CENOZOIC HIGH-LATITUDE GASTROPODS OF THE NORTHWESTERN PACIFIC AND EVOLUTION OF THE MODERN-DAY COLD-WATER FAUNAS

Cenozoic high-latitude gastropod assemblages preserved in the sedimentary rocks of western Kamchatka, range in age from the early Paleocene through early Pleistocene provide an insight into the temporal and spatial patterns of evolution of the modern-day cold water benthic gastropods of the North Pacific realm. Gastropod genera that dominate cold-water molluscan assemblages of the North Pacific today were present in this area since the middle Eocene. During that time, they were a minor component of the middle Eocene largely cosmopolitan assemblage. Striking similarities of the Paleocene and Eocene shallow-water molluscan assemblages of Kamchatka and the western Coast of North America points on the existence of the shallow-marine migration route along the southern margin of the Beringia. Environmental instability triggered by the late Paleogene climatic cooling, which peaked during the early Oligocene caused a selective radiation within Fulgorariinae, Buccinidae, Beringiidae, Neptuneinae, and Turridae. This radiation formed the nucleus of the modern-day cold-water molluscan assemblages. Miocene assemblages were heavily influenced by climatic fluctuations, connected with the intensification of the paleo-Kuroshio current and episodic warming of the high latitudes, peaked at 15.5 and 13.4 Ma. Penetration of warm waters in the high latitudes facilitated migration of large number of temperate and subtropical genera. Pliocene assemblages indicate a gradual cooling. Temperate elements in the Pliocene assemblages are only found in the semi-isolated shallow-marine environments and probably represent relict pockets of the Miocene biota. Restricted migration along the margin of Beringia is indicated by reduction of common species between the Kamchatka, Alaska, and western North America