Investigation of sexual dimorphism in fossil organisms

• Project/Area Number: 19K14831
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 17050:Biogeosciences-related
• Research Institution: Okayama University of Science
• Principal Investigator: Chiba Kentaro 岡山理科大学, 生物地球学部, 講師 (80826438)
• Project Period (FY): 2019-04-01 – 2023-03-31
• Project Status: Completed (Fiscal Year 2022)
• Budget Amount: ¥4,160,000 (Direct Cost: ¥3,200,000、Indirect Cost: ¥960,000); Fiscal Year 2021: ¥780,000 (Direct Cost: ¥600,000、Indirect Cost: ¥180,000); Fiscal Year 2020: ¥910,000 (Direct Cost: ¥700,000、Indirect Cost: ¥210,000); Fiscal Year 2019: ¥2,470,000 (Direct Cost: ¥1,900,000、Indirect Cost: ¥570,000)
• Keywords: 恐竜 / 化石 / 古脊椎動物 / 性差 / 骨組織学

Outline of Research at the Start

現生動物の角やとさかには性差が見られることが多い．性差は，主に性選択により発達し，種分化・形態的多様性に深く関連している．一方，化石動物の中にも角やとさかなどを持つものが多くいたが，性差が見出されているものはごく一部で，性差が見られない化石動物では，性選択以外のプロセスでとさかなどの構造が進化したとする仮説が提唱されている．しかし，多くの化石種に性的二型が見られないのは，先行研究の手法的欠陥による可能性が高いと考えられる．そこで本研究では，骨組織学的成長段階推定に基づく，新しい化石種の性的二型評価手法の確立を行う．

Outline of Final Research Achievements

This study investigated methods for distinguishing sexual differences in fossil animals based on osteohistological techniques using ceratopsian dinosaurs, which have prominent ornamentation and are represented by large sample sizes of available specimens. This study suggested that sexual differences might be observed in the ornamentations along with variations in body size in Centrosaurus and Protoceratops. Moreover, through this investigation, several important features in the classification of ceratopsians were identified. While there are many groups of dinosaurs characterized by various ornamentations, the existence of sexual dimorphism has been a matter of debate. In the future, it might be possible to clarify the presence of sexual differences in dinosaurs based on osteohistological investigations.

Academic Significance and Societal Importance of the Research Achievements

現生動物では角やとさか等の構造に性差が見られることが多い。性差は主に性選択により発達し、種分化・形態的多様性に深く関連している。化石動物の中にも同様の装飾構造を持つものが多くいたが，これらの構造に性差が見出されることは極めて稀であり、性選択以外のプロセスでこれらの構造が進化したとする仮説も提唱されている．しかし，本研究の結果骨組織学的に標本の成長段階を推定し、成体個体のみにおいて性差の検討を行うことで、化石種でも性差を認識することができる可能性が示された。これにより、化石種のマクロ進化において見過ごされている性選択の重要性を再評価することが可能となると期待される。

Research Products

• [Journal Article] Taphonomy of a monodominant <i>Gryposaurus</i> sp. bonebed from the Oldman Formation (Campanian) of Alberta, Canada (2022)
  • Author(s): Scott Evan E.、Chiba Kentaro、Fanti Federico、Saylor Beverly Z.、Evans David C.、Ryan Michael J.
  • Journal Title: Canadian Journal of Earth Sciences Volume: 59 Issue: 6 Pages: 389-405
  • DOI: 10.1139/cjes-2020-0200
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Growth variability, dimensional scaling, and the interpretation of osteohistological growth data (2021)
  • Author(s): Cullen Thomas M.、Brown Caleb M.、Chiba Kentaro、Brink Kirstin S.、Makovicky Peter J.、Evans David C.
  • Journal Title: Biology Letters Volume: 17 Issue: 11
  • DOI: 10.1098/rsbl.2021.0383
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Presentation] TAXONOMIC RE-EVALUATION OF PROTOCERATOPS (DINOSAURIA: CERATOPSIA) SPECIMENS FROM UDYN SAYR, MONGOLIA (2020)
  • Author(s): Kentaro Chiba, Michael J. Ryan, Mototaka Saneyoshi, Satoshi Konishi, Yudai Yamamoto, Buuvei Mainbayar, Khishigjav Tsogtbaatar
  • Organizer: Society of Vertebrate Paleontology the 80th Annual Meeting
  • Int'l Joint Research
• [Presentation] New insights on the evolution of the neoceratopsian frill: ornamentations on protoceratops (2019)
  • Author(s): Chiba, K., Ryan, M.J., Yamamoto, Y., Konishi, S., Chinzorig, T., Khatanbaatar, P., Badamkhatan, Z., Saneyoshi, M., and Tsogtbaatar, K.
  • Organizer: Society of Vertebrate Paleontology the 79th Annual Meeting
  • Int'l Joint Research
• [Presentation] A new look at frill ornamentations on Protoceratops and implications for the evolution of neoceratopsian frills (2019)
  • Author(s): Chiba, K., Ryan, M.J., Yamamoto, Y., Konishi, S., Chinzorig, T., Khatanbaatar, P., Badamkhatan, Z., Saneyoshi, M., and Tsogtbaatar, K.
  • Organizer: International Symposium on Asain Dinosaurs
  • Int'l Joint Research