Reproductive strategy of basal birds

2022 Fiscal Year Final Research Report

• Project/Area Number: 19K23453
• Research Category: Grant-in-Aid for Research Activity Start-up
• Allocation Type: Multi-year Fund
• Review Section: 0204:Astronomy, earth and planetary science, and related fields
• Research Institution: University of Tsukuba
• Principal Investigator: Tanaka Kohei 筑波大学, 生命環境系, 助教 (50841970)
• Project Period (FY): 2019-08-30 – 2023-03-31
• Keywords: 恐竜類 / 鳥類 / 繁殖 / 卵 / 進化

Outline of Final Research Achievements

This study explores the relative egg size and egg shape of Mesozoic birds to infer the evolution of reproductive strategy in birds. Evolution of egg shape in basal birds was discussed using fossil egg materials collected from the Early Cretaceous of Tamba, Hyogo Prefecture, Japan. These egg specimens are extremely elongated and assigned to a non-avian maniraptoran theropod, suggesting that the drastic change in egg shape occurred after the origin of birds. The relative egg size of basal birds was estimated based on a correlation between pelvis size and egg size of extant species. It can be concluded that non-ornithuromorph birds likely laid small eggs relative to their body size.

Free Research Field

古脊椎動物学

Academic Significance and Societal Importance of the Research Achievements

鳥類は比較的大型の卵を産み，抱卵するなど，独自の繁殖様式を持つ．本研究では，鳥類の繁殖様式がどのように獲得されたのかを，初期鳥類に焦点を当てて考察している．これまで，中生代の鳥類は卵化石に乏しく，詳細な研究は少なかった．そこで本研究では新たな化石試料を見出し，卵形状の進化変遷を考察した．また，骨盤化石から卵サイズを推定する方法を考案することで，卵化石が見つかっていない分類群でも卵サイズの推定が可能となった．凡庸性の高い手法の開発により，今後，鳥類をはじめとする絶滅主竜類の繁殖様式の理解が進むと期待される．