Some Aspects of Plant Geography of the Northern Hemisphere During the Late Cretaceous and Tertiary

Palynological data emphasize the presence of two distinctive provinces during the Late Cretaceous, one including eastern North America and Europe and a second including the major part of Asia and western North America.The distinction between these two provinces became increasingly blurred during the Paleogene.During the Eocene, the rain forests of both Europe and western North America shared numerous genera, both extinct and extant.The great majority of the latter and most of the closest extant relatives of the former now occur in the Indomalayan region.It is thus clear that much of the present Indomalayan flora represents a relict of a once widespread Northern Hemisphere tropical (s.l.) flora, one that has largely (but not entirely) been eliminated from the New World.Among the possible New World survivors of this boreotropical flora are some of the dry Caribbean genera, which could have been derived from lineages of the dry tropical vegetation of the Gulf Coast Eocene; only a handful of present Neotropical lowland rain forest genera appear to be boreotropical relicts.Much has been postulated concerning the historical biogeography of the floras of the Northern Hemisphere during the Cretaceous and Tertiary (e.g.Chaney, 1940;Takhtajan, 1969), but many of the suggested migrations and many of the suggested relationships have either turned out to be based on serious misinterpretations of the ages of various fossil floras or on invalid determinations.

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