The Study On Bivalved Arthropods Animals In Niutitang Formation Of Cambrian At Zunyi County,Guizhou Province

In this paper,the bivalved arthropods in the Niutitang Formation of Zunyi area are taken as the object of study.By using Morphometrics,induction deduction method and other methods,the author explains the ontogenesis,composition,migration radiation and burial characteristics of the bivalved arthropods in the Cambrian Series 2 Stage 3 from Zunyi area(shallow water shelf area)。The study shows that there are 4 genus 6 species of biovalved arthropods of the Niutitang Formation in Zunyi county;they are Isoxys minor,Isoxys paradoxus,Isoxys curvirostratus,Perspicaris sp.,Tsunyiella luna and Emeiella venusta.T.luna is the dominant species.The biovalved arthropods of the Chengjiang Fauna are six times more than which in the Niutitang Biota in Zunyi area at the genus level.I.minor.,I.curvirostratus and E.venusta are both found,the closer the chengjiang area,the higher the similarity.On the longitudinal,the composition of large bivalved arthropods is closely related to the environment and evolution stage.The continuity of each species is quite different,such as Isoxys and Tuzoia relatively well,Chuandianella and Pectocaris are relatively poor.The appearing sequence of Perspicaris and Isoxys supports the viewpoint that evolution from Perspicaris to Isoxys.The distribution characteristics of the small bivalved arthropods(Bradoriida)reflect the following characteristics of the early Cambrian Bradoriida: most genera have regional characteristics,have rapid evolution speed,and are greatly affected by the environment;most of them are adapted to the narrow range of water depth environment,such as T.luna,a few of species are different,such as E.venusta.Comprehensive analysis shows that the environment is the main factor which controlling the genus and species distribution of bivalve arthropods during the Cambrian Series 2-3,and the evolution stage also affected the specific genus and species distributionThe ontogeny of Tsunyiella luna of the Cambrian Niutitang Formation,Zunyi,Guizhou province is studied preliminarily here by using geometric morphometric method.The result shows that the growth pattern of T.luna is allometric.And the ratio between the shell height and the shell length decrease during the ontogeny.And the ratio between the hinge-line length and shell length is decreasing with inverse proportional function during the ontogeny.The ventral margin is balanced growth.However,the molting stage is still not clear now.The ontogeny can be divided into three stages: early stage,middle stage and late stage.In the early stage,structure is from scratch,and the ratio of the height to length became larger as the shell become round.In the middle stage,the proportion of anterior node and dorsal margin ridge in the shell and the ratio of height to length gradually decreased,and the mid-dorsal area gradually increased on the contrary and the shell form gradually retral swing.In the late stage,the proportion of anterior node in the shell increased slightly,and the dorsal margin ridge decreased,and the mid-dorsal area is not obvious,and the ratio of height to length increased,and the shell form was more round.The bivalved arthropods in Niutitang biota are nearly autochthonous buried.The no-geologic event burial resulted in preservat rarely the soft body,and the environmental changes led to rapid changes in the biological population,finally forming three fossil combinations.The buried characteristics of bivalved arthropods indicating that the upper part of the water could be normal seawater,and the environment of seabed changes to oxygen-rich from dysoxic.The rapid tectonic movement,the special biological evolution stage and the perferable sedimentary environment of the shallow sea shelf provide a large amount of organic matter and a good preservation environment,and black shale develop widely.This study not only increased the biological information of Niutitang Biota,provided an accurate basis for the identification of Tsunyiella,but also provided fossil evidence for the burial mechanism of this biota,as well as provided materials for the research on the restoration of the paleoecology and paleoenvironment in this area and the origin and evolution of early bivalved arthropods.