Abstract

The Mesozoic marine revolution focuses on increased predation by durophagous (shell-crushing) predators and the concomitant evolution of prey organisms that occurred in the Mesozoic. Evidence of this predator/prey revolution is found in the appearance and increase of new types of predators that can crush hard shells of prey organisms, and is also found in the morphological changes of prey organisms, such as the appearance of a protective shell morphology of gastropods. We present new data based on the occurrence of shell fragments that indicate a slower increase in durophagous predation than has been considered previously.

The results of an experiment on shell abrasion, in which shells were tumbled in barrels with sediments, indicate that incomplete bivalves and gastropods with angular margins from shallow-marine deposits can be considered as good evidence of durophagous predation. Such angular shell fragments are virtually absent from Japanese Mesozoic shell beds, whereas they are occasionally or commonly found in the Paleogene and are usually abundant in Neogene shell beds. The dominant occurrence of fossil shell fragments in the Cenozoic, as well as the data from shell abrasion experiments using tumbling barrels, indicates that wave agitation or currents do not produce shell fragments with angular margins. Such angular shell fragments are interpreted as the result of durophagous predation that has increased during Cenozoic time, and can be a useful tool in estimating durophagous predation in the fossil record. Revised data on the number of durophagous predator taxa (crustaceans and teleostean fishes) also support this conclusion.

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