Baltic Sea as species in 2005 and 2018 respectively, having formerly been confused with more widespread relatives. The tiny Copenhagen cockle ("Parvicardium hauniense"), a rare mussel, is sometimes considered endemic, but has now been recorded in the Mediterranean. However, some consider non-Baltic records to be misidentifications of juvenile lagoon cockles ("Cerastoderma glaucum"). Several widespread marine species have distinctive subpopulations in the Baltic Sea adapted to the low salinity, such as the Baltic Sea forms of the Atlantic herring and lumpsucker, which are smaller than the widespread forms in the North Atlantic. A peculiar feature of the fauna is that it contains a
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