%0 Journal Article
%T Skeleton of the Fossil Shark Isurus denticulatus from the Turonian (Late Cretaceous) of GermanyˇŞEcological Coevolution with Prey of Mackerel Sharks
%A Cajus G. Diedrich
%J Paleontology Journal
%D 2014
%I Hindawi Publishing Corporation
%R 10.1155/2014/934235
%X An Isurus 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 shark Isurus oxyrinchus Rafinesque, 1809, including cranial denticles, this allows a revision of the younger synonym ˇ°Cretoxyrhina Glickman, 1964ˇ±. Within the Cretaceous Isurus, 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 in Isurus at 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), from Isurus, the white shark ancestors (Carcharodon) seem to originate. In another radiation from Isurus, coevolving with appearance of dolphins and further marine mammal evolution within the Middle Miocene, a second time Isurus developed serrated teeth (I. escheri). 1. Introduction Macroneoselachians have in most cases ancestors reaching into the upper early or lower Late Cretaceous (e.g., [1¨C6]). The largest shark of the lower-middle Late Cretaceous (Cenomanian-Campanian) was described as Isurus [7, 8] or Cretoxyrhina [9] controversially until today (e.g., [6]), which was globally distributed (Figure 1(a)). Cretaceous and Tertiary shark researchers did not review the isurid sharks in the past critically, whereas complete skeletons are rare form different stratigraphical units (e.g., [6, 10]). The revision of Mesozoic Isurus and its evolutionary trend, especially in the dental morphology change, is highly important to understand its fairly long evolutionary trend, which is the basic to understand the white shark evolution and non-origin of megatooth sharks from isurid ancestors (cf. [3]). Whereas the dentition changed already strongly in the Cretaceous (e.g., (cf. [11¨C15]), and herein continuing in the Tertiary), it can be demonstrated, that the squamation and vertebrae retained with plesiomorph characters. Those are found similar at modern Isurus (cf. [5]), and Cretaceous
%U http://www.hindawi.com/journals/paleontology/2014/934235/