Flying high: on the airborne dispersal of aquatic organisms as illustratedby the distribution histories of the gastropod genera Tryonia and Planorbarius

The actual and fossil distribution patterns of the aquatic gastropod genera Tryonia and Planorbarius indicate that avian dispersal was an important di spersal mechanism in the geological past. Combining the distribution histor ies of these genera with ecological data on modern relatives provides insig hts into the process of dispersal of aquatic taxa in general. Avian dispers al of aquatic taxa is facilitated by a variety of factors, including mass o ccurrence in resting/foraging places of migrating birds, ways to attach to the birds and to overcome desiccation during flight, as well as easy reprod uction from a single specimen when introduced into a new habitat. The uncer tain taxonomical status of aquatic organisms, as well as biased preservatio n and sampling, provide serious drawbacks for understanding the importance of aerial dispersal.