Mediterranean fossil whale falls and the adaptation of mollusks to extreme habitats

The hypothesis that sunken carcasses of Mesozoic marine reptiles and Cenozoic whales acted as evolutionary stepping stones to deep-sea reducing habitats is underlain by the question of whether vent-like, chemosymbiotic specialization first evolved at shelf depths. Fossil skeletons of large whales have long been known from ancient shallow-water strata, but they have never been considered as a source of information on ecosystem development. We present a study on a 3 Ma old fossil whale fall and a survey of other Pliocene fossil skeletons to show that the associated biota is dominated by heterotrophs, with subsidiary chemoautotrophs. The taphonomy of the Mediterranean shelf whale falls shows some differences with respect to deep-water studies. Quantitative analyses of abundance data within a large data set on fossil and modern mollusk families confirm that deep-and shallow-water communities at reducing habitats are composed of a different set of taxa, i.e., specialists occurring only below the shelf break. Mediterranean carcasses sunken in coastal settings do not seem to be favorable for the evolution of whale-fall specialists among the mollusks. The situation reverses as the shelf break is approached.