EXTINCTION AND PALEOECOLOGY OF GASTROPODS IN THE MARGINAL SEA

在日本海边缘上新世和更新世晚期的腹足类中，有19种（68%）和10种（77%）已灭绝的腹足类具有非亲营养型幼虫。现存种和灭绝种的幼虫生态学差异不大。因此，幼虫生态学并不是灭绝的原因。日本海边缘地区上新世-更新世以来记录了许多易受古环境变化影响的布氏虫和鼠科动物。它们根据生活深度被细分为两个分类组。钩鳞鱼亚科（Ancistrolepidinae）、海螺属（Neptunea）、白唇鱼属（Buccinum）（L组）主要生活在亚滨带下部的深水中，而珠心鱼属（Nucella）、角口鱼属（Ceratostoma）、八棱鱼属（Ocinebrellus）和石嘴鱼属（Lirabuccittum）（U组）的大多数种生活在亚滨带上部的岩底中。在L组中，日本海一侧的20种和种群（56%）遭受灭绝。有两个物种的化石和活体标本仅在日本海出现。另一方面，U组（10种）中有7种同时生活在日本海和太平洋。在中、晚更新世冰期的低潮期，半封闭的日本海形成了低盐度的表层水和缺氧的深水。因此，L组的许多物种和种群以及U组的少数物种在这种缺氧的深水和微咸的地表水条件下灭绝。在该年龄，必须有中间纯海洋层，使两个特有种的L组生存。大多数能够生活在亚沿岸上层深处的物种并没有灭绝，因为这些物种有可能通过北方浅海峡再次入侵。由此可见，在边缘海中，各物种的深度比幼体生态对物种灭绝的影响更大。

Nineteen living species (68%) and ten extinct species (77%) have nonplanktotrophic larva among the gastropods from the Pliocene and the lower Pleistocene in the Japan Sea borderland. There is not so much differences of larval ecology between the living and extinct species. Thus, the larval ecology dose not act as a causal factor of extinction.Many buccinids and muricids which are vulnerable for the paleoenvironmental change have been recorded from the Plio-Pleistocene of the Japan Sea borderland. They are subdivided into two taxonomic groups based on the living depth. Ancistrolepidinae, Neptunea, Buccinum (L group) mainly live in the water deeper than lower sublittoral zone while most species of Nucella, Ceratostoma, Ocinebrellus and Lirabuccittum (Ugroup) are upper sublittoral rocky-bottom dwellers. In the L group, twenty species and populations (56%) of the Japan Sea side suffered from extinction. Two species occur as fossil and living specimens only in the Japan Sea. On the other hand, the U group (ten species) includes seven species living both in the Japan Sea and the Pacific Ocean.During the lowstands of the middle and the late Pleistocene ice age, low salinity surface water and anoxic deep-water was formed in the semi-enclosed Japan Sea. Thus, many species and populations of the L group and a few species of the U group suffered from extinction in such anoxic deep-water and brackish surface water conditions. At that age, there must be middle pure marine layer which enables for two endemic species of the L group to survive. Most species which are able to live in the upper sublittoral depth did not became to be extinct because it might be possible for these species to reinvade through a northern shallow strait. From the above discussion, the depth of each species is ecologically more important factor to the extinction in the marginal sea than the larval ecology.