Systematic Approach To The Community Of The Xiaoshiba Lagerst(?)tte Of The Cambrian Stage 3

The Cambrian,Series 2 is a crucial period for metazoan evolution exhibiting as body-plan radiation and emergence of various phyla.Base on quadrat analysis of some well-preserved specimens of the Xiaoshiba Lagerstatte collected from the lowest part of The Cambrian(Stage 3)Hongjinshao Formation,the author reveals an intermediate link of community succession between the Chengjiang and Guanshan Biotas.The fossils were collected from three sections at the Xiaoshiba,where the thick-bedded sandstone measured from three sections varies in thickness,and overlaying the mudstone of Heilinpu formation.Base on comparison the specimens distributed in the sections,the components of the community may relate to hydrodynamic conditions.The author highlights 5 conclusive points in the thesis as follows:1.The rarefaction curves of the sampling interval were calculated base on specimen density and specimen number.2.The cyclic unit of Hongshiyanaspis zone indicates the water depth reduced as provenance accumulation,which trigger different ecological reaction among four types of functional ecological group:infaunal organisms,such as palaeoscolecidian,were perished;epibenthos sessile and nektobenthos(eg:Pectocaris sp.)were regionally distinct.Conversely,the speciation event of Selkirkia,the prapulid,as well as large-scaling evolutionary trend of fuxianhuiids showing more positive reaction to ecological crisis,both of them are epibenthos vagile.3.With the first appearance of trilobite Zhangshania(marine flooding surface)the components of the Xiaoshiba community changed dramatically.Dioniida fam.nov and other large-sized bivalved arthropods(nektobenthos)occupied the emptying niches.Consider Fuxianhuia xiaoshibaensis is the only boundary crossing taxa yet we known,the succession rate is relatively high within a dozen metres thick stratigraphic sequence.4.Tremendous bioturbation coupling with iron speciation,the proxy of redox data(Fe HR/Fe TOT=0.12-0.20)reveal that the Xiaoshiba Lagerstatte were mostly deposited under an oxic water column.5.The decay experiment of crustaceans under Fe2+ rich condition may help us to reconstruct the decay sequence of some key traits(eyes,head shield)of Fuxianhuia xiaoshibaensis.