Beyond the Burgess Shale: Cambrian microfossils track the rise and fall of hallucigeniid lobopodians
Beyond the Burgess Shale: Cambrian microfossils track the rise and fall of hallucigeniid lobopodians
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DOI：
10.1098/rspb.2013.1613
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发表时间：
2013-09-22
影响因子：
4.7
通讯作者：
Harvey, Thomas H. P.
中科院分区：
文献类型：
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作者：
Caron, Jean-Bernard;Smith, Martin R.;Harvey, Thomas H. P.
伯吉斯页岩型矿床以其保存完好的软体生物而闻名，代表了寒武纪“大爆发”期间进化的一系列动物体结构。然而，这些化石沉积物的稀有性使得重建其组成生物的更广泛分布变得困难。相比之下，微观骨骼元素代表了早期动物进化的广泛编年史，但在没有相应的全身化石的情况下很难解释。在这里，我们提供了对来自伯吉斯页岩（寒武纪系列 3，第 5 阶段）的寒武纪叶足类（泛节肢动物）蠕虫 Hallucigenia sparsa 背刺的新观察结果。这些化石表现出独特的鳞片状微结构和层状（锥中锥）结构，共同识别出迄今为止神秘的碳质和磷酸盐寒武纪微化石（包括蒙古石管、Rushtonites 和菱角角化石的材料），作为迷幻类叶足动物的脊柱。因此，Hallucogeniids被揭示为从Terreneuvian晚期（寒武纪第2阶段）到寒武纪“中期”（系列3）的不同寒武纪群落的重要且广泛的组成部分；它们在寒武纪末期的明显衰退可能部分是由埋藏学造成的。致幻类骨片的锥中锥结构与现代有甲动物的硬化角质层结构（颚和爪）相同。更一般地说，我们的结果强调了伯吉斯页岩型化石和孤立的微化石在记录早期动物进化方面的相互重要性和互补作用。
Burgess Shale-type deposits are renowned for their exquisite preservation of soft-bodied organisms, representing a range of animal body plans that evolved during the Cambrian 'explosion'. However, the rarity of these fossil deposits makes it difficult to reconstruct the broader-scale distributions of their constituent organisms. By contrast, microscopic skeletal elements represent an extensive chronicle of early animal evolution-but are difficult to interpret in the absence of corresponding whole-body fossils. Here, we provide new observations on the dorsal spines of the Cambrian lobopodian (panarthropod) worm Hallucigenia sparsa from the Burgess Shale (Cambrian Series 3, Stage 5). These exhibit a distinctive scaly microstructure and layered (cone-in-cone) construction that together identify a hitherto enigmatic suite of carbonaceous and phosphatic Cambrian microfossils-including material attributed to Mongolitubulus, Rushtonites and Rhombocorniculum-as spines of Hallucigenia-type lobopodians. Hallucigeniids are thus revealed as an important and widespread component of disparate Cambrian communities from late in the Terreneuvian (Cambrian Stage 2) through the 'middle' Cambrian (Series 3); their apparent decline in the latest Cambrian may be partly taphonomic. The cone-in-cone construction of hallucigeniid sclerites is shared with the sclerotized cuticular structures (jaws and claws) in modern onychophorans. More generally, our results emphasize the reciprocal importance and complementary roles of Burgess Shale-type fossils and isolated microfossils in documenting early animal evolution.