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Fossil Mammals and Early Eocene North Atlantic Land Continuity

Malcolm C. McKenna
Annals of the Missouri Botanical Garden
Vol. 62, No. 2 (1975), pp. 335-353
DOI: 10.2307/2395200
Stable URL: http://www.jstor.org/stable/2395200
Page Count: 19
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Fossil Mammals and Early Eocene North Atlantic Land Continuity
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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."

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