Chemosynthesis-based ecosystems around methane seeps often have lots of bivalves. In the past, it was believed that brachiopods dominated these environments before bivalves. However, a recent discovery shows clusters of bivalves in the oldest-known methane seep from the late Silurian period. These bivalves, similar to modern chemosymbiotic ones, belonged to the Modiomorphidae family and lived in seeps with increased fluid flow alongside atrypid brachiopods. This suggests that bivalves colonized seep habitats as early as brachiopods and developed specialized lineages to thrive in these environments. Rich bivalve communities are not just successors to brachiopods but have been a recurring feature in the evolution of chemosynthetic ecosystems.