TIFFNEY, BRUCE H.* AND STEVEN R. MANCHESTER. Department of Geological Sciences, University of California, Santa Barbara, CA 93106 and Paleobotanical Laboratory, Florida Museum of Natural History, Gainesville, FL 32611. - Physical Influences on Phytogeographic Continuity in the Northern Hemisphere Tertiary.
The phylogeographic patterns of Northern Hemisphere angiosperms
reflect the dynamic interplay between plate tectonics, climate and
terrestrial biota during the last 100 Ma. Barriers including oceans,
mountains, deserts, day length, available precipitation, and seasonal
temperature influenced the dispersal, genetic isolation, and
evolutionary diversification of terrestrial plants and their dependent
animals. The major physiographic barriers to early Tertiary land
organisms were oceanic, restricting exchange to higher latitudes
between Eastern Asia and North America (The Bering Land Bridge) and
North America and Europe (The North Atlantic Land Bridge). Europe and
Asia were separated by the Turgai Strait. While boreal climate was
relatively warm, winter day length may have posed an added barrier at
the more northerly latitudes. Global cooling near the end of the
Eocene introduced the further barrier of continental climates hosting
herb-dominated biomes in midcontinental North America and Eurasia,
aided locally by the growth of the Rockies (North America), the
Alpine Orogeny (Europe), and the retreat of the Turgai Strait
(Eurasia). By the Late Tertiary, continued tectonism, including the
rising Himalayan Mountains, increased the intensity of seasonal
changes. The Pleistocene ice ages further restricted intercontinental
exchange to cool-temperate and Arctic forms, while decimating
warm-temperate and subtropical clades in Europe and North America.
The basic geological and paleoclimatological evidence for these
environmental changes is now relatively well known. However, several
finer-scale questions remain unanswered. Does short winter day length
really pose a barrier to evergreen plants in warm northerly latitudes?
Did ephemeral migration routes allow brief pulses of biotic exchange
during climatic transitions, e.g., allowing warm-temperate elements to
move between Europe and Asia in the middle Tertiary? What is the role
of herbs in early Tertiary floras, where they are generally poorly
represented?
Key words: Angiosperm, Phytogeography, Tertiary