Evolution of white and megatooth sharks, and evidence for early predation on seals, sirenians, and whales

Cajus G. Diedrich

doi:10.4236/ns.2013.511148

Abstract

The early white shark Carcharodon Smith, 1838 with the fossil Carcharodon auriculatus (Blainville, 1818) and the extinct megatooth shark Otodus Agassiz, 1843 with species Otodus sokolovi (Jaeckel, 1895) were both present in the European proto North Sea Basin about 47.8 - 41.3 m.y. ago (Lutetian, early Middle Eocene), as well as in the Tethys realm around the Afican-Eurasian shallow marine habitats. Both top predators developed to be polyphyletic, with possible two different lamnid shark ancestors within the Early Paleocene to Early Eocene timespan with Carcharodon (white shark line-age) and Otodus (megatooth shark lineage). Their sawblade teeth developed during the early Paleogene as the result of adaptation to feeding on various marine new rising mammals, coinciding with three main waves of evolutionary emergence of seals, sirenians, and whales in parallel with the evolution of these large predatory sharks. Megatooth sharks specialized in hunting whales and sirenians only on the coastal shelves of warm oceans and disappeared globally in the Pleistocene due to climate change and ocean cooling. The cold-water adapted early white sharks have survived until the present day with body temperate change adaptation in warm to temperate oceans and are proposed to have specialized on coastal seal hunting already50 m.y. ago.

Highlights

Large, serrated, fossil shark teeth from Tertiary sediments were generally first attributed to “white shark Carcharodon carcharias (Linné, 1758) ancestors”
Consideration of climate indicators, predator/prey relationships, coevolution of predators and prey, and analyses of dental morphology, combined with access to extensive new material from the Middle Eocene of Europe, has led to the development of the new model presented which differs in many ways to the recently compiled models [16,17], which are not repeated, because they are based on many used primary publications
This new and cladistic model is based on a polyphyletic origin for these two predatory large sharks, which already occupied different ecological niches and had different water temperature preferences by the Middle Eocene (Figure 1)

Summary

Introduction

Large, serrated, fossil shark teeth from Tertiary sediments were generally first attributed to “white shark Carcharodon carcharias (Linné, 1758) ancestors”. Controversy has subsequently arisen whether they should be ascribed to the megatooth shark (“Carcharocles”— Otodus), or to the white shark (Carcharodon) lineage [1]. This controversy is partly a result of non-systematic excavation of single serrated similar looking teeth from many localities around the world, and from horizons of different ages. A single incomplete set of teeth from Carcharodon auriculatus (Blainville, 1818), which is an Eocene relative of the white shark, was illustrated by Storms in 1901 [5]. Tooth sets, or vertebral columns from megatooth sharks have been reported from the Oligocene species Otodus angustidens (Agassiz, 1843) [6,7], as well as from the Miocene species “Otodus turgidus (Agassiz, 1843)” whose latter validity is disputed [5] and, more commonly, from the Miocene to Pliocene species Otodus megalodon (Agassiz, 1843) [8,9]

Methods

Results

Conclusion