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most cases the animals benefited as well from this coevolutionary association. Wind and water pollination syndromes also allowed for outcrossing and have continued to exist since the Early Cretaceous. However, they have never developed the diversity of those angiosperms pollinated by animals. Also several abiotically pollinated angiosperms, for example the Fagaceae (Quercus or oaks) and the Juglandaceae (Carya or pecans), later accommodated themselves for animal dispersal of their fruits or seeds. The importance of outcrossing cannot be underestimated as a driving force in the evolution of the angiosperms (Dilcher, 1995, 1996).

The ability of the angiosperms to accommodate and maximize benefits from animal behavior has been responsible for the evolutionary success of the group. As individual clades made use of particular coevolutionary strategies the diversity of both the angiosperms and animal groups increased. The benefits to the angiosperms were the benefits of the genetics of outcrossing. Because this is a sexual process, it was accomplished by means of evolutionary changes to flowers and fruits and seeds. This is why these particular organs have been centers of angiosperm evolution and why they are so useful in angiosperm systematics today.

I acknowledge with thanks the help of Terry Lott and Katherine Dilcher in the preparation of this manuscript. Thanks to Peter Raven who read and commented on this paper and also to the many students and J. William Schopf and colleagues who shared perspectives of angiosperm evolution with me. I thank the organizers of the symposium at which this paper was presented: Francisco Ayala, Walter Fitch, and Michael Clegg.


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