Evolutionary significance of fossil larval shell characters: a case study from the Ostreoidea (Bivalvia: Pteriomorphia)
Nikolaus Malchus, 2000. "Evolutionary significance of fossil larval shell characters: a case study from the Ostreoidea (Bivalvia: Pteriomorphia)", The Evolutionary Biology of the Bivalvia, E. M. Harper, J. D. Taylor, J. A. Crame
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Prodissoconchs of Middle Jurassic oysters possess key characters for a new understanding of the hinge evolution within the Ostreoidea. The ancestral larval hinge most likely evolved from a mytilid-like provinculum through accelerated growth in an antero-ventral direction along a flat, helico-spiral trajectory. The posterior denticles moved into the centre of the hinge axis while the central and anterior denticles were reduced in size and eventually disappeared. The remaining, now central, posterior denticles evolved further into a secondary symmetrical hinge. In most oysters, except for example Tiostrea, the larval ligament maintained its relative position between posterior and anterior denticles, even though this is not obvious in the Ostreidae because of the loss of the anterior denticles. Larval and adult ligaments are continuous. The examined specimens provide further evidence for the plesiomorphic state of planktotrophy within the superfamily. Although additional direct evidence is lacking, consideration of all new available data favour the hypothesis that the postero-dorsal notch is uniquely derived by oysters. The ideas on character evolution put forward in this study are consistent with phylogeny hypotheses based on palaeontological–biological data and recent genetical studies.
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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