A Faunal History of the North Atlantic Ocean

Abstract

Briggs, John C. (Dept. Zoology, Univ. S. Fla., Tampa 33620) 1970. A faunal history of the North Atlantic Ocean, Syst. Zool., 19:19-34 [Paleoclimate; marine faunas; zoogeography; North Atlantic Ocean].-Our modem, Northern Hemisphere boreal faunas apparently had a dual origin. In Paleocene-Eocene times, one cold-temperate evolutionary center probably became established in the Arctic Basin. Then, as the climate grew colder, another center south of the Bering Land Bridge began its development. During the Oligocene, boreal species were able to move out of the Arctic Basin into the North Atlantic and, in the Pacific, southward from the Bering Sea. By the late Miocene, when a seaway first became established through the Bering Strait, the movement of species was predominantly northward into the Arctic Ocean and thence to the North Atlantic. The second opening of the seaway in the late Pliocene had an even more striking result, transforming the character of the North Atlantic fauna yet scarcely affecting that of the North Pacific. In the contemporary North Atlantic, such characteristic features as a depauperate shore fauna; species with broad latitudinal ranges; the complete lack of an endemic, boreal pelagic group; and the very low rate of endemism at the oceanic islands; present a decided contrast to conditions in the North Pacific. These facts together with good evidence of Pleistocene faunal replacements, latitudinal shifts, and extinctions reveal that the North Atlantic has provided for its marine fauna a more rigorous environment than the North Pacific. It seems clear that alteration in temperature, the one evident variable, was the primary cause. It is concluded that the geographic setting of the North Atlantic with its open exposure to the Arctic Ocean and its relatively small size are the main factors responsible for its history of varied surface temperature. The most severe drops in temperature probably took place during the ice ages of the Pleistocene and these appear to have averaged about 30C below the present winter minimum. The shelf and pelagic surface fauna that becomes established under such conditions is vastly different, in terms of diversity and local geographic distribution, from a fauna occupying a more stable environment.