A taxonomic study for fragmental fossils of Anura from the Lower Cretaceous Sasayama Group

2021 Fiscal Year Final Research Report

• Project/Area Number: 17K18442
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Stratigraphy/Paleontology; Biodiversity/Systematics
• Research Institution: University of Hyogo (2018-2021); The Museum of Nature and Human Activities, Hyogo (2017)
• Principal Investigator: Ikeda Tadahiro 兵庫県立大学, 自然・環境科学研究所, 准教授 (50508455)
• Project Period (FY): 2017-04-01 – 2022-03-31
• Keywords: カエル類 / 化石 / 前期白亜紀 / 篠山層群 / 分類

Outline of Final Research Achievements

Abundant anuran fossils including a few articulated skeletons and numerous fragmentary skeletal elements have been recovered from the Lower Cretaceous Ohyamashimo Formation of the Sasayama Group, Hyogo Prefecture, Japan. The fragmentary skeletal elements have been examined the taxonomic assignments on the basis of the osteological study of extant species and redetermination of detailed characteristics in individual elements of previously reported fossil taxa. As a result, approximately 60% and 30% of these materials were assigned to Hyogobatrachus wadai and Tambabatrachus kawazu, respectively, whereas the other 10% remained unidentified. Moreover, the unidentified remains include two morphotypes of ilium specimens, which exhibited features different from those of described taxa. The results thus suggest that the anuran fauna of the Ohyamashimo Formation consisted at least four taxa, and reveal that the species diversity of the fauna is similar to that of the Early Cretaceous in China.

Free Research Field

古脊椎動物学

Academic Significance and Societal Importance of the Research Achievements

下部白亜系篠山層群大山下層の化石資料は，各分類群の系統進化や古生物地理等を検討する上で極めて重要な資料である．これらの研究において，真の種多様性を評価するためには部分骨など“記載し難い”資料を含め，総合的に検討する必要がある．本研究では，現生種を対象とした包括的な骨学的研究をもとに，カエル類の遊離骨化石を対象にその分類学的帰属を検討した．結果，分類群の決定までには至らなかったが，新たな二タイプの形態型を識別し，同層におけるカエル類相の構成を定量的に明らかにした．今後，本研究を更に発展させることで，同分類群の系統進化や種多様性の変遷，その背後にある古環境等の議論に貢献するであろう．