Adaptive strategy of the Late Cretaceous ammonites inhabited offshite waters.

在Obira、Oyubari和其他一些地区获得了许多具有详细地层记录的Desmocerar属和Tragodesmoceroides（软体动物，ammono总科）标本，它们分别属于Cenemanian和Turonian（白垩纪）。首先做了横切面和切向切片，并对所有种群样本中控制形态的主要性状进行了相对生长分析。在种群概念的基础上，通过生物统计学处理，明确了各地区各物种各字符集的时渐曲线。这些年代线被认为是形态演化的基本模式，因为每个特征的地理变异不大，这些数据来自地理分布的主要区域。这些分析结果使我得出结论，Turonian Tragodesmoceroides亚共状态是由Cenomanian Desmovers japonicum演变而来的，只是表面纹饰的变化。在切曼尼亚和图罗尼亚之间的边界上，这种种系的形成在地质上是瞬间发生的。日本菊的形态在物种存续期间是稳态的。turonian tragodesmoceroides subcostatus被认为是该时代的唯一物种。1 .在栖息地分离方面，在中Turonian结束时澄清了这一物种。新定种的物种只出现在较浅的相中。这两个种在整个过程中表现出形态稳态，地理物种的形成是瞬间发生的。

Many specimens of Genus Desmocerar and Tragodesmoceroides(Mollusca,Ammonoidea) which range the Cenemanian and the Turonian(Cretaceous) respectively were obtained from the Obira, The Oyubari and some other additional aread with detailed stratigraphic records.The cross and the tangential sections were at first made, and relative growth analyses were carried out for all population samples on some main characters which controll the morphology. The chronocline of each characters-set is mode clear for each species in each area through the biostatistical traatment on the basis of popuation concept. These chronoclines are regarded to be the essential pattern of the morphological evolution because the geographic variation of each character is not large and these data are obtained from the main area of the geographical distribution.These analytical results leas me to the conclustion that the Turonian Tragodesmoceroides subcostatus evolve from the Cenomanian Desmovers japonicum only with ther change of the surface ornamentation. This phyletic speciation proceeded in a geologically instantaneous time at the boundary between the cemomanian and the Turoniam. The morphology of D. japonicum is homeostatic through the duration of the species.The tTuronian tragodesmoceroides subcostatus is believes to be ont species in the age. I. clatified that is speciatrd by the end oft the middle Turonian in terms of the habitat segregation. The newly speciated speceis exclusibely occurs in somewhat shallower facies. Again these two speicies of Tragodesmocetoides show motphological homeostasis throught the duration, and the geographic speciation took place instantaneously.