Table of Contents
Paleontology Journal
Volume 2014 (2014), Article ID 934235, 20 pages
http://dx.doi.org/10.1155/2014/934235
Research Article

Skeleton of the Fossil Shark Isurus denticulatus from the Turonian (Late Cretaceous) of Germany—Ecological Coevolution with Prey of Mackerel Sharks

Private Research Institute Paleologic, Petra Bezruce 96, CZ-26751 Zdice, Czech Republic

Received 19 May 2013; Accepted 24 July 2013; Published 13 May 2014

Academic Editors: A. Garcia-Alix, A. M. F. Valli, and F. Vega

Copyright © 2014 Cajus G. Diedrich. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

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 “Cretoxyrhina Glickman, 1964”. 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).