During 2010-2015 the authors revisited the massive collection of marine mammal fossils in Naturalis Biodiversity Center, Leiden, The Netherlands. Between the thousands of postcrania collected by a single expedition at the Schelde estuary in 1961 they noted some fragmented but important toothed whale (Odontoceti) cranial specimens. This article reports on fossils of a narwhal (Monodontidae), a large beaked whale (Ziphiidae) and dolphins related to the Amazon river dolphins and the La Plata dolphin (Inioidea), which at times between the middle Miocene and early Pleistocene inhabited the North Sea realm.