Adaptive strategy of the Late Cretaceous ammonites inhabited offshite waters.

本文报道了采自奥比拉、奥尤巴里和其他一些有详细地层记录的地区的塞内阶和土伦阶的Desmocerar属和Tragodesmoceroides属（软体动物门，海葵总科）的大量标本，首先作了横切面和切向剖面，并对所有种群标本进行了控制形态的一些主要特征的相对生长分析。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特征集的时间变化。由于各性状的地理变异不大，且这些资料都是在地理分布的主要地区获得的，因此这些年代变化被认为是形态演化的基本模式，这些分析结果表明，土鲁阶Tragodesmoceroides subcostatus是从Cenomanian Desmovers japonicum演化而来的，只是表面走向发生了变化。这一物种的形成是在地质学上的瞬时时间在cemomanian和Turoniam之间的边界进行的。D. japonicum是一个在整个物种存续期内保持稳定的物种，而tragodesmoceroides subcostatus被认为是该时代的一个种。I.在生境隔离方面，以中土鲁世末为特征。新物种仅产于较浅的相。这两个种属的Tragodesmocetoides再次显示了持续时间的运动稳态，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.