The Anisian (Middle Triassic) ammonoids of Nevada - An integrated approach to understand morphological change

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In the Anisian stage of the early Middle Triassic ammonoid variability is high off the western coast of Panthalassa and the taxonomic and morphological diversity is remarkable. Superb outcrops in NWNevada in the United States provide the best insight into open water faunas of this part of the world. Thus our approach is characterized by an overall design as a primarily high quantity approach. The largest part of the material can be collected from the spacious outcrops in the desert of Nevada, but the data set is planned be completed by collections of one of our co-operation partner in California and by those parts of the National Museum collection in Washington that are suitable for our approach. Our proposal aims to elucidate the complex interplay between morphological disparity in ammonoids, environmental change, predation stress expressed by bite marks as well as indirect morphological change by adaption. We plan to use multivariate statistics (PAST, R) to discriminate between shell morphologies to obtain a comprehensive view of variability. Based on the taxonomic and morphologic diversity change in the sections we expect to unravel the expected morphological change through time and to elucidate evolutionary pathways. The later will be possible also by support of one of our American co-operation partners who is highly qualified in testing evolutionary hypotheses. Our overall research topic is strongly connected to the Mesozoic Marine Revolution (MMR) that started after the Permian/Triassic boundary with a full reorganisation of ecosystems. The intense radiation of ammonoids in the Triassic, constituting a main portion of macroscopic biomass and falls together with a new development of their potential predators. Among marine reptiles Omphalosaurus was possibly specialised in shell crushing according to this peculiar jaw and teeth organization, and are focussed on in the proposals applied for simultaneously by the Bonn and Berlin working-groups. The compound view of our proposal is added by an assessment of the developmental background of morphological change by a fluctuating asymmetry analysis. This is projected to be based on geometric morphometric methods (including landmarks), enabled by three-dimensional models. The latter we intend to generate from the photogrammetry of ammonites.