Symposium 3 - Bridging Temporal Scales In Malacology: Uniting The Living And The Dead

Jerry Vermeij (California, Davis) in his keynote address showed the importance of considering context and history as well as morphology and molecular biology. For example, the labial tooth, which occurs in several groups and which may speed up predation, has different possible phylogenies - either gained and then lost or gained independently. Molecular and morphological data cannot resolve the problem, but fossil evidence shows it was achieved by independent gains.

Liz Harper (Cambridge) used modern bivalves to interpret the life habits and morphology of extinct taxa, and experimental modifications of the environment of modern bivalves to test evolutionary hypotheses. Helena Fortunato and Jeremy Jackson (Smithsonian Tropical Research Institute, Panama) assessed the impact of dispersal capability on rates of speciation and extinction by comparing modes of development in the Caribbean and the eastern Pacific. Planktotrophy currently predominates in the more seasonal and more productive Pacific, and protoconch morphology shows that it was also the predominant mode in the Caribbean in the Miocene. Thus the trend towards direct development in Atlantic species may reflect environmental changes rather than a supposedly inevitable evolutionary trend. Klaus Bandel (Hamburg) showed that differences in ornamentation and direction and tightness of coiling of the embryonic and larval shell allow lineages to be followed in fossils. Kaustuv Ray (California, San Diego) concluded that stromboid trends in body size and shape result more from differential extinctions than from evolutionary radiations, so that the pattern of evolution cannot be inferred from living members. Roberto Cipriani (Chicago) looked at drag: drag slows settling of echinoderm larvae and increases their efficiency at passing water through their bodies, and in gastropod larvae it is increased by larval shell architecture so that optimisation of drag produces small planispiral or large trochispiral larval shells. Peter Wagner (Field Museum, Chicago) suggested that rates of change of soft parts of gastropods were significantly greater in the early Palaeozoic than afterwards. Doug Jones (Florida Museum) reported that growth lines in sections of the left valve of the Jurassic oyster Gryphaea show that the well-documented trend to increasing size and reduced curvature was accomplished by accelerated growth rates of later forms rather than than growing for longer before maturity. Antonio Checa (Granada) found the form of the operculum has systematic significance - flexible and multispiral opercula predominate in the archaeogastropods, while rigid spiral opercula dominate among caenogastropods; neogastropod opercula are concentric and rigid. Satoshi Chiba's (Shizuoka) mtDNA study of the phylogeny of Mandarina on a group of Pacific islands showed that species with similar morphologies and life habits appeared repeatedly and independently in different lineages and islands. Pleistocene fossils revealed rapid synchronous shifts in life habits of many lineages. Hybridization occurs in several species, and promotes diversification among populations.