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range emerges as the best predictor of survivorship in marine bivalves, and argue that such indirect effects are probably more important than generally appreciated. I will also discuss regional variations in the balance of invasions and local origination in the aftermath of the K-T event, which are somewhat unexpected given that the extinction itself tended to increase biotic homogenization on a global scale by preferentially removing the more localized taxa. Invasions and extinctions are also important during times of “normal” extinction intensities, as I will illustrate with reference to the dynamics of the latitudinal diversity gradient. I will conclude with some implications for integrating insights for past and present-day extinctions and suggest that a powerful approach might involve comparative dissection in extinction patterns according to likely drivers. Throughout I will note gaps in our understanding that would benefit from combined study of modern and ancient systems.

In this chapter, I will focus mainly on marine bivalves such as mussels, scallops, and cockles. Bivalves are becoming a model system for the analysis of large-scale biogeographic and evolutionary patterns (Crame, 2000, 2002; Jablonski et al., 2003b, 2006; Kidwell, 2005; Valentine et al., 2006; Krug et al., 2007) for several reasons. They are taxonomically rich but not unmanageable (≈3,000 living and fossil genera), and their systematics are increasingly understood, so that taxonomic standardization and phylogenetic treatment of heterogeneous data are feasible. They have diverse life habits, from filter-feeding to photosymbiosis and chemosymbiosis to carnivory. They occur at all depths from the intertidal zone to deep-sea trenches and from the tropics to the poles. They are abundant and often well preserved as fossils [although not all habitats and clades are equally represented; Valentine et al. (2006)], and they have diverse shell mineralogies and microstructures, which allows analyses to control statistically for, and thus factor out, some, although not all, of the biases in the fossil record (Kidwell, 2005; Valentine et al., 2006). These favorable attributes do not mean that the bivalve fossil record is perfect, and preservation and sampling biases must always be considered in large-scale analyses [see, for example, the variety of approaches in Alroy (2000), Foote (2003), Bush and Bambach (2004), Bush et al. (2004), Jablonski et al. (2006), and Smith (2007)]. However, our growing knowledge of living and fossil bivalves, including the taxonomic, preservational, and geographic factors that can distort their fossil record, makes this group an excellent vehicle for integrating present-day and paleontological diversity dynamics.

EXTINCTION SELECTIVITY CHANGES AT THE MOST EXTREME EVENTS

A broad array of organismic and clade-level traits enter into extinction risk for present-day species. For example, in evaluating extinction



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