Ecology And Distribution Of The Conodont Merrillina And Hadrodontina From Paleozoic To Mesozoic Boundary

The Permian-Triassic mass extinction was one of the largest extinction event among the five mass extimctions in geological history,the eruption of the great Siberia igneous province associated with global climate oscillation was suggested reponsible for this catastrophic event.As conodonts were successfully survived across P-T Boundary,researches focusing on conodonts is of great significance for understanding the environmental events and paleoenvironmental reconstruction in this period.In this paper,the conodonts family of Ellisonidae,which was rarely noticed during P-T Boundary,was conducted for the identification of multielement apparatus and studied for its environmental distribution.In this paper,four P-T Boundary secion: Gaohua section,Hunan province,Meishan section,Zhejiang Province,Shangsi section,Sichuan Province and Dajiiang section,Guizhou Province were studied for their conodonts mainly in Ellisonidae family.Merrillina ultima was identified in the H.parvus zone from Gaohua section,cili county in hunan province,as well as in Meishan section,Changxing County from zhejiang Province.However,Merrillina ultima was identified in the H.changxingensis Zone from Shangsi section,Guangyuan county in sichuan Province and the multielement apparatus was reconstructed.Parachiognathodus was identified in the H.parvus Zone,Merrillina and Pachycladina was identified in the I.isarcica Zone from Dajiang section,Luodian county in Guizhou Province,and its Multielement apparatus was reconstructed.This is Merrillina's first report in the Triassic period,at the same time,it challenges its previous view of cold water conodonts.In order to further study the distribution characteristics of Ellisonidae,this paper summarized the data of redox conditions of the conodonts and their sedimentary environment.Merrillina ultima was found in dysoxic carbonate platform from Cili county.It was identified in an anoxic shallow marine from Meishan and Shangsi sections,the sedimentary environment in Meishan and Shangsi was shallow water facies and deep water facies.Parachiognathodus is identified in the H.pravus Zone,also in an dysoxic environment.In conclusion,Merrillina and Parachiognathuodus are more distributed in shallow water than deep water,and the conodonts of Ellisonidae have a higher tolerance forthe environment of dysoxic,can appear in the environment of dysoxic and anoxic.Therefore,it can be inferred that the conodonts of Ellisonidae are mostly appear in the shallow water and it have a strong adaptability to the anoxic environment.Although the conodonts of Hadrodontina has not been found in this paper we speculate the possible evolutionary relationship of 3 genera(Ellisonia,Merrillina,Hadrodontina)in Ellisonidae is: the genus Hadrodontina is closer to the conodonts of the genus Ellisonia in morphology,possibly not not evolved from Merrillina as previously suggested by other research.