Department of Geosciences, Universidad de Los Andes, 111711, Bogotá D.C., Colombia.
College of Resources and Environmental Engineering College, Guizhou University, Guiyang, 550025, China.
Sci Rep. 2020 Aug 24;10(1):14099. doi: 10.1038/s41598-020-70883-5.
The study of moulting behaviour in the fossil record is relatively well known in arthropods and this is especially true for trilobites. Nevertheless, while studies focusing on the style of moulting in social and semi-social groups of modern animals (e.g. arthropods) are common, very few works investigate moulting adaptations in deep time. Here we report a trilobite assemblage from the Cambrian Series 2 "Tsinghsutung" Formation of South China. Around 850 specimens were used for this study from three different levels across one section near Balang (SE Guizhou Province, South China). These levels preserve numerous trilobite clusters in some cases containing around 400 individual specimens. Up to four species have been found in these clusters, but two species are more common. Trilobite clusters bear a high percentage of disarticulated specimens that we interpret as moults. Additionally, measurements of bioclast orientation and the dorsoventral attitude suggests very quiet water conditions followed by rapid burial events, prior to scavenger disturbance. Together, this indicates that the fossil assemblages were a result of a biological phenomenon rather than mechanical processes, allowing us to interpret the position of the fossil parts as different moulting configurations. Since the trilobite assemblage seems to be in situ, the large number of exuviae suggests a local place of migration. This was triggered by the need for group protection while moulting, which is suggestive of gregarious behaviour, possibly synchronized. These trilobites from the Cambrian Epoch 2, Age 4 constitute one of the earliest known gregarious community of trilobites and has important implications for understanding the ecology of this group during their emergence in the Cambrian.
化石化石记录中蜕皮行为的研究在节肢动物中相对较为知名，三叶虫尤其如此。然而，尽管研究集中在现代动物（例如节肢动物）的社会和半社会群体的蜕皮方式上，但很少有研究调查深时的蜕皮适应。在这里，我们报告了来自华南寒武纪第 2 期“澄江组”地层的三叶虫组合。来自贵州东南部巴郎附近一个剖面的三个不同层位，共使用了约 850 个标本进行研究。这些层位在某些情况下保存了许多三叶虫集群，其中包含约 400 个个体标本。在这些集群中发现了多达四个物种，但两个物种更为常见。三叶虫集群中保存了大量的分离标本，我们将其解释为蜕皮。此外，生物碎屑的定向测量和背腹方向表明，在被食腐动物干扰之前，水非常平静，随后发生了快速埋藏事件。这些共同表明，化石组合是生物现象的结果，而不是机械过程，这使我们能够将化石部分的位置解释为不同的蜕皮配置。由于三叶虫组合似乎是原地保存的，大量的蜕壳表明存在一个局部的迁移地点。这种迁移是由蜕皮时群体保护的需要引发的，这表明了群居行为，可能是同步的。这些来自寒武纪第 2 期、年龄为 4 亿年的三叶虫是已知最早的群居三叶虫社区之一，对理解它们在寒武纪出现时的生态具有重要意义。
