Fauna of Europe of the Baltic Sea has led to the evolution of many slightly divergent species, such as the Baltic Sea herring, which is a smaller variant of the Atlantic herring. The most frequent benthic species are "Saduria entomon" and "Monoporeia affinis", which is originally a freshwater species. A great part of its bottom is anoxic and without animal life. The Baltic Sea and North Sea are also home to a variety of marine mammals (common seals, grey seals). Europe contains several important freshwater ecoregions, including the heavily developed rivers of Europe, the rivers of Russia, which flow into the Arctic, Baltic,
Geology of the North Sea As the rifting stopped, then regional subsidence occurred creating an intracratonic sedimentary basin. Subsidence occurred due to lithosphere cooling. Some of this uplift was along old lines of weakness from the Caledonian and Variscan Orogenies long before. Intraplate compression was caused when the Atlantic Ocean basin formed. the Mid-Atlantic spreading ridge has been busy separating east from west. Greenland separated from North America and the rifting altered direction during the Paleogene, which caused Northern Europe to separate from Greenland. During the Eocene period, the last land bridge across the Atlantic sank. The Alpine Orogeny that occurred about 50 Ma was