Resolution of the earliest metazoan record: Differential taphonomy of Ediacaran and Paleozoic fossil molds and casts
Resolution of the earliest metazoan record: Differential taphonomy of Ediacaran and Paleozoic fossil molds and casts
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DOI：
10.1016/j.palaeo.2018.11.009
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发表时间：
2019
期刊：
影响因子：
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通讯作者：
B. A. MacGabhann;J. Schiffbauer;J. Hagadorn;P. Van Roy;E. Lynch;L. Morrison;J. Murray
中科院分区：
文献类型：
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作者：
B. A. MacGabhann;J. Schiffbauer;J. Hagadorn;P. Van Roy;E. Lynch;L. Morrison;J. Murray
我们对早期后生动物演化的认识大多来自埃迪卡拉纪碎屑沉积岩中未矿化的死亡面具或内浮雕模和铸件化石。这一记录通常被认为是一个独特的“埃迪卡拉时代的埋藏窗口”，然而，在古生代碎屑岩中的软体模具和铸件的流行一直在增加，乞求扩展，或修改，我们的理解，这是一个古老的主题。这些化石中最主要的是eldonids，一个非生物矿化的茎后口动物群。由于eldonids也保存为压缩或扁平的化石从像伯吉斯页岩，澄江和凯里的存款，他们提供了一个比较的案例研究，以评估在此期间的模具/铸造式保存的埋藏保真度。EDS和拉曼显微光谱分析的奥陶纪和泥盆纪eldonid模具和铸件，并与伯吉斯页岩eldonids的比较，表明模具/铸造埋藏风格产生显着较低的保真度的化石保存。我们建议，eldonid模具/铸造化石保存的还原铁离子的吸附到主要由高分子量（HMW）的生物聚合物，需要酶降解之前腐烂的组织。在这些吸附的离子周围的铝硅酸盐和/或硫化物的成核和生长形成了可结晶的表面饰面，保留了死亡面具模具。更不稳定的组织不能在这种模具和铸造方式中被固定。来自南澳、俄罗斯白色海地区、纳米比亚和纽芬兰的埃迪卡拉纪铸模和铸件化石显示出与这一新提出的模型一致的演化特征。对其保存模式的分析表明，第一代后生动物缺乏高分子量生物聚合物组织，不可能以这种特定的方式形成化石。因此，了解后生动物的起源和最早的进化需要关注其他模式的进化。
Much of our knowledge of early metazoan evolution is derived from unmineralized death mask or endorelief mold and cast fossils in Ediacaran clastic sedimentary rocks. This record is often regarded as a unique ‘Ediacaran taphonomic window’; however, the prevalence of soft-bodied molds and casts in Paleozoic clastic rocks has been increasing, begging an extension, or modification, to our understanding of this preservational motif. Chief amongst such fossils are eldonids, a non-biomineralized group of stem deuterostomes. Because eldonids are also preserved as compressed or flattened fossils from deposits like the Burgess Shale, Chengjiang and Kaili, they offer a comparative case study for evaluating the taphonomic fidelity of mold/cast-style preservation during this interval. EDS and Raman microspectroscopic analysis of Ordovician and Devonian eldonid molds and casts, and comparison with Burgess Shale eldonids, suggests the mold/cast taphonomic style produces significantly lower fidelity of fossil preservation. We propose that eldonid mold/cast fossils are preserved by the adsorption of reduced iron ions onto tissues composed primarily of high molecular weight (HMW) biopolymers which require enzymatic degradation prior to decay. Nucleation and growth of aluminosilicates and/or sulfides around these adsorbed ions forms a fossilizable surface veneer, preserving a death mask mold. More labile tissues could not be fossilized in this mold and cast style. Ediacaran mold and cast fossils from South Australia, the White Sea region of Russia, Namibia, and Newfoundland exhibit preservational characteristics consistent with this new proposed model. Analysis of their preservational mode suggests that the first metazoans, which would have lacked HMW biopolymeric tissues, could not have been fossilized in this particular style. Thus, understanding the origin and earliest evolution of the Metazoa requires a focus on alternative modes of fossilization.