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 southern North Sea Caledonians slowly phase into the Variscan orogeny. The break up of Pangea occurs during the Kimmerian tectonic phase for most of the Mesozoic, until the early-mid Cretaceous, this marks the start of creating the present position of our continents today. During the Jurassic, rifting activity reaches its maximum and North America starts to move apart from Eurasia following that event in the Cretaceous the southern part of North America starts to open up the Atlantic Ocean with the separation of South America and Africa. At the end of the Mesozoic the North Sea reached its final position where it lies