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Evolution of White and Megatooth Sharks, and Evidence for Early Predation on Seals, Sirenians, and Whales

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Evolution of White and Megatooth Sharks, and Evidence for Early Predation on Seals, Sirenians, and Whales Vol.5, No.11, 1203-1218 (2013) Natural Science http://dx.doi.org/10.4236/ns.2013.511148 Evolution of white and megatooth sharks, and evidence for early predation on seals, sirenians, and whales Cajus G. Diedrich Paleologic, Petra Bezruce 96, Zdice, Czech Republic; [email protected], www.paleologic.eu Received 6 April 2013; revised 6 May 2013; accepted 13 May 2013 Copyright © 2013 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 ments were generally first attributed to “white shark Carcharodon carcharias (Linné, 1758) ancestors”. Con- The early white shark Carcharodon Smith, 1838 troversy has subsequently arisen whether they should be with the fossil Carcharodon auriculatus (Blain- ascribed to the megatooth shark (“Carcharocles”—he- ville, 1818) and the extinct megatooth shark Oto- rein Otodus), or to the white shark (Carcharodon) line- dus Agassiz, 1843 with species Otodus sokolovi age [1]. This controversy is partly a result of non-sys- (Jaeckel, 1895) were both present in the Euro- tematic excavation of single serrated similar looking pean proto North Sea Basin about 47.8 - 41.3 m.y. teeth from many localities around the world, and from ago (Lutetian, early Middle Eocene), as well as in horizons of different ages. DNA studies have at least the Tethys realm around the Afican-Eurasian resolved the general position of the extant form of Car- shallow marine habitats. Both top predators deve- charodon carcharias, placing it between the Isurus and loped to be polyphyletic, with possible two dif- Lamna genera [2,3], without taking into account a revi- ferent lamnid shark ancestors within the Early sion and including of extinct fossil species such as Oto- Paleocene to Early Eocene timespan with Car- dus. The monophyletic evolutionary models that consider charodon (white shark line-age) and Otodus this genus Otodus to be a direct ancestor of the mega- (megatooth shark lineage). Their sawblade teeth tooth sharks [4] have recently received strong support, developed during the early Paleogene as the which can be supported furthermore with new Eocene result of adaptation to feeding on various marine tooth finds from Germany (Figure 1). new rising mammals, coinciding with three main Complete megatooth and white shark skeletons, and waves of evolutionary emergence of seals, sire- nians, and whales in parallel with the evolution even their teeth, are scarce in the Paleocene and Eocene of these large predatory sharks. Megatooth around the world. A single incomplete set of teeth from sharks specialized in hunting whales and sire- Carcharodon auriculatus (Blainville, 1818), which is an nians only on the coastal shelves of warm Eocene relative of the white shark, was illustrated by oceans and disappeared globally in the Pleis- Storms in 1901 [5]. Rare articulated skulls, tooth sets, or tocene due to climate change and ocean cooling. vertebral columns from megatooth sharks have been re- The cold-water adapted early white sharks have ported from the Oligocene species Otodus angustidens survived until the present day with body tem- (Agassiz, 1843) [6,7], as well as from the Miocene spe- perate change adaptation in warm to temperate cies “Otodus turgidus (Agassiz, 1843)” whose latter va- oceans and are proposed to have specialized on lidity is disputed herein [5] and, more commonly, from coastal seal hunting already 50 m.y. ago. the Miocene to Pliocene species Otodus megalodon (Agassiz, 1843) [8,9]. Keywords: Megatooth/White Shark Evolution; The Middle Eocene shark tooth and coprolite-rich [10, Palaeobiogeography; Marine Mammal Coevolution; 11] sites in north-western Germany, which also contain Palaeoecology few marine mammals, recently became important fol- lowing the discovery of the world’s oldest seal remains with a femur and humerus fragment [12], and newest 1. INTRODUCTION sirenians remains with a rib and vertebra fragments [13]. Large, serrated, fossil shark teeth from Tertiary sedi- Only 1% are such mammals, and 99% of the vertebrates Copyright © 2013 SciRes. OPEN ACCESS 1204 C. G. Diedrich / Natural Science 5 (2013) 1203-1218 Figure 1. Global distribution of Middle Eocene (Lutetian) megatooth sharks and white sharks, and their migratory marine mammal prey. Seals were hunted along the beaches of the southern proto North Sea Basin, especially north of Osnabrück (palaeogeography of the Midlde Eocene and important fossil sites of Europe compiled from [10,12,13]). are isolated shark (mostly abundant teeth) and fish re- of finds, which are described herein with focus in the mains [10,11]. Over the past 25 years large quantities of context of predator/prey relationships of marine mam- teeth were sieved from the same layer at two smaller mals-giant sharks, are from a period that is close to the localities (Dalum and Osteroden) near Fürstenau (north- origin of both of these shark genera in the Early to Mid- ern Germany, Figure 1) by two private collectors and dle Eocene Lutetian [14]. more recent the author in a large systematic excavation campaign in 2011 [10]. Both, megatooth sharks and the 2. MATERIAL AND METHODS ancestors of the white sharks have been unearthed from During 2011 Europe’s largest shark tooth excavations gravels with about 2000 specimens. This large amount were completed by the author at two shallow marine fos- Copyright © 2013 SciRes. OPEN ACCESS C. G. Diedrich / Natural Science 5 (2013) 1203-1218 1205 sil sites (Dalum and Osteroden) in north-western Ger- ery of the earliest known (fragmented) seal (herein added many, together with geological and palaeontological a new humerus fragment), sirenian [13] and possible surveys, as an interdisciplinary research project for the whale material (vertebra fragments and rib/longbone Visitor Center at the UNESCO Terra.Vita Geopark/that fragment), which is of great relevance to discussions on built up recently the SharkCenterBippen; German = Ha- the predator-prey relationships, ecology and evolution izentrum Bippen = SCB) [10]. A large total of 180 cubic around the world. meters of conglomeratic material was removed from the The Oligocene material used for comparisons is Dalum forest site for sieving, of which little over 0.1% housed in the Geologische Museum Ostwestfalen-Lippe, (250 × 10 litre buckets) has been sieved to date. A further Dobergmuseum Bünde (GMOL) and the Museum 10 cubic meters were removed from the Osteroden sand Niernstein (MNIE). The Eocene material described pit site, but most of this remains un-sieved. The gravel herein is in the Shark Center, Bippen: German = Haizen- from Dalum was wet-sieved into two size fractions (+4 trum Bippen (SCB) of the Geopark Terra.Vita, and the mm and 4 − 1 mm) and examined for vertebrate, inver- private collection of H. Felker in Ankum (HF). The ma- tebrate, and other fossil remains. At this campaign about terial figured herein is housed all in the SCB. 14.400 fossils (95% are shark teeth) have been found and analysed preliminary only on this public collection of the 3. DISCUSSION Geopark Terra.Vita, including some material of white 3.1. Origin and Evolutionary Model and megatooth teeth [10]. The large private collection owned by H. Felker (in- DNA and cladistic analyses [2,3] have in the past cluded in future in the SCB), which was accumulated failed to provide a satisfactory model for the evolution of over 25 years from these sites with exact stratigraphic Carcharodon and Otodus. However, consideration of context and acribic sorting of all grain sizes (fractiony climate indicators, predator/prey relationships, coevolu- down to 1 mm) ranging over all fossil groups: foramini- tion of predators and prey (such as possible convergent vers to megatooth shark teeth, and terrestrial mammal evolutionary developments), and analyses of dental teeth), was additionally included in this study. This large morphology, combined with access to extensive new amount of material is not to obtain in a short-term exca- material from the Middle Eocene of Europe, has led to vation campaign, and both combined allowed finally the development of the new model presented herein statistical analyses of both collections [10]. Whereas the which differs in many ways to the recently compiled mo- excavation allows clear fossil amounts, the private col- dels [16,17], which are not repeated, because they are lection allows presenting the biodiversity (rare fossils) based on many herein used primary publications. This and analyses of selected species with better amounts. new and not only cladistic model is based on a polyphy- This collection contains approximately 250,000 shark letic origin for these two predatory large sharks, which teeth, about 12,000 fish otoliths [15], many different already occupied different ecological niches and had kinds of macro invertebrate, and vertebrate fossils that different water temperature preferences by the Middle include a few terrestrial mammal teeth and marine mam- Eocene (Figure 1). mal bone fragments [10,12,13]. From this collection, together with the newly excavated material, about 2000 3.2. Evolution-Monophyletic or serrated teeth from Carcharodon and Otodus were sepa- Polyphyletic? rated for this study. Those teeth often are only tooth DNA analyses have placed modern Carcharodon crowns or incomplete teeth without roots which can not white sharks between the Isurus and Lamna lamnid be determined even to the genus. However, this material sharks
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