In Depth
Palaeocarcharodon seems to have been one of the principal shark genera that appeared in the oceans after the Cretaceous that were now devoid of large marine reptiles. Palaeocarcharodon is often considered to be related to the large Cretaceous shark Cretoxyrhina, however it is the relationship to Carcharodon carcharias (the great white shark) and the giant C. megalodon that interests most researchers.
There is on-going debate as to whether C. megalodon should be placed within the Carcharodon genus with the great white, or within the Carcharocles with the other ‘megatoothed sharks’ such as C. auriculatus, C. chubutensis and C. angustidens (there is also debate as to whether these sharks belong within Carcharodon as well). C. megalodon and Carcharodon carcharias both have distinctive tooth serrations that are very similar to the serrations of Palaeocarcharodon, an observation which leads some to consider Palaeocarcharodon a possible ancestor to these two sharks. However Palaeocarcharodon also has two cusps, smaller points that lie at the base of the main tooth and both C. megalodon and Carcharodon carcharias lack these cusps in their teeth.
The other megatoothed sharks while lacking the serration pattern of Palaeocarcharodon, do have cusps similar to the general Palaeocarcharodon tooth form. To further complicate matters however, another large shark named Otodus is also seen as a potential ancestor to the megatoothed sharks since its teeth have a similar overall form with cusps as well. Perhaps a better area of study would be for the relationship between Palaeocarcharodon and Otodus since the latter first appeared in the Selandian stage of the Paleocene whereas the first Palaeocarcharodon fossils are known from the Danian. In short either of these two genera could be ancestors of the later megatoothed sharks usually attributed to the Carcharocles genus, but as always it is down to how the fossils are studied and interpreted.
If Palaeocarcharodon is the ancestor of C. megalodon and Carcharodon carcharias, then the sequence would be that the tooth serrations of Palaeocarcharodon were lost in the immediate descendants just for them to reappear after the tooth cusps were lost in even later forms. A simpler theory however is that of convergent evolution where C. megalodon and Carcharodon carcharias developed similar serrations to Palaeocarcharodon simply because natural selection favoured those with these similar serrations over those that did not.
Despite the confusion about how Palaeocarcharodon is related to other shark genera, the teeth of this shark remain popular collectors pieces on the fossil market and are regularly offered for sale from specialist stores as well as online sites like eBay.
Further Reading
– Palaeocarcharodon orientalis (SINZOW) (Neoselachii: Cretoxyrhinidae), from the Paleocene of Maryland – Lab. de Pal�ontologie des Vert�br�s. – G. R. Case – 1989.
