A new tuna specimen (Genus Auxis) from the Duho Formation (Miocene) of South Korea

  1. Dayun Suh
  2. Su-Hwan Kim
  3. Gi-Soo Nam

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Abstract

A partially preserved caudal vertebrae imprint of a tuna was discovered from the Duho Formation (Miocene) of South Korea. This specimen was assigned to the genus Auxis and represents the second record of fossil Auxis found in South Korea and in the world. We compared the vertebral morphology of the studied specimen to that of currently known species of Auxis , including extinct taxa. However, the specimen could not be assigned to any extant or new species of Auxis due to anatomical differences and a lack of comparability. The discovery of a new specimen of Auxis  aligns with theories of high marine biodiversity in the East Sea (Sea of Japan) and its opening in the Early to Middle Miocene. A widely opened East Sea and upwelling activities might have increased the abundance and diversity of large oceanic fishes such as tunas during the deposition of the Duho Formation. The specimen supports paleoenvironmental interpretations of the Duho Formation as pelagic and subtropical. A taphonomic scenario of the specimen was inferred based on the lack of anal pterygiophores and the leaf imprint on the matrix. The specimen would have been exposed for at least a month in a low-energy sedimentary environment at the deep-sea bottom and would have undergone disintegration before being buried.

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  1. Version published to 10.24072/pcjournal.585
  2. Peer Community in Paleontology

    A newly discovered fossil of a tuna fish from the Miocene has been identified in the Duho Formation in Pohang City, South Korea (Suh et al., 2025). The new find, attributed to the genus Auxis, represents only the second valid fossil record of this genus globally, thus contributing to the understanding of evolutionary history within the Scombridae family (Collette and Nauen, 1983; Nam et al., 2021). 

    The partially skeleton GNUE322001 consists of a few articulated caudal vertebrae preserving diagnostic features of the genus Auxis (Suh et al., 2025). Although it is not possible to compare the new find with the only fossil species known to date, †A. koreanus Nam et al., 2021, the significant difference in size suggests that it could be a different species. The fossil, preserved in fine-grained mudstone, also offers insights into taphonomic processes, suggesting that the specimen underwent significant decomposition in a low-energy sedimentary environment before burial.

    The new record of Auxis supports interpretations of the Duho Formation as a pelagic and subtropical marine habitat, shaped by upwelling activities during the Miocene (Graham and Dickson, 2000; Kim and Paik, 2013; Nam et al., 2021). This discovery emphasizes the significance of upwelling zones in fostering biodiversity and highlights the value of fossil records in reconstructing prehistoric marine ecosystems (Lalli and Parsons, 1997; Wang and Lee, 2019).

    References

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    Kim, J., and Paik, I. S. (2013). Chondrites from the Duho Formation (Miocene) in the Yeonil Group, Pohang Basin, Korea: Occurrences and paleoenvironmental implications. Journal of the Geological Society of Korea, 49(3), 407–416. https://doi.org/10.14770/jgsk.2013.49.3.407

    Lalli, C. M., and Parsons, T. R. (1997). Biological oceanography: An introduction (2nd ed). Butterworth Heinemann.

    Nam, G.-S., Nazarkin, M. V., and Bannikov, A. F. (2021). First discovery of the genus Auxis (Actinopterygii: Scombridae) in the Neogene of South Korea. Bollettino Della Società Paleontologica Italiana, 60(1), 61–67. https://doi.org/10.4435/BSPI.2021.05

    Suh, D., Kim, S.-H., and Nam, G.-S. (2025). A new tuna specimen (Genus Auxis) from the Duho Formation (Miocene) of South Korea. bioRxiv, 605724, ver. 5 peer-reviewed by PCI Paleo. https://doi.org/10.1101/2024.07.29.605724

    Wang, Y.-C., and Lee, M.-A. (2019). Composition and distribution of fish larvae surrounding the upwelling zone in the waters of northeastern Taiwan in summer. Journal of Marine Science and Technology, 27(5), article 8. https://doi.org/10.6119/JMST.201910_27(5).0008

  3. Version published to 10.1101/2024.07.29.605724 on bioRxiv