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

本研究考察了北太平洋地区新生代腹足类作为水生动物的钻食的时间变化，这足以验证“升级”。因此，得到了以下六个结论。(1)本州早更新世Glycymeris yessoensis、g.b nipponica和Tridonta borealis居群的钻孔强度高于北海道。这一结果与Dudley and Vermeij（1978）、Allmon et al.（1990）和Alexander and Dietl（2001）提出的钻井强度向赤道方向增加的观点一致。(2)晚新生代naticids对g.b yessoensis的钻孔强度没有时间变化趋势，而上新世种群的钻孔强度低于更新世种群。(3)钻探地点的变化取决于捕食者和猎物的种类（g.b yessoensis、t.b orrealis和Calyptogena pacifica）。(4) g.b yessoensis和t.b orrealis的刃钻最早出现在早更新世种群中，与Vermeij和Roopnarines（2001）一致。(5)在上新世，叶氏斑胸草与北方斑胸草的捕食-被食性大小相关系数最高，在中更新世最小。这似乎与“升级”相矛盾。然而，这种变化可能反映了当地环境的差异。(6)始新世至中新世，深海化学合成双壳类动物如囊壳类和囊壳类被发现有钻孔捕食现象。在北海道中新世Morai组中，在c.p oifica中发现了高强度的浅水物种。

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.