Uniform habit spectrum vs. taxonomic discrepancy between two succeeding Triassic coral faunas: A proof of the intra-Norian faunal turnover

Triassic coral fauna from the Tethys Ocean contains, besides colonial cerioid, meandroid and thamnasterioid corals, a high percentage of solitary and pseudocolonial, phaceloid corals with exclusively epithecal walls, about one-fifth of the genera with micromorphology of septa having pennules or menianes. These features are significant indications of moderate depth environments of low energy level and reduced illumination. Despite a uniform spectrum of growth forms, microstructural criteria allow discriminating a middle Anisian-early Norian (A2-N1) fauna from the middle/late Norian-Rhaetian (N2/3-R) one. Taxonomy of the two faunas shows meaningful differences: of four families that dominated in A2-N1 fauna, Volzeiidae, Conophylliidae, and Tropiastraeidae are absent from the N2/3-R fauna and Margarophylliidae are present in a considerably reduced volume. As a consequence of reduction of the earlier corals, particular morphologies were eliminated. In the N2/3-R fauna, five families are abundant: the solitary and phaceloid Reimaniphyllidae and Stylophyllidae, along with colonial Cuifastraeidae, Pamiroseriidae and Astraeomorphidae, all known as rare and rudimentary elements in the earlier fauna. hange in faunal content in the Tethys during the Norian was controlled by environmental factor(s) hardly identifiable by simple observation, as this is not connected with any obvious facies or change in coral growth form.