Xiao S, Yuan X, Knoll A H
Department of Geology, Tulane University, New Orleans, LA 70118, USA.
Proc Natl Acad Sci U S A. 2000 Dec 5;97(25):13684-9. doi: 10.1073/pnas.250491697.
Phosphatic sedimentary rocks preserve a record of early animal life different from and complementary to that provided by Ediacaran fossils in terminal Proterozoic sandstones and shales. Phosphorites of the Doushantuo Formation, South China, contain eggs, egg cases, and stereoblastulae that document animals of unspecified phylogenetic position; small fossils containing putative spicules may specifically record the presence of sponges. Microfossils recently interpreted as the preserved gastrulae of cnidarian and bilaterian metazoans can alternatively be interpreted as conventional algal cysts and/or egg cases modified by diagenetic processes known to have had a pervasive influence on Doushantuo phosphorites. Regardless of this interpretation, evidence for Doushantuo eumetazoans is provided by millimeter-scale tubes that display tabulation and apical budding characteristic of some Cnidaria, especially the extinct tabulates. Like some Ediacaran remains, these small, benthic, colonial fossils may represent stem-group eumetazoans or stem-group cnidarians that lived in the late Proterozoic ocean.
磷质沉积岩保存了早期动物生命的记录,这与元古宙末期砂岩和页岩中的埃迪卡拉纪化石所提供的记录不同且互为补充。中国南方陡山沱组的磷块岩含有卵、卵壳和实心囊胚,这些记录了未明确系统发育位置的动物;含有假定骨针的小化石可能专门记录了海绵的存在。最近被解释为刺胞动物和两侧对称后生动物保存下来的原肠胚的微化石,也可以解释为传统的藻类囊肿和/或因成岩作用而改变的卵壳,而成岩作用已被证明对陡山沱磷块岩有广泛影响。不管这种解释如何,陡山沱真后生动物的证据由毫米级的管道提供,这些管道显示出一些刺胞动物(特别是已灭绝的表珊瑚目)特有的隔板排列和顶端出芽。像一些埃迪卡拉纪遗迹一样,这些小型、底栖、群体化石可能代表生活在元古宙晚期海洋中的干群真后生动物或干群刺胞动物。