No abstract

This paper describes a rich bivalve fauna from the Tubiphytes-Limestone Member (Bithynian, early middle Anisian) of the Caerace Formation in North Dobrogea (Romania). We report 51 bivalve species, including 7 new species and 2 new genera: Atrina multicostata sp. nov., Pinna simionescui sp. nov., Chlamys (Praechlamys) prima sp. nov., Entolium reticulatum sp. nov., Scythentolium anisicum sp. nov., Romaniamya mahmudiaensis gen. et sp. nov. and Praedicerocardium vetulus gen. et sp. nov. The latter taxon represents the oldest Triassic megalodontoid. We provide detailed descriptions of the bivalve fauna, discuss the ecology and compare species richness in the Early and Middle Triassic, showing that the bivalve assemblage of North Dobrogea is much more diverse than all previously described Early Triassic bivalve faunas, but not as rich as several faunas from the late Anisian and Ladinian. The relative richness of the Dobrogea fauna with respect to geologically older and younger faunas suggests that it represents an early stage of the main rediversification of bivalves after the end-Permian mass extinction.

The Schlern and Seiser Alm area (South Tyrol, Italy) is a classical locality for studies of Middle Triassic platform to basin transitions, yet details of the palaeoecology of the rich benthic faunas of this area have been insufficiently known. We present herein a detailed palaeoecological study of the fauna from the Schlernplateau beds (Late Ladinian to Early Carnian) and the more or less time-equivalent Pachycardientuffe (Late Ladinian), which is based on quantitative faunal data. Both the palaeoecology and sedimentary features suggest that the fauna of the Schlernplateau beds represents a lagoonal softbottom fauna. The high species richness of the fauna and the locally restricted occurrences of fossils indicate an open-lagoon setting palaeogeographically close to an ocean inlet. The high evenness of the fauna is probably a result of time-averaging. In contrast, the fauna of the Pachycardientuffe shows clear indications of transportation. Ecological features of this fauna andpalaeogeographic reconstructions suggest three potential source areas: (1) the lagoon represented by the Schlernplateau beds, (2) the reef fringing this lagoon and (3) a shallow clastic coast of a nearby volcanic island and/or submarine high.A comparison between diversities of selected Early and Middle Triassic lithological units revealed the increasing species richness of all major benthic taxa during the Middle Triassic and a shift from bivalve-dominated Early Triassic faunas to gastropod-dominated faunas.