先伊迪卡拉期的淮南生物群

在廿世纪中叶以前,人们对于先寒武纪的生物化石发现得很少,除藻类遗迹化石及一些可疑化石外,几乎没有什么可靠的生物化石。与此相反,在古生代地层中,特别是在早寒武世的地层中,却发现了极其丰富的发育较为高级的多门类的生物化石。当时,人们为了解释这种所谓突变现象,就提出了多种假说。但是,在廿世纪中叶以后,随着生产的发展和科学研究的深入,陆续地在晚先寒武纪地层中,发现了许多较大的生物化石、微古植物与微体化石等。由于晚先寒武纪生物化石资料的不断丰富,使得“灾变说”等不攻自破了。

ON THE PRE-EDIACARAN HUAINAN BIOTA

The Huainan Biota named by one of the authors (Zheng, 1980), except for the abundant stromatolites and acritarchs, contains four kinds of the carbonaceous fossils as well: Chuarid, Tawuid, Vendotaenid, and worm fossil. This unique assemblage in late precambrian biosphere so far known is recognized as the oldest one including most abundant and reliable metazoan body fossils. Its isotopic geochroriological data range from 647 to 840 my. Then, the record of the metazoan body fossils is 160 m.y. earlier than that known before.It is of revolutionary significance that there were simply planktonic megafossils in Liulaobei Formation. Among them, the metazoans (worms) were unsegmented or simply segmented, possibly being suspension-feeders. Later, in the Jiuliqiao Formation, the worm diversity increased. The worms characterized by more reeogniznble segment, eoelom and proboscis in some forms were probably deposit-feeders. Especially, the proboscis bolstered the cephalization for the first time. The worms developed the benthonie habit three-dimensionally and acquired the ability to burrow the substrata for their organization streugthed.In accordance with acritarch assemblages, available isotopic geochronological datar and stratigraphic correlation of the biotabearing strata, it is unquestionable that the Huainan Biota was earlier than terminal Prelerozoic glaeiation (Varangian-Laplandian). If so, it would be pre-Bdiacaran (Ediacaran generally ranged from 680 to 570 m.y. ago). It challenged a new traditional opinion that the reliable metazoan body fossils would be discovered only in the strata after the glaciation. The previous ideas about the earliest pathways of animal evolution would have to be revised.