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<p>Here, we present a new Cretaceous carettochelyid turtle, <i>Byeoljubuchelys yeosuensis</i> 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 <i>Byeoljubuchelys yeosuensis</i> at the most basal position within <i>Carettochelyidae</i>. The mid-sized plastron of <i>Byeoljubuchelys yeosuensis</i> 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 <i>Byeoljubuchelys yeosuensis</i> lacks distinct scute sulci, traces are apparent that are reminiscent of juvenile scutes in the extant <i>Carettochelys insculpta,</i> suggesting that scute loss was facilitated in trionychian evolution through the thickening of the epidermis. <i>Byeoljubuchelys yeosuensis</i> 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.</p>

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A new, Early Cretaceous carettochelyid turtle from South Korea provides insights into softshell evolution and aquatic ecology

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  • 发表日期：

    2025年12月8日

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  • Minguk Kim,
  • Jongyun Jung,
  • Walter G. Joyce,
  • Jae-Il Park,
  • Hye-Yeon Jung,
  • Hyemin Jo,
  • Min Huh

摘要

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.