How did bivalves diversify during the Ordovician Period?

During the Ordovician Period, bivalves underwent significant diversification, with most modern subclasses represented by definable ancestors by this time. This period was part of a broader, intense interval of marine diversification known as the Ordovician radiation, which saw an increase in the complexity of biological communities and the exploitation of new ecological niches.123

Key aspects of their diversification include:

• Emergence of Subclasses: Several major groups arose during this period, including the Palaeotaxodonta, the extinct Actinodontia, the Pteriomorphia, the Orthonotia, and the Anomalodesmata.1
• Ecological Expansion: While bivalve communities initially occupied various substrates, they increasingly adapted to different habitats through modifications in form. By the Late Ordovician, bivalve communities appeared in shallow-water habitats, eventually displacing existing brachiopod-gastropod communities further offshore.143
• Evolutionary Adaptations: The period saw the development of specialized life habits, such as deep-deposit feeding and deep-burrowing, supported by structural changes like the evolution of gills and siphons.143

This diversification was fueled by the inherent plasticity of the bivalve shell, allowing them to successfully adapt to diverse marine environments.1