Verification for the homogeneity of fossil assemblages within the same environment.

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Although an autochtonous fossil assemblage within the same environment has been previously considered to be homogenized due to a time-average process, few has verified it. The species compositions among the three fossil localities (localities 1,2, and 3) are quantitatively compared based on the 979 specimens of twenty-five species in fossilferous silty sands of the inner-shelf facies of the Pliocene Ananai Formation, eastern part of Kochi Prefecture, Pacific-side of southeastern Japan. The three localities are arranged in the same horizon within the 180m distance(1) The most dominant species is Angulus vestarioides in all the localities, the second Nassarius caeratus, the third Fulvia mutica, and the fourth Acila divaricata.(2) In the localities 1 and 2, the fifth dominant species is Oblimopa japonica, whereas Gari anomala is the fifth dominant species in the locality 3.(3) Ammusiopenten praesignis is the sixth dominant species in the localities 1 and 2, but in loclity 3, Paphia sp.is.As a result, the species compositions of the localities 1 and 2 are considered to be nearly homogenized, whereas the remnant locality 3 is considered to be different in the minor species composition.