Late Triassic and early Jurassic dikes and fissures in the Dachstein Limestone in the Northern Calcareous Alpsharbor mass occurrences of the rhynchonellide brachiopods Sulcirostra juvavica and Halorella amphitoma. To testrecent hypotheses about their paleoecology, we characterized these habitats using petrography, carbon stableisotopes, and trace element patterns, and found no evidence for hydrocarbon seepage or hydrothermal venting.Thus the brachiopods lived under normal-marine conditions, in darkness and absence of local photosyntheticprimary production, hence relying on the supply of limited and presumably small-sized food washed into thedikes and fissures. Because Halorella and Sulcirostra occur in dikes and fissures since the beginning of theirstratigraphic ranges, these rhynchonellides are not relics of formerly widely distributed taxa, but instead are twogenera that rapidly adapted to these habitats. Both Halorella and Sulcirostra occur also in late Triassic and earlyJurassic deep-water settings such as deep-marine sills and hydrocarbon seeps, indicating that close phylogeneticrelationships between submarine cave faunas and deep-sea faunas, as seen today, existed also in the earlyMesozoic, albeit among very different taxa. Another analogy to the modern cave fauna is the wide but disjunctgeographic distribution of Sulcirostra and Halorella, both found throughout the Tethys and Panthalassa oceans.Our findings support the view that submarine cave habitats were continuously colonized by new taxa throughoutEarth’s history.