PALEOECOLOGY AND EVOLUTION OF MESOZOIC SALINITY-CONTROLLED BENTHIC MACROINVERTEBRATE ASSOCIATIONS

Salinity-controlled benthic macroinvertebrate associations are typical of many Mesozoic marginally marine environments. They can be recogniz ed by abiotic criteria (e.g., environmental setting, specific autigeni c minerals), by biotic criteria (faunal composition, diversity, shell morphology, size-frequency histograms, taphonomic features, associated microfauna and microflora), and by isotope geochemistry of shells. Al though salinity-controlled associations must have been widespread in t he European German Triassic, very little is known about their ecology. They appear to have been dominated by the bivalve Unionites and the b rachiopod Lingula. In the Jurassic, brackish-water associations are ch aracterized by bivalves, in particular neomiodontids, corbulids, mytil ids, bakevelliids, isognomonids, and oysters. In the Cretaceous, in ad dition, corbiculid bivalves and gastropods become increasingly abundan t. Salinity-controlled benthic macroinvertebrate associations can be u sed to reconstruct salinity regimes of ancient environments, but empha sis should be placed on an integrated sedimentological and ecological approach, as salinity is rarely the only parameter influencing faunal composition and diversity. Although the species composition of salinit y-controlled benthic associations changes distinctly through time, the composition of morphotypes remains surprisingly constant throughout t he Mesozoic and up to the Recent, evidence of a conservative evolution of benthic faunas within marginal marine high-stress environments.