The first named Ediacaran body fossil, Aspidella terranovica
The first named Ediacaran body fossil, Aspidella terranovica
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DOI：
10.1111/j.0031-0239.2000.00134.x
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发表时间：
2000-07-01
期刊：
影响因子：
2.6
通讯作者：
Anderson, MM
中科院分区：
文献类型：
--
作者：
Gehling, JG;Narbonne, GM;Anderson, MM
1872年，在纽芬兰东部阿瓦隆半岛的新元古代晚期费默斯组（St. John’s Group）中首次发现了terranovica Aspidella Billings，它在地层上比著名的埃迪卡拉生物群高出约1公里，比寒武纪底部低几公里。Aspidella可能比任何其他前寒武纪分类群都得到了更多的重新解释，它被不同地认为是一种软体动物化石或“水母”，一种气体逸出结构，一种固结物或一种机械吸力标记。我们的研究表明，Aspidella包括各种各样的保存形态，从具有凸起边缘和从狭缝辐射的脊的负低浮雕（Aspidella型保存），到具有中心凸台和尖锐外环的平盘（Spriggia保存），再到具有同心装饰的正低浮雕（Ediacaria保存）。标本的大小是连续的，保存方式取决于标本的大小和宿主岩性的粒度；试件的伸长是构造性的。通过观察其复杂的径向和同心纹饰、标本群中相互变形的边界以及与某些独特的埃迪卡拉类群出现在同一层理平面上，证实了Aspidella是一种体化石。Aspidella与全世界新元古代晚期盘状体化石中最常见的几个属难以区分，并且具有优先权。来自澳大利亚的类似化石被解释为叶子状生物的支架。Aspidella床中标本的密度表明，新元古代底栖生物的生物量水平可以与现代海洋生物群落相媲美。与Aspidella有亲缘关系的Palaeopascichnus、Intrites、Neonereites renarius和Yelovichnus系列生长形式被解释为亲缘未知的体化石，而不是痕迹化石。在费默斯组的Aspidella地层中发现了一种新的埃迪卡拉纪三叶躯体化石Triforillonia costellae gen. et sp. nov.。
Aspidella terranovica Billings, 1872 was first described from the late Neoproterozoic Fermeuse Formation (St. John's Group) on the Avalon Peninsula of eastern Newfoundland, approximately 1 km stratigraphically above the famous Ediacaran biota at Mistaken Point, and several kilometres below the base of the Cambrian. Aspidella has been reinterpreted perhaps more than any other Precambrian taxon, and has variously been regarded as a fossil mollusc or 'medusoid', a gas escape structure, a concretion, or a mechanical suction mark. Our studies indicate that Aspidella includes a wide variety of preservational morphs varying from negative hyporeliefs with a raised rim and ridges radiating from a slit (Aspidella-type preservation), to flat discs with a central boss and sharp outer ring (Spriggia preservation), to positive hyporeliefs with concentric ornamentation (Ediacaria preservation). Specimens occur in a continuum of sizes, with preservational styles dependent on the size of the specimen and the grain size of the host lithology; the elongation of specimens is tectonic. Aspidella is confirmed as a body fossil from observations of complex radial and concentric ornamentation, mutually deformed borders in clusters of specimens, and occurrence on the same bedding planes as certain distinctive Ediacaran taxa. Aspidella is indistinguishable from, and has priority over, several of the most common genera of late Neoproterozoic discoidal body fossils worldwide. Similar fossils from Australia are interpreted as holdfasts of frond-like organisms. The density of specimens in the Aspidella beds suggests levels of benthic biomass in the Neoproterozoic that could rival those of modern marine communities. The serial growth forms, Palaeopascichnus, Intrites, Neonereites renarius and Yelovichnus, associated with Aspidella, are interpreted as body fossils of unknown affinities rather than trace fossils. A new, trilobed, Ediacaran body fossil, Triforillonia costellae gen. et sp. nov., is described from the Aspidella beds of the Fermeuse Formation.