the adult stage was important in the macroevolution of ammonoids.

Free Research Field

古生物学

Academic Significance and Societal Importance of the Research Achievements

進化生物学では，成長に伴う形状の変化パターンを変えることなく発生が進んだり遅れたりすることで起こる形態進化が古くから注目されており，異時性と呼ばれている．成功に伴う形状変化の機能的意義を考究した本研究結果は，異時性の解析と親和性があるので，将来的には異時性の進化的意義の理解を深める研究に発展すると期待される．また，本研究では成長に伴う平面巻殻の形状変化を表す数理モデルを開発したが，このモデルは立体巻にバージョンアップすることによって巻貝や二枚貝などに拡大適用が可能となるので，軟体動物の進化形態学に貢献すると期待される．