澄江化石库中的双胚层动物新知

New diploblasts from Chengjiang fossil lagersttte

作为观察寒武纪大爆发主幕奥秘的最佳科学窗口,澄江化石库展示了三胚层动物(即两侧对称动物)首次全面大辐射的历史产物,让学术界终于看到了已知最古老的同时包括原口类和后口类两大支系的动物谱系庞大“树冠”的主体轮廓,从而给许多较高级动物类群的起源和早期演化研究提供了十分重要的信息。然而,该化石宝库中却很少见到作为“树干”的双胚层动物(即辐射动物)的化石记录,这给“真动物”的源头探秘蒙上了阴影。尽管广布于前寒武纪末期全球浅海域的“文德生物群”一直被认为是动物界早期一次“失败的演化试验”的牺牲品,但其中一支成功延续到早寒武世的春光虫(Stromatoveris)具有叠覆状梳齿构造,很可能代表着栉水母类的一类原始祖先。文中描述新的羽毛状动物王氏澄江海笔(Chengjiangopennawangii)不同于春光虫,前者具有彼此分离的羽枝,且羽枝上保存了排列规整的珊瑚个体虫室,因而与现代八射珊瑚中海笔类的形态学特征十分一致;新的谱系分析显示,它应该代表刺胞动物门中的一个原始类群。

Chengjiang Lagerstatte, is one of the best windows to investigate the main episode of the Cambrian Explosion, yielding numerous diverse well-preserved early triploblastic （Bilateria） soft-bodied fossils. These include the earliest-known representatives of almost all major branches in both the protostomes and deuterostomes, and provide significant information to trace the origins and early evolutions of many ＂advanced＂ animal groups. However, diploblast （Radlata） fossil record in this lagerstatte was rather limited, which would make it very difficult to explore the early evolution of the eumetazoans. Although vendobionts, which widely appeared in the latest Precambrian seas, have been thought the victims in a ＂defeated experiment＂ of early evolutions of animals, one of them survived into the early Cambrian, the frondlike animal Stromatoveris with imbricated comb-like structures, which probably represents the precursor of ctenophores. In this paper we described a new frondose taxon Chengjiangopenna wangii, whose branches are separate and bear regularly-arranged autozooids. These are morphologically strikingly similar to the extant sea-pens of octocorals. A new phylogenetic analysis suggests that this rare early Cambrian anthozoan be among the primitive crown cnidarians.