The first record of redfieldiiform fish (Actinopterygii) from the Upper Triassic of Korea: Implications for paleobiology and paleobiogeography of Redfieldiiformes
By: Su-Hwan Kim, Yuong-Nam Lee, Jin-Young Park, Sungjin Lee, Hang-Jae Lee
Summarized by: Jonathan Weimar
Jonathan Weimar is a geology major at the University of South Florida. Currently he is a senior and is very interested in space and natural hazards. After he obtains his degree, he plans to research the possible careers that coexist with his interests. Aside from geology, he loves making music and has a dream of becoming a professional music artist.
What data were used? A new well-preserved fossil of redfieldiiform , a type of ray-finned fish, has been discovered from the Triassic Amisan Formation in South Korea. The fossil slightly differs from the regular morphology of redfieldiiform taxa and therefore, represent a new taxon called Hiascoactinus boryeongensis.
Methods: The Amisan Formation reaches depths of up to 1000m thick and is broken up into three different sections: the lower member, the middle member, and the upper member. By looking at the floral assemblage of the Amisan Formation, scientists were able to date the depositional age of these fossils to be of the Late Triassic (about 237 million years ago).
Results: The redfieldiiform fish belongs to the larger group called the ray-finned fishes, which make up the majority of fish in today’s oceans. While there have been many discoveries of the redfieldiiform fish in various continents such as North America and Australia, this is the first valid record of the ray-finned fish in Asia. Even though there have been previous records of the redfieldiiform fish in China, Siberia, and Russia, they have been inaccurate, and therefore the specimen in this article found in Korea is notably the first valid record of redfieldiiform fish in Asia. The redfieldiiform fish has many distinguishable characteristics that include: anal and dorsal fins with membranes between the rays,positioning of the anal and dorsal fins, a single-plated ray, and a spindle shaped body covered with scales. The official name given to the discovered fossil is Hiascoactinus boryeongensis. The genus name“Hiascoactinus” is Greek and Latin- based and refers to the unique dorsal and anal fins, while the species name “boryeongensis” refers to the city of Korea, Boryeong. The fossil has a length of 138mm and a width of 38mm. Almost all of the fossil is intact, except some parts of the caudal fin, furthest from the head, as well as parts of the skull and stomach region. Morphologically, there are differences between the new taxon Hiascoactinus boryeongensis and the redfieldiiform fish that have been scientifically researched. For example, there is a difference that focuses on the dorsal and anal fins of the fish. These fins are what help the fish directionally and are very important. A lot of ray-finned fish erect their fins to quickly get away from predators and go after prey as it helps with turning maneuvers. The dorsal and anal fins of the Hiascoactinus boryeongensis, however, are not fully connected between rays, unlike other closely related fish. This would have made it harder for them to complete turning maneuvers. Because of this, it is suggested that the species was slow swimming predators and went after prey that was inactive.
Why is this study important? This study is important for many reasons. Firstly, this fossil is well-preserved, which means that it has the greatest potential of revealing information about its physiology, morphology, and taxonomy. It allows for the study of the redfieldiiform group and provides information about how this species may have lived million years ago (e.g., the structures of the fins could indicate its swimming capabilities). Lastly, it shows that global sampling of fossils can reveal new evolutionary adaptations and biogeographic patterns of different species.
The big picture: This study provides insight on the redfieldiiform fish and shows us how we can use morphological differences to define a new species. This article also shows us the importance of reevaluation of scientific evidence. The previous records of the ray-finned fish found in Russia and China were inaccurate and provided inaccurate biogeographic information on the redfieldiiform fish record. It was with this study and the well-preserved fossil founded in Korea that shows us the first true record of one of these fish in Asia.
Citation: Kim, S., Park, J., Lee, S., & Lee, H. (2019). The first record of redfieldiiform fish (Actinopterygii) from the Upper Triassic of Korea: Implications for paleobiology and paleobiogeography of Redfieldiiformes. In 1011400475 778507242 Y. Lee (Ed.), Gondwana Research (Vol. 80, pp. 275-284). Amsterdam, Netherlands: Elsevier. doi:https://www.sciencedirect.com/science/article/pii/S1342937X19303211