Temporal pattern of drilling predation on Cenozoic bivalves-For verifying "Escalation"-

本研究探讨了腹足类作为原生动物的钻孔捕食的时间变化，这足以验证北方太平洋地区新生代期间的“排泄”。因此，得出了以下六个结论。（1）早更新世本州的Glycymeris yessoensis、G.nipponica和Tridonta borealis种群的钻探强度高于北海道的种群。这一结果与达德利和Vermeij（1978年）、Allmon等人（1990年）以及亚历山大和Dietl（2001年）声称的钻探强度向赤道方向增加的说法一致。(2)No在晚新生代，原生动物对虾夷扇贝的钻凿强度存在时间趋势，而上新世的北方扁螺钻凿强度低于更新世。（3）钻孔位置的变化取决于捕食者和被捕食者的种类（虾夷扇贝（G.yessoensis）、北方赤眼蜂（T.borealis）和太平洋海萤（Calyptogena pacifica））。（4）Yessoensis和T.borealis的边缘钻孔最早出现在早更新世种群中，与Vermeij和Roopnarines（2001）一致。（5）虾夷扇贝和北方赤眼蜂的捕食-被捕食体型相关系数在上新世最高，中更新世最低。这似乎与“升级”相矛盾。然而，这种变化可能反映了当地的环境差异。（6）从始新世到中新世，对深水化能双壳类（囊壳类和囊壳类）的钻探捕食作用一直存在。在北海道中新世Morai组的情况下，高强度一样，浅水种被确认在C.太平洋。

This study examines the temporal variation of drilling predation by gastropods as naticids which is adequate for verifying "Esclation" during the Cenozic in the northern Pacific region. Consequently, the following six conclusions have been obtained. (1)The early Pleistocene Honshu populations of Glycymeris yessoensis, G.nipponica and Tridonta borealis show higher drilling intensities than those in Hokkaido. This result is concordant with the equator-ward increase of drilling intensity claimed by Dudley and Vermeij (1978), Allmon et al. (1990) and Alexander and Dietl (2001). (2)No temporal trend in the intensity of drilling on G.yessoensis by naticids during the late Cenozoic is recognized while the Pliocene population of T.borealis show lower intensities than the Pleistocene populations. (3)Drilling-site shifts are depend on the species of predator and prey (G.yessoensis, T.borealis and Calyptogena pacifica). (4)Edge drilling of G.yessoensis and T.borealis first appeared in the early Pleistocene populations, consistent with Vermeij and Roopnarines (2001). (5)Correlation coefficients of predator-prey size in G.yessoensis and T.borealis are highest in the Pliocene and lowest in the middle Pleistocene. This seems to be contradictory to "Escalation". However, such change possibly reflects he local environmental differences. (6)Drilling predation on the deep-water chemosynthetic bivalves as vesicomyids and thyasirids has been observed from the Eocene to the Miocene. In the case of the Miocene Morai Formation in Hokkaido, high intensity like as shallow-water species was recognized in C.pacifica.