Mesozoic marine revolution

The term "Mesozoic marine revolution'' (MMR) (Vermeij 1977) refers to the idea that during the Mesozoic a profound reorganization in the marine communities led to a significant increase in predation pressure and prey species developed various adaptations (thicker shells, spines, behavioral responses) to cope with this increasing pressure ("arms race'' or "escalation''; Vermeij 1987; Harper 2003, 2006). It is undisputed that during the Mesozoic, especially during the Jurassic and Cretaceous, the number of marine grazers as well as durophagous and drilling predators increased considerably (Vermeij 1977, 1987).

This rise in predatory groups was accompanied by profound changes in marine benthic communities. The epifaunal guilds like stalked crinoids and bra-chiopods, which were so characteristic of Paleozoic communities, vanished from shallow-shelf environments, and those epifaunal species that did persist in shallow water do show a high frequency of regeneration and, therefore, predator attacks (Vermeij 1987). A marked shift toward infaunal life modes is documented in post-Paleozoic echinoids, gastropods, and especially bivalves (Stanley 1977; Thayer 1983; Vermeij 1987), although this shift predates the appearance of most shell crushers (Harper 2003). The most conspicuous changes during the MMR occurred in shell architecture. Overall, the shells became sturdier, more highly armored, and developed spines, ribs, and thickened and narrowed apertures (Vermeij 1977,1987; Ward 1981, 1983). At least among gastropods, shell-repair scars became much more frequent, pointing again to increasing predation pressure.

According to Vermeij (1987), it was the biological interactions (competition, predator-prey relations) that led to the evolution of these long-term trends. Yet the biological evolution toward increasing predator-resistant shells might also have been facilitated by changes in the abiotic conditions. Extensive volcanism, which in turn augmented water temperature, high nutrient levels, and a high sea-level stand all facilitated the production of energetically expensive massive shells (Vermeij 1995) and perhaps as well the general increase in diversity and increasing "fleshyness'' of the fauna throughout the Meso- and Cenozoic (Bambach 1993). Secular changes in oceanographic and geochemical conditions most certainly spurred other important changes in the marine biota during middle and late Mesozoic times. Planktonic foraminifers appeared in the Middle Jurassic and became numerically important during the Cretaceous. Coccoliths are known since the Triassic, but they became widespread and abundant during the Late Jurassic and the Cretaceous. This rise in planktonic calcifiers was perhaps facilitated by the intensified bioturbation of the seafloor which effectively recycled nutrients (Kelley and Hansen 2001) but had in turn tremendous effects on the carbon cycle and the CaCO3 saturation of the oceans (Ridgwell 2005).

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