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Byeoljubuchelys yeosuensis
Kim, J. Jung, Joyce, Park, H.-Y. Jung, Jo & Huh, 2025
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Abstract
Here, we present a new Cretaceous carettochelyid turtle, Byeoljubuchelys yeosuensis gen. et sp. nov., from the Lower Cretaceous Hasandong Formation of Yeosu, Korea. A nearly complete shell and select elements of the girdles and limbs provide crucial insight into the evolution and aquatic adaptation of this family. Phylogenetic analyses place Byeoljubuchelys yeosuensis at the most basal position within Carettochelyidae. The mid-sized plastron of Byeoljubuchelys yeosuensis appears to be plesiomorphic for the group. The expansion of the plastron during carettochelyid evolution, especially during the Paleogene, may be an evolutionary response to increasing body size or the threat of mammalian predators. Although the shell of Byeoljubuchelys yeosuensis lacks distinct scute sulci, traces are apparent that are reminiscent of juvenile scutes in the extant Carettochelys insculpta, suggesting that scute loss was facilitated in trionychian evolution through the thickening of the epidermis. Byeoljubuchelys yeosuensis possesses a plesiomorphic humerus with a proximally located lateral process and a sigmoidal shaft lacking torsion, implying rowing locomotion rather than the underwater flapping seen in more recent carettochelyids. The repeated acquisition of a softshell in two clades of trionychians during the mid-Cretaceous may be related to an environmental shift towards humid climates at that time, perhaps reflecting a remarkable adaptation to freshwater ecosystems.
Keywords: Byeoljubuchelys yeosuensis, Early Cretaceous, Hasandong formation, Korea, Carettochelyidae, Paleoecology, Micro-CT
Systematic paleontology
Testudines Batsch, 1788
Cryptodira Cope, 1868
Trionychia Hummel, 1929
Carettochelyidae Gill, 1889
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Geographical and geological settings of the type locality of Byeoljubuchelys yeosuensis gen. et sp. nov.
A, Geographical map of South Korea. B, Geological map of Gyeongsang Basin in South Korea. C, Geological map of Gwangyang Bay. D, Aerial photograph of Soneuk Island with adjacent islands. E, Photographs of the holotype in situ. The red asterisks indicate fossil locality |
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Byeoljubuchelys yeosuensis gen. et sp. nov.
Photographs (A, C) and micro-CT generated three-dimensional models (B, D) of the holotype [KDRC-YS-SR-001]
A, B, shell in dorsal view. C, D, shell in ventral view.
Abbreviations: co, costal; ent, entoplastron; epi, epiplastron; hyo, hyoplastron; hypo, hypoplastron; nc, nuchal; ne, neural; pe, peripheral; py, pygal; spy, suprapygal; xip, xiphiplastron |
Byeoljubuchelys yeosuensis gen. et sp. nov.
Diagnosis—Byeoljubuchelys yeosuensis can be diagnosed as a member of Carettochelyidae by the presence of 10 pairs of peripherals, a single, triangular suprapygal, a thickened pygal with an anterior groove, plastral kinesis, a triangular entoplastron, and the absence of plastral scutes. It differs from other carettochelyids by the unique combination of the following characters: neurals and pygal lacking midline keel, neural series broad and continuous, a reversal of neural orientation at neural II, vermiculated peripheral ornamentation, absence of distinct carapacial scute sulci, a lack of paired nuchal processes, a relatively broad cruciform plastron, long cervical vertebrae, and a humerus with sigmoidal shaft and lateral and medial processes at the level of the humeral head.
Type Locality and Horizon—Soneuk Island, Yeosu, Republic of Korea, near the Aptian/Albian boundary, Early Cretaceous.
Etymology—The genus name ‘Byeoljubuchelys’ is derived from the combination of the Korean word ‘Byeoljubu’, a turtle character in Sugungga, one of the epic tales of Pansori (a traditional Korean musical storytelling art), and the Ancient Greek word ‘chelys’ meaning turtle. The species name ‘yeosuensis’ is derived from Yeosu City, where the fossil was found.
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The peripherals and pygal of KDRC-YS-SR-001, holotype of Byeoljubuchelys yeosuensis gen. et sp. nov.
Interpretive drawing of carapace in dorsal view and micro-CT generated three-dimensional models of peripherals in dorsal and posterior view. Dotted lines express the reconstructed outline of peripherals and pygal. pe, peripheral |
Minguk Kim, Jongyun Jung, Walter G. Joyce, Jae-Il Park, Hye-Yeon Jung, Hyemin Jo and Min Huh. 2025. A New, Early Cretaceous carettochelyid Turtle from South Korea provides insights into Softshell Evolution and Aquatic Ecology.
Swiss Journal of Palaeontology. 144, 75. DOI:
doi.org/10.1186/s13358-025-00415-z [08 December 2025]
