The Study On Cambrian Echinoderms From The Jindingshan Formation And Gaotai Formation Of Wengan,guizhou Province

The extreme diversity of forms among early echinoderms presents an ideal model for exploring evolutionary dynamics.Determining the relationship between form and function is key to understanding the nature of morphological diversification during evolutionary radiations.Fossils from Jindingshan Formation and Gaotai Formation in Wengan,Guizhou Province enriched the Cambrain echinoderms groups living in shallow water environment,and the preservation of stereomic microstructure of eocrinoids provided key evidence for discussing the morphological function of eocrinoids and the characteristics evolution of early echinoderms.In this paper,the morphology and function of echinoderms are discussed from two aspects.First,according to the previous studies on calcite endoskeleton microstructures of extant echinoderms,this article identified different ring structures and preliminarily analyzed the pore size of stereom in different parts of eocrinoids.Second,from the perspective of macrography characteristics,the morphological functions of echinoderms were quantitatively analyzed by applying the method of computational fluid dynamics(CFD).As the respiratory structure of early eocrinoids,epispire was previously thought to be formed only by soft tissue bulge or depression.However,fossil evidence showed that there are several loosely arranged skeleton plates under the epidermis of epispire.The hydrodynamic performance indicated that the velocity of flow at the convex surface is faster than that of the concave type,which is more conducive to gas exchange.Therefore,it is speculated that the epispire may have a convex form.As the feeding appendages of passive suspension feeding eocrinoids,characteristics of brachiolars had a direct influence on food gathering.Three-dimensional models of the eocrinoids with different shape of brachiolars were used in computer simulations of water flow.The results demonstrate that,different from the previous hypotheses,there is no turbulent vortex around the spiral brachioles.Drag coefficients of Sinoeocrinus lui with straight brachiolars are higher than species with helical type,suggesting the latter were more stable on the sea floor.Compared with these two types,Lyracystis radiata with pinnate brachiolars would create a tighter low-velocity field surrounded brachiolars.The rapid inflow and low-speed outflow of food particles make foods enriched in the brachiolars-enclosed area,which is beneficial to filtering food.Pinnate filter feeding organs also occurred in other biological groups,which may reflect that although suspension feeders evolved a high diversity of groups,sometimes with remarkably convergent morphologies.