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

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 already 50 m.y. ago.

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

“…I. planus (Agassiz), I. xiphodon (Agassiz), (Miocene), I. retroflexus (Agassiz), I. hastalis (Agassiz), and I. escheri (Agassiz), (Miocene-Pliocene) developed in the Miocene, whereas a serration developed from I. hastalis to I. escheri, which is not seen in new discussions as the "ancestor" of the modern white sharks [3]. I. escheri was found only on the Pacific along the South American coastline with extinction in the Pleistocene (Figure 8).…”

“…The change in tooth morphology of Isurus is obviously correlated with a change in feeding habits and prey presence, as already newly described for the Tertiary large shark record (cf. [3]). Isurus seems to have evolved already in the late Early Cretaceous.…”

“…The cusplets were reduced from anterior to posterior changing from a catching to cutting type dentition (see also [11,12]). Serrations were developed twice to Carcharodon and Isurus escheri (after [3]). …”

“…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.…”

“…Macroneoselachians have in most cases ancestors reaching into the upper early or lower Late Cretaceous (e.g., [1][2][3][4][5][6]). 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)).…”