an update on Lamarck's and Brocchi's faunas

The lower-middle Eocene is characterized by the highest temperatures of the Cenozoic, a greenhouse climate much different from the icehouse temperatures of the last 3 million years. Eocene subtidal mollusk communities from sandy bottoms of the Pyrenees and the Paris basin had a very high diversity and were dominated by the same families of modern seas, with similar abundance distributions. On the other hand, intertidal and very shallow subtidal settings hosted a fauna much more different from the modern. Intertidal settings in Western Europe were dominated by the potamidids, a group of gastropods today thriving in mangrove-fringed coasts, but with a much lower diversity than during the Eocene. At the same time, very shallow subtidal bottoms were characterized by ampullinid gastropods, a family containing only one extant species, an algal grazer. It is suggested that peculiarities of Eocene mollusks were connected to the ongoing diversification and increase in biomass of plants.