Study on the evolution of the wing musculoskeletal system during the dinosaur-bird transition

2021 Fiscal Year Final Research Report

• Project/Area Number: 19K04061
• 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: The University of Tokyo (2020-2021); Institute of Physical and Chemical Research (2019)
• Principal Investigator: Hirasawa Tatsuya 東京大学, 大学院理学系研究科(理学部), 准教授 (60585793)
• Project Period (FY): 2019-04-01 – 2022-03-31
• Keywords: 進化 / 脊椎動物 / 化石 / 恐竜 / 獣脚類 / 中生代 / 進化発生学 / 骨格筋

Outline of Final Research Achievements

The avian wing evolved from the forelimb of ancestral dinosaurs, and a new skeletal muscle, or the "propatagial muscle", spanning between the shoulder and wrirst along its leading edge, was acquired in the evolution of this lineage. In this study, we advanced the understanding of the evolutionary process of the propatagial muscle. First, we found that elbow joint angles preserved in fossils were limited to small values in the presence of the propatagial muscle, and based on this relationship, we analyzed the articulated fossil skeletons, eventually inferring that the propatagial muscle evolved prior to the evolutionary origin of the wing, in the non-avian dinosaurs (maniraptorans). Second, we examined the embryonic development of the chicken, and showed that the propatagial muscle was likely established through a fusion of the shoulder and forearm muscles at the evolutionary origin.

Free Research Field

古生物学

Academic Significance and Societal Importance of the Research Achievements

本研究により、鳥類の翼の筋骨格系進化についての理解が大きく進展した。恐竜から鳥類への移行に関して、単なる骨の形態からの復元ではなく、関節した状態で保存された骨格化石の姿勢（関節角度）を統計学的に比較することで、通常は化石に残らない筋（前翼膜筋）の進化について証拠を得たのは本研究が初である。また、同時並行で進めた発生学研究によって、前翼膜筋がどのように進化したのか解明が進んだが、これは脊椎動物の筋骨格系の進化における制約や方向性を理解していく上で重要な手がかりになると期待される。