Cavidés néocomiens (Bryozoa, Cyclostomata)

Abstract

Four Neocomian species ( Dendroecia neocomiensis, Diplocava biformis, Semicava (?) grandipora and S. (?) multifida sp. nov.) have similarities with the family Cavidae. However, at present, their membership in this family remains uncertain and they are referred to informally as “cavids”. Numerous finds of Bryozoa in the currently accessible localities of the Jura, allow a better description of the two most frequent species. By contrast, Semicava (?) grandipora and S. (?) multifida sp. nov. are rare. New information on these species is derived from material, previously unstudied, found in Campiche collection (Geological Museum of Lausanne) and coming from the old locality of Ste Croix-Chalet du marais. The stratigraphical distribution of Neocomian cavids shows well the crisis affecting the bryozoan fauna of the Jura at the beginning of Trinodosum Zone in the Upper Valanginian. Indeed, of the four species previously present, only one ( Dendroecia neocomiensis) persists and becomes very abundant. It is only in the Lower Hauterivian that Diplocava biformis reappears, and at the same time D. neocomiensis desappears. The hypothesis of cooling of the sea in the Jura during the trinodosum Zone (Walter 1989b) suggests that D. neocomiensis preferred shallow (infralittoral zone) and temperate or cool water, while the other species were thermophilic.