Study On Brachiopods From Cambrian Jialao Formation In Jianhe,Guizhou

In this paper,the composition,burial characteristics and coevolution of brachiopods from Jialao Formation in the south of Balang Village,Jianhe,Guizhou are studied.Eight species assigned to five genera were identified and described from Jialao Formation,including 1 similar species and 3 indeterminate species.Namely,Nisusia guizhouensis,N.granosa,N.sp.,Diandongia circularis,Prototreta sp.,Acrothele bohemica,Paterina sp.,Pa.cf.zenobia.Among them,Pro.sp.、 A.bohemica、Pa.cf.zenobia were firstly discovered in Jialao Formation of Jianhe.They have not only enriched the brachiopods’ diversity of Jialao Formation,but also broadened the geographical distribution of these genera.Comparing to the assemblage characteristics of brachiopods of the underlying strata,the brachiopods of the Jialao Formation are characterized by high diversity and low abundance.The burial characteristics of brachiopods in Jialao Formation are discussed and found that there were three types of preservation: single shell preservation,double shell preservation and group preservation.Many fragments fossils of multiple phyla such as brachiopods,mollusca,and algae were usually preserved together.Few intact individuals are found and their arrangements are no direction.All these indicate that the seafloor hydrodynamic force was strong at that time,some organisms may have been transported for some distance and then buried.However,a specimen of brachiopods with soft part,a pedicle stretches between two shells,is discovered in Jialao Formation,providing new materials for the study of soft bodies of Cambrian brachiopods.The quantitative morphological study of Nisusia guizhouensis,which was abundant in Jialao Formation,Kaili Formation and Tsinghsutung Formation,the result showed that the cardinal extremities of ventral and dorsal shells get gradually expanded outwards from Tsinghsutung Formation to Jialao Formation.While the anterior of N.guizhouensis shells shrink inward,and the visceral cavity also becomes smaller.These differences of N.guizhouensis in different strata may attribute to the different sedimentary environments,and the changes of shell morphology and characteristics may be the result of adaptation to stronger hydrodynamic environment.This study not only enriches the biological assemblage of Jialao Formation in Jianhe,Guizhou,but also provides new information on its systematic classification and the co-evolution of organisms and environment.