Glycymeris rotunda (DUNKER) の2, 3の化石個体群の相対成長変異

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タイトル別名
  • All ometric variation of some fossil populations of Glycymeris rotunda (DUNKER)
  • Glycymerisrotunda DUNKER ノ 2 , 3 ノ カセキ コタイグン ノ ソウタイ セイチョウ ヘンイ

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説明

This paper deals with a biometrical study on some fossil samples of Glycymeris rotunda (DUNKER), in which the non-sex-associated continuous variation is analyzed from the standpoint of allometry. The material was collected from the Upper Pliocene (Kechienjian stage) of the Kakegawa district and the Pleistocene of the Jizodo district. Postmortem movement of shells at the locality 4, Kakegawa district is evaluated on the basis of the fossil assemblages and also the preservation of the individuals. As the result it is concluded that their transportation may be regarded as being insignificant. Therefore, a biometrical analysis can be based on this para-autochthonous material. The population structure of glycymerid fossils was analyzed in regards to two indices; one is the simple ratio between two measurements, and the other is the diagonal distance from the reduced major axis on a double logarithmic scatter diagram, which represents the equation of average allometry for each sample. The simple ratio between the length of the dental plate measured from the umbo to the anterior extremity and that measured from the umbo to the posterior extremity changes through the growth of the organism. Consequently, the frequency distribution of this index seems to be much influenced by・ the age distribution in sample. On the other hand, the allometric variation with diagonal distance must be less influenced by the sample heterogeneity. The result of chi square test for the frequency distribution of diagonal distance supports the null hypothesis of a normal distribution. The frequency distribution of diagonal distance is always less skewed and less platykurtic than that of simple ratio, as indicated by the coefficients of skewness and kurtosis. Compared with two fossil populations of Kakegawa district and a fossil population of Jizodo district at the relative site of beak, fairly significant difference is found between the allometric equations of the two Kakegawa samples. In this character the Jizodo sample seems to lie between the two. The analysis of isometric variation with simple ratio is so much influenced by the sample contigency and heterogeneity that statistical discrimination or identification of samples could not be made on the basis of this index.

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