EXTINCTION AND PALEOECOLOGY OF GASTROPODS IN THE MARGINAL SEA

在日本海沿岸的上新世和下更新世腹足类中，有19种（68%）现存物种和10种灭绝物种（77%）具有非浮游营养的幼虫。现存物种和灭绝物种之间的幼虫生态并没有太大的不同。因此，幼虫生态并不是导致灭绝的原因。自上新世-更新世以来，日本海陆缘记录了许多易受古环境变化影响的虫类和杀虫类。根据生活深度，它们被细分为两个分类群。Ancistrolepidinae、Neptunea、Buccinum （L组）主要生活在下海下更深的水域，而Nucella、Ceratostoma、ocinebellus和Lirabuccittum （u组）的大部分物种都生活在上海下岩底。在L组中，日本海一侧有20种和种群（56%）灭绝。只有两种以化石和活标本的形式出现在日本海。另一方面，U组（10种）包括生活在日本海和太平洋的7种。在更新世中期和晚更新世冰期低洼期，在半封闭的日本海形成了低盐度地表水和缺氧深水。因此，在这种缺氧的深水和微咸的地表水条件下，L组的许多种和种群以及U组的少数种灭绝了。在这个年龄，必须有中间的纯海洋层，使L群的两个特有物种能够生存。大多数能够生活在浅海深处的物种并没有灭绝，因为这些物种有可能通过北部的浅海峡重新入侵。综上所述，各物种的深度在生态学上比幼虫生态学对边缘海的灭绝更为重要。

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.