A Study On Representatives Of Problematica (Myllokunmingiids And Chancelloriids) From Early Cambrian Biotas,Eastern Yunnan

Most of the fossils from Chengjiang and Guanshan Biotas are soft-bodied and exceptionally preserved.The former is the main episode of the Cambrian Explosion,while the latter is the extension of the significant event in evolution,which displays the varieties and abundance of the organisms in marine shallow water after Chengjiang.In both biotas,problematica accounts for only a few in total biomass,but it is absolutely indispensable part of the primitive biocenosis.Detailed studies on problematica help reveal the original appearances of the marine organisms and rebuild the marine ecosystem in early Cambrian.Two enigmatic taxa(myllokunmingiids from Chengjiang and chancelloriids from Guanshan)are described and discussed in details herein.Distinguished from those well-preserved specimens of myllokunmingiids in literature,the fossils documented in this thesis are preserved in poor conditions.This non-classic preservation is different from the popular one of being buried alive among Chengjiang fossils.These provide new evidences for investigating the preservation of the Chengjiang fossils in the event mudstone beds.A unique chancellorid from Guanshan Biota,Allonnia tenuis,is described and discussed in details herein.This species is small in size and slender in body profile.The surface and both sides of the stalk are devoid of sclerites,and the lowermost part of the body constricts to a point,all of which are distinguished from those well documented ones.In addition,another metazoan is also described.It shares many characters with Nidelric pugio from Chengjiang Biota,but differences in between help it be erected as a different species.Based on many exceptionally preserved specimens,it is concluded that chancelloriids lead a group-style life and have the ability to compact the body partially or wholly,which might have played a very important role in feeding.Based on the similarities between Nidelric and chancelloriids,it is reasonable to interpret the former as an unusual or even ancestral form of the latter.