Trilobites are one of the most diverse and abundant fossil groups from the early Palaeozoic, and as such are useful for answering important questions about early animal evolution, including developmental processes. Ontogenetic information for a large number of trilobite species has been published, but cases where multiple articulated specimens are known across the full range of developmental stages are rare. The early Cambrian (Series 2, Stage 4) Emu Bay Shale biota from Kangaroo Island (South Australia) is numerically dominated by trilobites, particularly articulated specimens of the ellipsocephaloid Estaingia bilobata, which are present in densities of >600 individuals per square metre on certain bedding planes. Here we describe the essentially complete post‐embryonic ontogenetic series of E. bilobata from the Emu Bay Shale, and investigate patterns of growth relating to articulation and segmentation in this early Cambrian arthropod. Estaingia bilobata exhibits the hypoprotomeric mode of growth, with the epimorphic phase (the cessation of trunk segment generation) reached prior to the onset of the holaspid period. The meraspid pygidium had an extended equilibrium period in which anterior segment release into the thorax was matched by subterminal segment generation. Previously undocumented morphological features of E. bilobata, including the hypostome and bispinose pleural tips in holaspides, are also described. The growth characteristics and morphological features of E. bilobata documented herein strengthen close phylogenetic relationships between the Estaingiidae, Ellipsocephalidae and Xystriduridae.

中文翻译：

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南澳大利亚早期寒武纪三叶虫Estaingia bilobata的胚后个体发育：树干发育和系统发育意义

三叶虫是早古生代中种类最多，数量最多的化石群之一，因此对于回答有关早期动物进化（包括发育过程）的重要问题很有用。关于大量三叶虫物种的个体遗传学信息已经发表，但是在整个发育阶段都知道多个关节标本的情况很少见。来自南袋鼠岛（南澳大利亚）的早期寒武纪（系列2，第4阶段）Sha湾页岩生物区系在数量上以三叶虫为主，特别是关节形的椭圆形Estaingia bilobata标本，在某些情况下其密度大于每平方米600个人床上用品飞机。在这里，我们描述了基本上完整的胚胎后个体发育系列。the湾页岩中的E. bilobata，并研究与这种早寒武纪节肢动物的关节运动和节段有关的生长方式。大叶紫丁香（Estaingia bilobata）表现出低蛋白的生长模式，在整las期开始之前就达到了表观生长期（主干段生成的停止）。异位性臀腺具有延长的平衡期，其中前节段释放进入胸腔与子端节段的产生相匹配。的以前没有记录的形态特征E. bilobata，包括在holaspides的hypostome和bispinose胸膜提示，也有所说明。双叶E. bilobata的生长特征和形态特征 本文所述的文献加强了雌蕊科，鳞翅目科和腹足纲科之间的密切的系统发育关系。