Quantification of ontogenetic change in Triassic ammonoids

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Mesozoic ammonoids are, with their complex suture lines and rich inventory of shell ornaments, strikingly different from the Palaeozoic predecessors. With the proposed project, the unfolding of conch characters during ontogeny will be introduced as an additional dimension complementing studies of taxonomic diversity and morphological disparity in Triassic ammonoids. The project focuses on two aspects of ammonoid conch growth: (1) The morphological disparity of selected Tethyan and eastern Pacific assemblages of Triassic ammonoids will be analysed and compared with representative Palaeozoic faunas by using quantitative methods such as Fourier Analysis and Principal Component Analysis. We will test if the ammonoids, after their dramatic decline near the Permian-Triassic Boundary, reached similar grades of morphological variation as the species-rich Palaeozoic assemblages. These investigations will focus on the morphometric characters of the conchs. (2) The ontogenetic change of Triassic ammonoid conchs will be quantified with the aim to correlate ontogenetic processes with phylogenetic hypotheses. A method for measuring ontogenetic change in conch morphology will be developed as a tool for Evo Devo studies in ammonoids.