New Observation On Oral Structures Of The Vetulicolians From The Early Cambrian Chengjiang Biota

Well-preserved soft-bodied fossils from the Chengjiang biota in Yunnan province have witnessed the main phase of the Cambrian explosion.Up to date,more than280 species were found in the Chengjiang biota,which can be classified into basal animals,protostomes and deuterostomes.One of the most important achievements of Chengjiang biota research is the Phylum Vetulicolia,Subkingdom Deuterostomia,characterized by a bipartite body(pharyngeal region and tail)and five pairs gill slits.The phylum Vetulicolia,with a worldwide distribution,consist of 2 classes(Vetulicolida and Heteromorphida),10 genera,and 17 species.As primitive deuterostomes,related studies of vetulicolians have always attracted the attention of paleontologists.However,the oral morphology and function of vetulicolians hitherto have not been documented,and the relationship between the various genera of vetulicolians is poorly unknown.This research focuses on the evolution of the oral characteristics of the phylum Vetulicolia by means of cladistic analysis and comparative anatomy.The cladistic analysis indicates a step-wise of the evolution of the oral structure of the vetulicolians: Xidazoon type--V.rectangulata type--Vetulicola triangulata sp.nov.type--V.cuneatus type.The Xidazoon type,or double-looped mouth represents the most original type among the phylum Vetulicolia,and then four-lobed mouth type(V.rectangulata).The most specialized type is the four-lobed mouth with unequal size of the dorsal part and ventral part.The mouth of Vetulicola triangulata sp.nov.type represents an intermediate form between that of V.rectangulata and V.cuneatus.