This part of our course builds on the assumption that evolutionary change, although being stochastic in principle, is channeled by external and internal constraints to such a degree that it becomes quasi-predictable – or at least understandable. On this basis it makes sense to use the old methods of comparative morphology in the new framework of constructional morphology (Seilacher, 1970) in order to recognize patterns and to interpret them as trends and evolutionary pathways. For such an approach, bivalves are particularly suited:
1. they deviate little from a common design (for instance they never lost their shell).
2. their preservable hard parts adequately reflect the developmental biography of each individual.
3. their shell form expresses the compromise between developmental constraints and functional paradigm with little interference from soft part anatomy, physiology and biotic interactions.
4. they are diversified enough to provide many examples of parallel adaptations for model testing, particularly if we include the fossil record.