Sessile Epifauna Of Chengjiang Largert(?)tte And Its Origin And Evolution

The Chengjiang Largert?tte represents one of the earliest multicellular faunas on earth since the Phanerozoic eon. It becomes the most excellent window for deciphering the Cambrian explosion because of its abundant fossils and exquisite preserving quality. At present, there are over 180 species of 160 genera in Chengjiang, besides alga, trace fossils and coprolites. It contains almost every primary phyla of protostomes nowadays, more importantly, early representatives of the duterostomes were also found in the largert?tte.The targets of this study are mainly the special group—sessile epifauna. They live on the substrate or on other shells, including: several species of sponge; cnidarians, such as Xianguangia,Archotuba; brachiopods as Longtancunella,Xishanella,Kutorgina,Diandongia; some problematica such as chancelloriids; Cotyledion tylode; Phlogites; Dinomischus; duterostomes as Cheungkangella.The author has done some field investigation and fossil-collection concerning the lower Cambrian strata in Kunming, Yunnan, in order to discuss the origin and evolution of the sessile epifauna. The origin of sessility not only reflects the ecology and living habits of the metazoans, but also has close relationship with the presence of the biomineralized or slerotized. Moreover, it is meaningful for discussing the growing processes and ecology of the planktonic larvae. Most larvae of the sessile epifauna are all pelagic, which reflects their ancestral habit and also has important significance during their later growth and reproduction. The planktonic larva could seek for appropriate substrate actively during its short pelagic period, and make good preparation for later sessile stage.As the study on many specimen of sessile epifauna indicated, most of them prefer to attach to other shells. Now we divide the attaching substrates into two kinds: sclerotized substrates and abiotic substrates. However the former is more advantageous than the latter. The common sclerotized substrates are: trilobite librigena and fixigena, axial spine; brachiopod shells; hyoliths and so on. Cambrian is a significant period for the evolution of sessile epifauna, eyewitnessing the evolution from the only abiotic substrate to the sclerotized substrates, which is also related to the appearance of the abundant biomineralized and slerotized skeleton during Cambrian.The diversification of attachment during early Cambrian plays a great role in the subsequent radiation of metazoan and the ecological diversity. There are three periods of attachment evolution: Ediacaran; Meishucunian; Qiongzhusian.