Skeleton of the Fossil SharkIsurus denticulatusfrom the Turonian (Late Cretaceous) of Germany—Ecological Coevolution with Prey of Mackerel Sharks

摘要

AnIsurus denticulatus(Glickman, 1957) shark skeleton from the late Turonian (Late Cretaceous) of Germany is described within a diverse upwelling influenced fish fauna of northern Germany, Europe. It was found in the turbiditic marly limestones at the submarine Northwestphalian Lippe Swell in the southern Proto-North Sea Basin. Compared to modern mackerel sharkIsurus oxyrinchusRafinesque, 1809, including cranial denticles, this allows a revision of the younger synonym “CretoxyrhinaGlickman, 1964”. Within the CretaceousIsurus, a loss of the lateral tooth cusps and nutritive clefts of the roots (considered as plesiomorphic character of the Lamnidae) took place from the Albian (Early Cretaceous) to the Campanian (Late Cretaceous). The tooth morphology changed during the Albian-Turonian from a tearing (I. denticulatus) to a cutting (I. mantelli) type (Coniacian-Campanian). The complete lateral cusplet and symphyseal teeth reduction inIsurusat the end of the Cretaceous seem to be a result of the coevolutionary changing feeding habits of a worldwide expanding shark. In a second evolutionary adaptation, parallel to the new radiation of marine mammals (Paleocene/early Eocene), fromIsurus, the white shark ancestors (Carcharodon) seem to originate. In another radiation fromIsurus, coevolving with appearance of dolphins and further marine mammal evolution within the Middle Miocene, a second timeIsurusdeveloped serrated teeth (I. escheri).