A compilation of 37 fossiliferous Phanerozoic marine deposits interpreted to represent ancient hydrothermal vent or cold seep habitats reveals that articulate brachiopods, particularly rhynchonellides and terebratulides, were relatively common constituents of these chemosynthetic settings from the Devonian through the Early Cretaceous but were rare in such paleoenvironments from the Late Cretaceous to the present. Late Devonian vent and seep settings were dominated by rhynchonellides (Dzieduszyckia, ?Eoperegrinella) morphologically similar to Cretaceous seep-restricted Peregrinella, all of which are purported to be closely related phylogenetically. Bivalve genera with extant chemosymbiotic descendants first appeared in vent-seep deposits during the Late Jurassic and were prevalent therein after the Early Cretaceous. These bivalves include members of five families (Vesicomyidae, Mytilidae, Solemyidae, Thyasiridae, Lucinidae); lucinids and thyasirids are the dominant groups represented. Ancient hydrothermal vent and cold seep settings may provide clues to delineate better which factors (e.g., biotic interactions, differential recovery following the Permian-Triassic mass extinction) have influenced overall evolutionary patterns of dominance among brachiopods and bivalves through the Phanerozoic.