Hopkins Melanie J, Chen Feiyang, Hu Shixue, Zhang Zhifei
Division of Paleontology, American Museum of Natural History, New York, New York, United States of America.
Early Life Institute, State Key Laboratory of Continental Dynamics and Department of Geology, Northwest University, Xi'an, China.
PLoS One. 2017 Sep 21;12(9):e0184982. doi: 10.1371/journal.pone.0184982. eCollection 2017.
The early Cambrian Guanshan biota of eastern Yunnan, China, contains exceptionally preserved animals and algae. Most diverse and abundant are the arthropods, of which there are at least 11 species of trilobites represented by numerous specimens. Many trilobite specimens show soft-body preservation via iron oxide pseudomorphs of pyrite replacement. Here we describe digestive structures from two species of trilobite, Palaeolenus lantenoisi and Redlichia mansuyi. Multiple specimens of both species contain the preserved remains of an expanded stomach region (a "crop") under the glabella, a structure which has not been observed in trilobites this old, despite numerous examples of trilobite gut traces from other Cambrian Lagerstätten. In addition, at least one specimen of Palaeolenus lantenoisi shows the preservation of an unusual combination of digestive structures: a crop and paired digestive glands along the alimentary tract. This combination of digestive structures has also never been observed in trilobites this old, and is rare in general, with prior evidence of it from one juvenile trilobite specimen from the late Cambrian Orsten fauna of Sweden and possibly one adult trilobite specimen from the Early Ordovician Fezouata Lagerstätte. The variation in the fidelity of preservation of digestive structures within and across different Lagerstätten may be due to variation in the type, quality, and point of digestion of food among specimens in addition to differences in mode of preservation. The presence and combination of these digestive features in the Guanshan trilobites contradicts current models of how the trilobite digestive system was structured and evolved over time. Most notably, the crop is not a derived structure as previously proposed, although it is possible that the relative size of the crop increased over the evolutionary history of the clade.
中国云南东部早寒武世的关山生物群包含保存异常完好的动物和藻类。节肢动物最为多样且数量丰富，其中至少有11种三叶虫，有大量标本代表。许多三叶虫标本通过黄铁矿置换的氧化铁假象显示出软躯体保存。在此我们描述了两种三叶虫——兰氏古莱得利基虫（Palaeolenus lantenoisi）和曼氏莱德利基虫（Redlichia mansuyi）的消化结构。这两种三叶虫的多个标本都保存有位于头鞍下方扩张的胃部区域（“嗉囊”）的遗迹，尽管在其他寒武纪化石库中有大量三叶虫肠道痕迹的例子，但这种结构在如此古老的三叶虫中尚未被观察到。此外，至少有一个兰氏古莱得利基虫标本显示出一种不同寻常的消化结构组合的保存情况：一个嗉囊以及沿消化道分布的成对消化腺。这种消化结构组合在如此古老的三叶虫中也从未被观察到，总体上很罕见，此前仅在来自瑞典晚寒武世奥斯坦动物群的一个幼年三叶虫标本以及可能来自早奥陶世费祖阿塔化石库的一个成年三叶虫标本中有相关证据。不同化石库内部和之间消化结构保存保真度的差异可能是由于标本之间食物类型、质量和消化点的差异以及保存方式的不同。关山三叶虫中这些消化特征的存在和组合与当前关于三叶虫消化系统如何随时间构建和演化的模型相矛盾。最值得注意的是，嗉囊并非如先前所提出的那样是一种衍生结构，尽管嗉囊的相对大小在该类群的进化历史中可能有所增加。
