Precambrian animal life: Probable developmental and adult cnidarian forms from Southwest china
Precambrian animal life: Probable developmental and adult cnidarian forms from Southwest china
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DOI：
10.1006/dbio.2002.0714
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发表时间：
2002-08-01
影响因子：
2.7
通讯作者：
Davidson, EH
中科院分区：
文献类型：
--
作者：
Chen, JY;Oliveri, P;Davidson, EH
在寒武纪之前，由于在下寒武统化石组合中发现了各自的冠群代表，因此，从遥远的后生动物祖先进化而来的西尼达人和双边人血统的进化分歧发生在寒武纪之前的未知深度。本文报道了来自西南中国前寒武纪磷岩矿床的各种可能的胚胎、幼体和成体微体化石，它们可能比寒武纪辐射早2500万年-4500万年。这些很可能是西尼达人的亲缘关系。显微镜下可见大量早期浮萍状幼虫的切片化石。尽管存在几种形式，但大多数都表现出显著的一致性，这与另一种说法不一致，即它们是人工矿物包裹体。其中一些化石被保存在如此高的分辨率下，以至于可以分辨出单个细胞。我们详细地证实了早先的报道，即在已灭绝的冠群珊瑚虫形式的同一沉积物中存在平板藻类。其他部分揭示了与现代珊瑚底部部分最相似的结构。还观察到了大量类似于现代水生动物原肠动物的化石。这些细胞在形态上再次表现出很好的一致性。虽然只有一个例子，但也展示了一种与现代成体水生动物极其相似的微型动物。综上所述，本文报道的新观察结果表明，早在寒武纪演化事件之前，就存在着多样化的、已经分化的西尼迪亚动物群。由此推论，至少在这个时候，一定也有干群的双边生物。(C)2002年埃尔塞维尔科学公司(美国)。
The evolutionary divergence of cnidarian and bilaterian lineages from their remote metazoan ancestor occurred at an unknown depth in time before the Cambrian, since crown group representatives of each are found in Lower Cambrian fossil assemblages. We report here a variety of putative embryonic, larval, and adult microfossils deriving from Precambrian phosphorite deposits of Southwest China, which may predate the Cambrian radiation by 25-45 million years. These are most probably of cnidarian affinity. Large numbers of fossilized early planula-like larvae were observed under the microscope in sections. Though several forms are represented, the majority display remarkable conformity, which is inconsistent with the alternative that they are artifactual mineral inclusions. Some of these fossils are preserved in such high resolution that individual cells can be discerned. We confirm in detail an earlier report of the presence in the same deposits of tabulates, an extinct crown group anthozoan form. Other sections reveal structures that most closely resemble sections of basal modern corals. A large number of fossils similar to modern hydrozoan gastrulae were also observed. These again displayed great morphological consistency. Though only a single example is available, a microscopic animal remarkably similar to a modern adult hydrozoan is also presented. Taken together, the new observations reported in this paper indicate the existence of a diverse and already differentiated cnidarian fauna, long before the Cambrian evolutionary event. It follows that at least stem group bilaterians must also have been present at this time. (C) 2002 Elsevier Science (USA).