AMMONITE BIODIVERSITY DYNAMICS AND EVOLUTIONARY CONTROLS DURING THE JURASSIC TO LATEST CRETACEOUS

Given their rapid rates of morphological change, expanded paleobiogeographic ranges, and abundant fossil occurrences in Mesozoic marine strata, ammonites have been critical in developing extremely refined biostratigraphic zonations with resolution down to thousands of years in some cases. This biostratigraphic system has served as the foundation for correlation between deposits on every continent. Despite their stratigraphic importance and the robust taxonomic knowledge of this group, relatively little attention has been given to their long-term diversity dynamics (i.e. patterns of diversity and taxonomic turnover rates as measured by extinction and origination) and the possible evolutionary controls underlying them.

Consequently, this study aims to quantitatively establish the long-term genus-level diversity dynamics of ammonites prior to the K/Pg mass extinction event and then assess their possible relationships with abiotic controls during the Jurassic through latest Cretaceous (~130 millions of years). Changes in regional and global ammonite diversity (D), origination rates (OR), and extinction rates (ER) during this time span are compared at different spatial scales (i.e., regional vs. global) to examine the possible role of local and global geographic controls (i.e., open-shelf vs. epeiric sea, latitudinal gradients). Furthermore, to identify possible underlying environmental influences on D, OR, and ER, diversity dynamics will be assessed relative to a suite of various abiotic constraints, including: marine mean global temperature, productivity, as well as marine nutrient recycling and input as measured by sea level and isotopic proxies (i.e., d¹⁸O, d¹³C, d³⁴S, ⁸⁹Sr/⁸⁷Sr, respectively).

Results from this study will provide critical information on ammonite long-term diversity dynamics during an interval that documents a major diversification event in this group. Moreover, considering that ammonites have been one of the most successful (as measured by their abundance and taxonomic diversity) marine groups in Earth history prior to the K/Pg mass extinction event, such information is fundamental to developing a more thorough understanding of the long-term marine evolutionary processes and the biotic impacts of mass extinctions.