動物相からみた日本海の起源(II)

概要

論文の詳細を見る
Based on the facts and principles concerning the evolution and distribution of marine animals, mostly fishes, in the Japan Sea and its neighboring waters in the North Pacific, which were discussed in the previous part of the present study, a consideration was made on the history of development of this marginal sea and its fauna during the Quaternary period. 1. During the early phase of the Quaternary period, possibly Pre-Glacial to First Glacial stage, there must have been a shallow and wide freshwater lake in the place of the present-day Japan Sea. In this lake, freshwater fishes of the Amur River system (Acipenseridae, Leuciscinae, Lefua, etc.) as well as of the survival forms from the ancient or paleo-Japan Sea (mostly salmonids), with a minor component of the tropical sea origin (Epinephelinae : the ancestral forms of Stereolepis and Coreoperca), must have been flourishing. In early half of this phase, the paleo-Amur may have poured directly into the lake and a drain river of the lake may have started somewhere on its southern border and flowed southward across the "East China Sea Plain" and, after uniting with the lower part of the paleo-Yantse Kiang, discharged into a lagoon situated in the north of the presentday Miyako Islands, southern Ryukyu. In the latter half of this phase, the area bordering the southern sides of the lake must have been raised, forming a mountain ridge, and the flow pattern of the river system in the surrounding region markedly changed; the lower reaches of the paleo-Amur are now considered to have worked as a drain river of the lake. 2. It is presumed to have been in First Interglacial stage that the lake first received an inundation of sea water and was transformed through a brackish environment eventually into a marine basin. The invasion of sea water must have been made from north, possibly via the lower part of the paleo-Amur or the drain river of the lake. In the course of thalassification, some of the freshwater animals might have been exterminated or taken refuge in less saline or quite freshwater environment in coastal lagoons and upper reaches of rivers, but others succeeded to adapt or re-adapt themselves to the marine environment. The first marine fish invaders and colonizers of this newly-formed seawater environment are supposed to have been the ancestral forms of the families Stichaeidae and Agonidae, both of which, finding the greater part of the habitat unoccupied in the new environment, have adapted themselves to every (bottom) niches, and carried out a prodigious differentiation somewhat resembling the adaptive radiation, producing many important subfamilies such as Opisthocentrinae, Xiphisterinae, Neozoarcinae, etc. and Tilesininae, Brachyopsinae and Agoninae, respectively. 3. The Japan Sea thus originated must have remained in the connected condition with the Pacific possibly throughout First Interglacial to Second Interglacial stages. In Second Interglacial stage, another sea channel is supposed to have been opened somewhere near the present-day Tsugaru Straits. Through these channels, active interchange of marine fauna may have been done between this marginal basin and the Pacific ; of particular significance may be the emigration of a part of the diversely differentiated stichaeid and agonki fishes to the northern North Pacific and further to the west coast of North America, and also the invasion of the ancestral forms of some primitive groups of the Pleuronectinae (Cleisthenes, Hippoglossoides and Acanthopsetta) and of the Cottidae, particularly the Pseudoblenninae and its related groups (Atopocottus, Alcichthys, Ricuzenius, etc.), from the tropical waters in southeastern Asia and the west coast of North America, respectively. 4. In Third Glacial stage, the Japan Sea was possibly isolated , and within this isolated basin most of the animals may have been differentiated into the species or genera endemic to the marginal sea. During this period, it is further considered, the basin might have been rapidly deepened with a dry climate prevailing, due to which any marked dilution of the sea did not take place and in all probability the Japan Sea has remained as a marine-type basin. Many animal groups may have been transformed into cold-water or deep-water populations under such a environmental condition 5. It is supposed to have been during Third Interglacial stage that the Japan Sea was invaded by more or less specialized, cold-water fishes of such phylogenetically young families as Zoarcidae, Cottidae, Cyclopteridae, etc. from the Okhotsk Sea through the Soya or La Peruse Straits, and by warm-water migratory fishes belonging to, say, the genera Sardinops and Pneumatophorus, certain moderately specialized flatfishes (the genera Liopsetta and Tanakius) and some primitive forms of the subfamily Sebastinae (the subgenus Hatsumeus) from the Pacific possibly through the Tsugaru Straits. During the succeeding isolation phase of the sea in First Subglacial of the Fourth Glacial stage, these fishes have been so differentiated as to yield many endemic species and subspecies. In the same stage of the glaciation, ancestral forms of specialized subgenus of the Sebastinae may have migrated down southward along the eastern side of Asiatic Continent, but could not penetrate into the sea basin under question on account of the untimely close of the sea channels connecting the basin with the Pacific. 6. In First Subinterglacial of the Fourth Glacial stage, the two channels were possibly reopened, and through these channels a part of the populations of Zoarces viviparus and Sebastes (Hatsumeus) owstoni might have emigrated to the Pacific and further northward into the Bering Sea, and, upon the formation of the Bering Straits, migrated into the North Atlantic probably through the seas of the Canadian Arctic Archipelago. An immigration by the flounders of the genus Limanda may be another important topic at this stage in the history of the Japan Sea fauna. 7. It was probably not until Second Subglacial of the Fourth Glacial stage that the Korean Channel was formed, and it may have been presumably during the following Subinterglacial stage that the Tsugaru Straits was firmly established. The Soya Straits (as well as, possibly, the Tartary Straits), on the other hand, was not yet settled and may have repeated opening and closing for a few times furthermore according to the changing sea level in the succeeding subglacial and subinterglacial phases in Fourth and PostGlacial stages. Such an intermittent isolation may be responsible at least partly for the great variety and variability observed at present on the representatives of many species of zoarcids, cottids, liparids, etc. which had immigrated from the Okhotsk Sea in the preceding Interglacial stage; and a rapid speciation is on progress in these phylogenetically quite young fish groups even at this moment in the "Fourth Interglacial" stage.
地学団体研究会の論文
1964-11-30

動物相からみた日本海の起源(II)

スポンサーリンク

概要

著者

関連論文

スポンサーリンク