Abstract Marine bivalves of the eastern Pacific continental shelf show a strong diversity gradient from the Arctic Ocean to the tropics. This gradient is underlain by strong diversity trends in both infaunal and epifaunal bivalves, contrary to Thorson's influential hypothesis ( 1952 , Verhandlungen der Deutschen Zoologischen Gesellschaft, 1951, 267–327), and is significantly correlated with mean sea-surface temperature; either raw data or a residuals analysis yields p < 0.0001. Patterns differ according to trophic group and phylogeny; however, suspension feeders conform to the general bivalve diversity gradient, as do facultative deposit feeders such as tellinids, while deposit feeding protobranchs do not. Infaunal and epifaunal diversity gradients have different slopes so that their ratio changes with latitude; data on Jurassic and Cretaceous bivalves suggests that this ratio has varied in slope and intercept over geological time.

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