Based on the predecessors' research results,five criterions to distinguishing and dividing palaeocommunities were proposed: 1) Congener palaeocommunities should be in a same sedimentary environment,and some adjacent palaeocommunities on temporal and spatial distribution should be grown in different physical geography environments;2) The oryctocoenose of palaeocommunity is buried in situ;3) In a same stratigraphic section,the similarity rate of fossil in different horizons of the same palaeocommunities is hi...