Adaptive strategy of the Late Cretaceous ammonites inhabited offshite waters.

从Obia、Oyubari和其他地区采集了大量的Desmocerar和Tragodesmoceroids(软体动物门，Ammonidae)标本，分别属于塞纳曼和都罗纪(白垩纪)，并有详细的地层记录，首次制作了横切和切向剖面，并对所有种群样本的一些控制形态的主要性状进行了相对生长分析。以种群概念为基础，通过生物统计处理，明确了各区种各性状集的时序模式。这些时间跃层是形态演化的基本模式，因为每个性状的地理变异不大，而这些数据是从地理分布的主要区域获得的。这些分析结果得出结论，都灵类的亚群落地位是从Cenomania Desmovers Japan onicum进化而来的，只是表面纹饰的变化。在地质学上的瞬间，这种物种形成在Cemomania和Turoniam之间的边界上进行。日本血吸虫的形态在整个种群的发育过程中是动态平衡的，其亚种被认为是该物种的亚种。根据栖息地隔离，这是在中图伦纪末期指定的。新发现的物种仅产于一些较浅的相中。再一次，这两个物种在整个过程中表现出形态上的动态平衡，地理物种形成是瞬间发生的。

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.