A new species of Nanhsiungchelys (Testudines: Cryptodira: Nanhsiungchelyidae) from the Upper Cretaceous of Nanxiong Basin, China, and the role of anterolateral processes on the carapace in drag reduction
A new species of Nanhsiungchelys (Testudines: Cryptodira: Nanhsiungchelyidae) from the Upper Cretaceous of Nanxiong Basin, China, and the role of anterolateral processes on the carapace in drag reduction
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中国南雄盆地上白垩统南雄龟一新种（龟甲目：隐龟亚科：南雄龟科）及其背甲前外侧突起的减阻作用
DOI：
10.1101/2022.09.16.506868
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Ke Y
中科院分区：
文献类型：
--
作者：
Ke Y
南雄龟科是白垩纪时期生活在亚洲和北美的一群大型龟。本文报道了南雄盆地上白垩统南雄chelyids （Nanhsiungchelys yangi sp. nov.）一新种。该标本包括一个保存完好的头骨和下颚，以及甲壳和板的前部。Nanhsiungchelys的诊断特征包括大的整个甲壳长度（~ 55.5 cm），由头骨和外壳表面的凹坑和脊组成的雕塑网络，浅脸颊和颞部边缘，深颈部边缘，以及甲壳上的一对前外侧突。然而，南雄chelys yangi不同于其他种类的南雄chelys主要是有一个三角形的嘴（在背面）和宽的前外侧突在甲壳上。此外，前颌高于宽颌、背侧未见上颌骨、一小部分上颌骨向眶后部和腹侧延伸、顶部大于额部等特征是区分南雄chelys yangi和南雄chelys wuchingensis的有力证据。南雄chelys yangi与南雄chelys wuchingensis系姊妹类群。南雄龟和其他一些南雄龟在甲壳上有明显的前外侧突，这在任何现存的海龟中都没有报道过，可能起到了保护头部的作用。南雄盆地在晚白垩世非常热，因此我们认为南雄chelyids可能将自己浸入泥浆或水中以躲避热量，类似于一些现存的陆龟。如果它们能够游泳，我们对流体流动的计算机模拟表明，前外侧突起可以减少运动时的阻力。
Nanhsiungchelyidae are a group of large turtles that lived in Asia and North America during the Cretaceous. Here we report a new species of nanhsiungchelyid, Nanhsiungchelys yangi sp. nov., from the Upper Cretaceous of Nanxiong Basin, China. The specimen consists of a well-preserved skull and lower jaw, as well as the anterior parts of the carapace and plastron. The diagnostic features of Nanhsiungchelys include a large entire carapace length (∼ 55.5 cm), a network of sculptures consisting of pits and ridges on the surface of the skull and shell, shallow cheek emargination and temporal emargination, deep nuchal emargination, and a pair of anterolateral processes on the carapace. However, Nanhsiungchelys yangi differs from the other species of Nanhsiungchelys mainly in having a triangular-shaped snout (in dorsal view) and wide anterolateral processes on the carapace. Additionally, some other characteristics (eg, the premaxilla is higher than wide, the maxilla is unseen in dorsal views, a small portion of the maxilla extends posterior and ventral of the orbit, and the parietal is bigger than the frontal) are strong evidence to distinguish Nanhsiungchelys yangi from Nanhsiungchelys wuchingensis. A phylogenetic analysis of nanhsiungchelyids places Nanhsiungchelys yangi and Nanhsiungchelys wuchingensis as sister taxa. Nanhsiungchelys yangi and some other nanhsiungchelyids bear distinct anterolateral processes on the carapace, which have not been reported in any extant turtles and may have played a role in protecting the head. The Nanxiong Basin was extremely hot during the Late Cretaceous, and so we suggest that nanhsiungchelyids might have immersed themselves in mud or water to avoid the heat, similar to some extant tortoises. If they were capable of swimming, our computer simulations of fluid flow suggest the anterolateral processes could have reduced drag during locomotion.