Herring gulls feeding on a recent invader in the Wadden Sea, Ensis directus
The American razor clam Ensis directus has been a successful non-indigenous invader in the Wadden Sea since the late 1970s. It often shows poorly understood mass mortalities in the winter half-year, which are also known from its native area. During such mass mortalities Ensis directus partly leaves its burrow and, as it is unable to re-burrow, is an easy prey for herring gulls during low tide. During a mass mortality in March 1999, Ensis consumption by herring gulls was studied. Shell fragmentation was achieved by shaking the shell vigorously, not by hammering. This caused characteristic shell fragmentation ranging from small fragments broken from one or both valves near the middle, to both valves broken near the middle, but still connected by the ligament. About one-quarter of the shells remained undamaged. No other predators are known to produce similar Ensis shell fragments. In taphonomic studies the importance of predators in fragmenting shells should be taken into account.
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The Evolutionary Biology of the Bivalvia
Bivalves are key components of Recent marine and freshwater ecosystems and have been so for most of the Phanerozoic. Their rich and long fossil record, combined with their abundance and diversity in modern seas, has made bivalves the ideal subject of palaeobiological and evolutionary studies. Despite this, however, topics such as the early evolution of the class, relationships between various taxa and the life habits of some key extinct forms have remained remarkably unclear.
In the last few years there has been enormous expansion in the range of techniques available to both palaeontologists and zoologists and key discoveries of new faunas which shed new light on the evolutionary biology of this important class.
This volume integrates palaeontological and zoological approaches and sheds new light on the course of bivalve evolution. This series of 32 original papers tackles key issues including: up to date molecular phylogenies of major groups; new hard and soft tissue morphological cladistic analyses; reassessments of the early Palaeozoic radiation; important new observations on form and functional morphology; analyses of biogeography and biodiversity; novel (palaeo)ecological studies