The Mid-Early Cretaceous as a turning point in the evolution of late Mesozoic rhynchonellids of the superfamily Rhynchonelloidea d’Orbigny, 1847

The study of rich rhynchonellid assemblage, collected by layers in the Early Cretaceous deposits of Dagestan, revealed sharp morphological changes of the assemblages at the Barremian-Aptian boundary; the shell exterior and almost all endoskeletal structures changed. The study of morphogenesis of the Late Mesozoic rhynchonellids revealed that boundary in the development of main shell structures during Middle Jurassic-Maastrichtian interval is also in the middle of Early Cretaceous.