ARE PALEOZOIC WIND-POLLINATED GYMNOSPERMS LESS DIVERSE AND LONGER RANGING THAN INSECT-POLLINATED GROUPS?

The pollination syndrome of most Paleozoic gymnosperms is conjectural; however, a good case can be made for wind pollination of cordaites and Callistophyton and for animal (probably arthropod) pollination of medullosans. The saccate morphology and widespread distribution of cordaite prepollen (Florinites, Sullisaccites and Felixpollenites) and Callistophyton pollen (Vesicaspora) suggests that these groups were wind pollinated. All modern conifers (the sister group of the cordaites) are wind pollinated and the size of cordaite prepollen and Callistophyton pollen (35-150µm) is similar to the size of modern bisaccate conifer pollen (15-110µm). Although less is known about the pollination syndrome of the medullosans, the large size (100-600µm) and general scarcity of medullosan prepollen in Paleozoic sediments suggests that this group may have been animal pollinated. Pollination syndrome may be linked to species diversity and stratigraphic range. Wind-pollinated groups are hypothesized to have lower diversity and longer stratigraphic ranges than animal-pollinated groups. A comparison of the species diversity and evolutionary rates of probable wind- and animal-pollinated groups supports this hypothesis. Because the permineralized seeds of cordaites, Callistophyton, and medullosans are readily identifiable at the species level and, within reason, equally susceptible (or resistant) to taphonomic processes, we use seed diversity to test this hypothesis. Our sample consists of seeds in permineralized peat from the Pennsylvanian of Europe and North America. The four genera of putative wind-pollinated seeds (cordaites: Cardiocarpus, Mitrospermum, and Nucellangium, and Callospermarion, the seed of Callistophyton) encompass 9 species (2.25 species/genus), with an average stratigraphic range of 2.3 m.y. The four genera of medullosan seeds (Albertlongia, Pachytesta, Stephanospermum, and Hexapterospermum) encompass 24 species (6 species/genus), with an average stratigraphic range of 1.4 m.y. Mann-Whitney U values indicate that these differences are statistically significantly at the 95% confidence level. Animal pollination may explain the high diversity of medullosans relative to cordaites and Callistophyton.