Evolutionary response of bivalves to the end- Permian mass extinction Habilitationsschrift zur Erlangung der Venia Legendi in Paläontologie an der Universität Zürich vorgelegt von Dr. Michael Hautmann Zürich, 2016

Introduction: The most profound caesura in the >500 Ma history of metazoan life occurred at the end of the Permian (ca. 250 Ma BP), when up to 96 % of marine species and possibly a comparable percentage of terrestrial life went extinct (e.g., Raup 1979; Benton et al. 2004). The Mesozoic era that followed this greatest mass extinction event in Earth’s history witnessed taxonomic rediversification and ecological restructuring that ultimately produced the biotic context of our present-day world. The question whether the end-Permian mass extinction had caused or merely accelerated the transformation from the Palaeozoic into the Modern biosphere initiated a debate about the role of contingency in macroevolution (e.g., Gould and Calloway 1980; Sepkoski 1984, 1996; Raup 1992; Gould 2002) and highlighted the importance of extinction-recovery patterns for developing and testing macroevolutionary models in general (e.g., Hart 1996; Erwin 2001; Brayard et al. 2009). The rationale behind this approach is that mass extinctions provide a natural experiment for studying evolutionary responses of differentially depleted taxa or guilds to a sudden excess of ecological opportunities. In this Habilitation, details of the evolutionary response of the molluscan class Bivalvia to the end- Permian mass extinction are studied from this perspective. Marine bivalves have become a model system for macroevolutionary and macroecological analysis in the fossil record (Valentine et al. 2006, p. 6599). Bivalves owe this privileged status to their generally high preservability, their well-understood taxonomy, close correlation between shell morphology and mode of life that enables autecological interpretations of extinct taxa, and their long evolutionary history that dates back to the Early Cambrian. Moreover, bivalves became dominant in most marine level-bottom communities since the Triassic and are generally the most abundant fossils in shallow marine sediments of post-Palaeozoic age. Accordingly, there is a wide range of studies that address various macroevolutionary aspects of bivalve diversification, particularly with respect to their post- Palaeozoic success in benthic marine communities (e.g., Gould and Calloway 1980; Miller and Sepkoski 1988; Valentine et al. 2006; Roy et al. 2009; Liow et al. 2015). However, such analyses have been based nearly invariably on literature compilations, which suffer from taxonomic inconsistencies, poor stratigraphic resolution, and non-consideration of the ecological context. This Habilitation takes an alternative approach in (i) being rooted in firsthand data from own field collections that include data of the palaeoenvironmental context, (ii) considering the ecological context of the taxa, as derived from autecological and synecological analyses, and (iii) using a coherent taxonomic framework, based on own taxonomic revisions and monographic work on newly collected faunas. The first part of this Habilitation (sections 1–2) documents the progress that has been achieved in these fields, whereas the second part is devoted to the reconstruction and interpretation of long-term trends in the post-Permian evolution of bivalves. These include macroecological trends in response to the proliferation of durophagous (shell-breaking) predators (section 3) and diversity trends at the local, regional, and global level, which form the basis for new models of diversification and diversity partitioning (section 4). Section 5 then focuses on the largest mass extinction that occurred within the Mesozoic and thereby establishes a link between extinction selectivity and changes in ocean chemistry due to sudden CO2 rise. Perspectives for future directions in palaeobiological research are discussed in a concluding chapter