Seed size, fruit size, and dispersal systems in angiosperms from the earlycretaceous to the late tertiary

Fossil data from 25 angiosperm floras from the Early Cretaceous (similar to 124 million years ago) to the Pliocene (similar to 2 million years ago) we re compiled to estimate sizes of seeds and fruits and the relative proporti on of two different seed-dispersal systems by animals and by wind. The resu lts suggest that, first, seed and fruit sizes were generally small during m ost of the Cretaceous, in agreement with previous suggestions, but the tren d of increasing sizes started before the Cretaceous-Tertiary boundary; seco nd, there was a decrease in both seed and Fruit sizes during late Eocene an d Oligocene, reaching a level that has continued to the Late Tertiary; thir d, the fraction of animal dispersal was, in contrast to previous suggestion s, rather high also during the Cretaceous but increased drastically in the Early Tertiary and declined congruently with the declining seed and fruit s izes from the late Eocene; and fourth, the fraction of wind dispersal showe d a bimodal pattern, being high in the Late Cretaceous and in the Oligocene -Miocene but with a drop in between. We find that the observed trends are o nly weakly related to the availability of animal fruit dispersers. Instead, the trends are congruent with a climate-driven change in environmental con ditions for recruitment, where larger seeds are favored by closed forest ve getation. The prevalence of semiopen, dry, and probably herbivore-disturbed vegetation during the Cretaceous, the development of closed multistratal f orests in the Eocene, and the later development of a more open vegetation a nd grasslands starting in the Oligocene-Miocene, are reflected in the distr ibution of angiosperm seed and fruit sizes and in the dispersal systems.