Functional Morphology And Quantitative Ontogenetic Study On Cambrian Eocrinoids From The Balang Formation

Balang fauna is yielded in the upper part of the Balang Formation.It is characterized by the fossil assemblages of Redlichiid trilobites and eocrinoids: Protogloboeocrinus yini Zhao et al.,2015 and Guizhoueocrinus yui Zhao et al.,1994,which indicate a special sedimentary environment of outer shelf deep-water facies.As a result,it is important to study the taxonomy,functional morphology and the evolutionary trend of the Cambrian eocrinoids.Based on abundant eocrinoid fossils of Protogloboeocrinus yini Zhao et al.,2015 and Guizhoueocrinus yui Zhao et al.,1994,we study the functional morphology and ontogeny of Cambrian eocrinoids.We summarize the morphological functions in different parts in eocrinoids.Brachioles are the feeding structure of the eocrinoids.Theca is the most important organ,which contains internal organs that for nutrition and respiration.Holdfast contians stem and disc,which is used to adhere on the hard ground or some bio-debris.Taking Guizhoueocrinus yui as a proxy,we use traditional morphometric method and geometric morphometric method to study the morphological changing trend during eocrinoids‘ life history.The result shows that Guizhoueocrinus yui grows continiously in general.However,in some certain structures,it shows a step-wise growth pattern.And we calculated the surface area and the volume of the thecal,as well as the surface area of epispires of Guizhoueocrinus yui,and we finally build a mathmetical funtion to illustrate the respiretory strategy in early eocrinoids.Comparing with two species Globoeocrinus globulus and Sinoeocrinus lui from the Kaili Formation,we find a unique evolutionary trend in thecal morphology,which may indicate an evolutionary divergence in the thecal form of the eocrinoids in Cambrian Series 2 and Series 3.In general,based on quantitative analysis,we suggest a new ontogenetic growth pattern and a mathematical function on respiratory strategy in Cambrian eocrinoids from the Balang Formation.According to the morphological comparison on thecal form between the eocrinoids from the Balang Formation and the Kaili Formation,we reveal the unique evolutionary trend in Cambrian eocrinoids.