The Morphologic History of Paleozoic-Triassic Ammonoids

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9706232 Saunders The proposed research will focus on three major themes concerning Paleozoic-Triassic ammonaid cephalopods: 1. Analysis of variation in suture-inclusive, whole-shell morphology and morhphologic diversity through space and time (Devonian-Triassic), using principal components analysis (PCA) of a 21-character set for each taxon; 2. The evolution of ammonoid suture complexity through time, as a single-character measure of biological complexity, and with respect to evolution of suture complexity in different ammonoid clades; and 3. The effects of extinction events on ammonoid morphospace, and on morphologic and taxonomic diversity, focusing on three major crises: the U. Devonian Frasnian/Famennian, the Devonian/Carboniferous, and the Permian/Triassic. The scope is unprecedented in ammonoid investigations, in terms of (a) its time span (~190 my); (b) the comprehensive treatment of all 627 Paleozoic ammonoid genera (212 Devonian, 263 Carboniferous, 152 Permian) plus an additional subset of 25-30 genera (75-100 species) of basal Triassic ammonoids. Additionally, in order to precisely evaluate the timing of major extinction's and to assess susceptibility, persistence, and recurrence of shell morphotypes to these events, we will undertake PC analysis of variation in a combined total of 700-750 species (~150 genera) present during the ca. 0.5-5 my intervals spanning each of the three extinction episodes. This research will be the most complete morphometric treatment of Paleozoic and early Mesozoic cephalopods ever undertaken. It will generate a 21+ character morphometric data-set for more than 600 ammonoid genera and an additional 700+ species that is taxonomically up-to-date, complete and stratigraphically precise. The time-stepped analysis by PCA will permit documentation of how clades evolved, changed in morphologic diversity and richness, and how they responded to biotic crises. The results will have bearing on the interpretation of macro-evolutionary change, the evo lution of complexity, the influence of morphologic constraints and extinction events on variation and diversity, all on a time scale of nearly 200 million years.