An ancestral turtle from the Late Triassic of southwestern China
An ancestral turtle from the Late Triassic of southwestern China
复制标题
中国西南部晚三叠世的龟祖先
DOI：
10.1038/nature07533
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发表时间：
2008-11-27
期刊：
影响因子：
64.8
通讯作者：
Zhao, Li-Jun
中科院分区：
文献类型：
--
作者：
Li, Chun;Wu, Xiao-Chun;Zhao, Li-Jun
乌龟身体的起源仍然是爬行动物进化史上最大的谜团之一。海龟的解剖学是高度衍生的，这使得很难建立海龟与其他爬行动物群体的关系。已知最古老的海龟是来自德国晚三叠世的原龟，它有一个完全成形的壳，但没有提供任何关于它起源的线索。在这里，我们描述了一种来自中国的新的2.2亿年前的龟，比原龟属稍老，它记录了壳和相关结构进化的中间步骤。腹侧腹甲发育完全，但背甲仅由神经板组成。背侧肋骨扩张，骨皮缺失。新物种表明，胸甲在甲壳之前进化，甲壳形成的第一步是神经板的骨化和肋骨的加宽。这与现存海龟甲壳形成的早期胚胎阶段相对应，表明龟壳不是由骨皮融合而来的。系统发育分析将新物种定位于所有已知海龟的基础，化石和现存的。产生这些化石的海洋沉积物表明，这种原始海龟居住在海洋或河流三角洲的边缘地区。
The origin of the turtle body plan remains one of the great mysteries of reptile evolution. The anatomy of turtles is highly derived, which renders it difficult to establish the relationships of turtles with other groups of reptiles. The oldest known turtle,Proganochelysfrom the Late Triassic period of Germany, has a fully formed shell and offers no clue as to its origin. Here we describe a new 220-million-year-old turtle from China, somewhat older thanProganochelys, that documents an intermediate step in the evolution of the shell and associated structures. A ventral plastron is fully developed, but the dorsal carapace consists of neural plates only. The dorsal ribs are expanded, and osteoderms are absent. The new species shows that the plastron evolved before the carapace and that the first step of carapace formation is the ossification of the neural plates coupled with a broadening of the ribs. This corresponds to early embryonic stages of carapace formation in extant turtles, and shows that the turtle shell is not derived from a fusion of osteoderms. Phylogenetic analysis places the new species basal to all known turtles, fossil and extant. The marine deposits that yielded the fossils indicate that this primitive turtle inhabited marginal areas of the sea or river deltas.