560 Paläontologie; Paläozoologie
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The aim of this study was to assess distribution patterns of articulate brachiopods during the Mesozoic. Exploratory and confirmatory multivariate analyses in this study evaluate whether environmental preferences of brachiopods and bivalves are substantially distinct and whether structure of their communities significantly differ. Specifically, the hypothesis being tested is that differential abundances of Mesozoic brachiopods and bivalves are not related to varying substrate properties only, but also to varying food supply, turbidity and oxygen levels. This hypothesis was evaluated with quantitative data gathered in various field areas and time intervals. They include the Upper Triassic deposits of the West Carpathians and Eastern Alps, the Lower and Middle Jurassic deposits of Morocco, the Middle and Upper Jurassic deposits of the West Carpathians, the Upper Jurassic deposits of the Franconian and Swabian Alb, and the Upper Jurassic deposits of the Swiss Jura. The main conclusion is that brachiopod-dominated communities are characterized by a unique guild structure, with dominance of trophic groups with low metabolic requirements or adapted to nutrient-poor or oxygen-poor conditions. For example, brachiopod co-occured more commonly with epifaunal than with infaunal bivalves in soft-bottom environments. Abundances of brachiopods correlate mostly negatively with increasing proportions of terrigenous admixture (i.e., with increasing amount of land-derived nutrient supply and turbidity).
The Upper Cretaceous Ajlun Group (Cenomanian-Turonian) of southern/south-eastern Jordan has been analysed in 15 detailed sections with thicknesses between 40 m and 200 m. Taxonomic, palaeoecological, taphonomic, and sedimentological aspects were taken into account. During the early Upper Cretaceous the study area was situated at the south-eastern margin of the Tethys Ocean, between the palaeo-shoreline in the south-east and an offshore carbonate platform in the west. Thus, the measured sections include a complete facies succession from terrestrial-dominated environments via marginal marine siliciclastics to an area of carbonate precipitation. So far, very little is known about the fauna and the depositional environment of the group, especially of the transitional marginal marine part. Also, in depth studies of the Cretaceous fauna of southern Jordan are very rare. Therefore, the benthic fauna of the area is described in an extensive taxonomic chapter. It consists of 117 taxa, 77 of which are bivalves, 22 gastropods, 9 echinoids, and 4 corals. The phyla Porifera, Bryozoa, and Brachiopoda are represented by 1 species each. Additionally, at least two species of decapod crustaceans were found. One bivalve species is new: Anthonya jordanica from Cenomanian claystones of the eastern study area. 41 quantitative samples of the benthic invertebrate fauna were grouped into nine associations and three assemblages by means of a Q-mode cluster analysis. These are described as remnants of former communities and their environments are discussed. Salinity and substrate consistency are assumed to have been the most important environmental parameters controlling the faunal distribution. The overall palaeo-environment is discussed on the basis of sedimentological and palaeoecological results. It was primarily influenced by the morphology of the sea floor, sediment supply, and salinity of the sea water.