GUILD-STRUCTURE AND EVOLUTION OF MESOZOIC BENTHIC SHELF COMMUNITIES

On the basis of the relative abundance of species in 334 literature-de rived paleocommunities the evolutionary history of Mesozoic benthic ma rine macroinvertebrate associations is evaluated quantitatively. The d ata base is analyzed within a framework of five broad environmental su bdivisions (salinity-controlled environments, coarse-grained and fine- grained shallow shelf, mid to outer shelf, and oxygen-controlled envir onments), six time units, and 13 guilds. The guild-spectrum tends to b e broadest in habitats controlled by biological factors. Under more ri gorous and variable physical conditions ecospace is utilized less inte nsely than in stable and predictable environments. The quantitatively documented long-term patterns confirm the results of previous studies which applied a more qualitative approach. Both persisting and evolvin g aspects are evident: The permanence of various guild-assemblages and the evolutionary stability of morphotypes in all studied environments are outstanding features. Superimposed on these conservative aspects is a general trend towards increasingly shallow to moderately deep inf aunal suspension-feeding life habits. This infaunalization can be trac ed back to the success of siphonate heterodont bivalves. Their evoluti onary history illustrates the causal relation between major innovation s, polyphyletic radiations, and the rise in relative abundance and bio mass of an ecological group. The net increase of infaunal organisms wa s largely controlled by a rise in Mesozoic predation pressure and the adoption of new strategies.