Fossil Mammals and Early Eocene North Atlantic Land Continuity

Abstract

Until recently American vertebrate paleontologists, particularly students of fossil mammals, have not generally accepted the concept of a former continuous land area around the north end of the Atlantic, connecting western Europe with North America.G. G. Simpson developed biological arguments based on fossil mammals supporting the existence of a corridor (Simpson, 1953 and references cited there) topologically connecting western Europe with North America in the early Eocene, but Simpson was influenced by the stabilistic geologic rationale of the times when he located the position of the corridor in Asia because of supposed permanence of the Atlantic oceanic barrier during all of Tertiary time.He did not take into account the epicontinental Turgai Straits sea barrier in Asia that lay athwart his corridor in the early Tertiary.The plate tectonic geophysical synthesis of the history of the North Atlantic and Arctic Oceans is in accord with the mammalian timing evidence that a former Euramerican landmass as well as a biota was severed about 49 m.y.ago and that Holarctic land dispersal since that time has been via Asia alone, becoming possible again with Europe in the mid-Tertiary.Earlier, starting about 70 m.y.ago, a continental collision whose site is now within northeastern Siberia created land continuity between what were then Asia and North America, and by the Oligocene the Turgai Straits had finally dried, giving the Holarctic corridor essentially its present configuration.Shallow epicontinental waters have on several occasions crossed Beringia, as at present.Thus the land surface of Holarctica has been rearranged substantially since 70 m.y.ago, North America as a land surface having shifted its allegiance from Europe to Asia.Recently published geological and geophysical information also suggests that, in addition to early Eocene land continuity in the Greenland-Barents Shelf area, a subaerial dispersal route crossing the volcanic Wyville Thompson Ridge from southeastern Greenland to the Faeroes and then to Great Britain and Ireland may also have been possible for a time in the early Tertiary.This latter route is the long familiar but hypothetical Thulean Bridge, now given a new lease on life by geophysical studies of "hot spots."Aside from the time-honored and romantic concept of Atlantis, a rationale for a former North Atlantic land area connecting western Europe all the way to the North American mainland can be traced back at least to the 18505.The concept reached a high level of credibility among biogeographers such as Scharff (1907, 1909, 1911) and geologists such as Arldt (1917), and the connection was usually thought of as operating up until rather late in the Cenozoic.It should be recalled that until Nansen's historic voyage in the Fram in 1893-1896 it was generally believed that the Arctic Ocean was shallow and that a significant amount of unknown land still lurked in those waters-land that might somehow have been a terrestrial dispersal route in pre-glacial times.In its extreme form, the idea of a transatlantic late Cenozoic land bridge in the north is still with us (e.g., Strauch, 1970), although the postulated locale is regarded as Iceland rather than farther poleward.On the other hand various authors, for instance Simpson (1953, 1965), Schwarzbach & Pflug (1957), and Schwarzbach (1959), have claimed that no connection between Iceland and the British Isles existed after the Eocene or that none existed at all during the whole Cenozoic Era.Still other authors have sug-