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847 
known present and past ranges of such gymnospermous genera as Araucaria Juss., 
Cephalotaxus Siebold & Zucc., Cryptomcria D. Don, Cumiinghamia R. Br., Ginkgo L., 
Glyptostrobiis Endl., Metasequoia Miki, Sequoia Endl., and Sequoiadendron Buchholz (Florin 
1963) and dicotyledonous genera like Cercidiplnjllum Siebold & Zucc., Eucommia Oliver, 
Euptelea Siebold & Zucc., Gunnera L., Nelumbo Adans., Nypa Steck., Pterocarya Kunth, 
Si/mplocos Jacq., Tetracenlron Oliver, and Trapa L. (Krutzch 1989, Thorne 1972,1989) are 
splendid botanical examples. Obvious zoological examples are furnished by the present 
indigenous distribution of the camels and horses, shown by paleozoologists to have 
evolved in North America before becoming extinct there in Pleistocene time. 
5. In the study of patterns of biotic distribution there must be thorough 
understanding of the spread potential (vagility or dispersal) of diverse biotic groups. 
Extrapolation from knowledge of a single group can be most misleading. 
An icthyologist working with only primary-division fresh-water fishes might indeed 
think that long-distance dispersal is equally impossible for all organisms if he does 
not acquaint himself with the biology of other plant and animal groups. 1 suspect 
the antagonism displayed by vicariantists toward long-distance dispersal and toward 
oceanic islands stems from their preoccupation with nonvagile animal or plant groups. 
The relatively recent dispersal of the African cattle egret to and within the New 
World has been somewhat disconcerting for the more extreme vicariantists. 
6. Because of continental displacement and changing climates, oceanic currents 
and changing sea-level, or because of their great vagility, biotic groups have ranged 
widely and often very rapidly over the earth's surface, a few species, some genera, 
and many higher categories becoming subcosmopolitan in range. 
Some groups, like pelagic or migrating birds, normally range widely and rapidly. 
Many aquatic plants are widely dispersed about the world to suitable wetland habitats 
by water or shore birds. 1 have mapped or listed elsewhere (Thorne 1972) 
Ceratophyllum demersum L., Montia fonfana L., Najas marina L., Phragmites australis 
(Cav.) Trin., Potarnogeton pcctinatus L., and many other subcosmopolitan aquatics. 
Many weedy species have become subcosmopolitan due to transportation similarly 
by man, his livestock, fodder for his livestock, farm implements, or ballast. Other 
biotic groups disperse hardly at all over long periods and remain narrowly endemic, 
either due to low vagility or to nonavailability of suitable habitats. 
7. The closest living relatives of a phyletically unplaced taxon are more likely than 
not to be found in the same or adjacent areas rather than on distant continents. 
This principle of phytogeographic plausibility has enabled me to place a number of 
anomalous angiosperm taxa and recognize such apparently natural groupings as the 
Bruniales of southern Africa and Madagascar; Stilbaceae of the Cape Region of 
South Africa, Balanopales in the Rosanae; Drosophyllum Link and Triphyophyllum 
Airy Shaw in the Nepenthineae; and Simmondsia chinensis (Link) C. Schneider in the 
Euphorbiales (Thorne 1975, 1977, 1983, 1985, 1989, 1992). 
8. Major disjunctions on or between continents, when part of a repeated pattern, are 
usually due to normal short-distance dispersal with subsequent major disruption in 
range caused by catastrophic events, geologic or climatic. 
Such catastrophic events are now called vicariance events, some vicariantists thinking 
they have discovered an entirely new approach to biogeography. Biogeographers 
have been using such explanations for centuries. It is true, however, that the revolution 
in geomorphological thinking, namely plate tectonics, has added a significant 
dimension to our vicariance explanations (Thorne 1973, 1978). 
