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Transitional GW Lower

Lower jaw transitional C. carcharias tooth. Chile.

It is difficult to assign transitional teeth to a particular species because the differences between these teeth are not distinct but gradual.

Carcharodon carchariasEdit

Transitional forms of C. carcharias which have only rudimentary serrations. These serrations are present only on the lower parts of the cutting edge, near the crown base, the rest of the cutting edge remaining smooth. Furthermore, there are teeth which are weakly serrate on the complete cutting edge and others which are more or less strongly serrate almost to the crown tip, just a short portion of the tip being smooth-edged. Further there is a difference in the shape of the serrations of the cutting edge. The points of the serration of Carcharodon carcharias are more or less well-developed and mostly directed perpendicular (about 90°) to the cutting edge. The points of the strongly serrate "transitionals", so far as present, are often directed diagonally (angle of around 40°; see e.g. Bourdon (2002), fig. 2, third tooth from left) to the cutting edge and apically directed. These obtusely-oriented serrations in "transitionals" (early to median stage) disappear in late "transitionals" — this further development, means the orientation of the points changed over time.

All the following teeth are from the Bahia Inglesa Formation in Antofagasta, Chile.

A popular hypothesis states that a population of Pacific "Broad-toothed Makos" (broad-form of Cosmopolitodus hastalis), predators of small cetaceans (e.g. dolphins and porpoises) and pinnipeds (elephant seals and sea lions), developed weakly serrate teeth during the Upper / Late Miocene, because flesh is easier to cut with serrate teeth. They could feed effectively, survive better and have more descendants -- establishing this ecological niche in the upper-most Miocene to lower-most Pliocene. This characteristic was passed to descendants and the serrations became stronger over time. The final result was the Great white shark in the Lower / Early Pliocene. In the Early Pliocene, these Great white sharks spread out worldwide as a well-suited predator, prevailing over its own ancestor and all other competitors of a similar ecological niche such as Isurus escheri. Isurus escheri disappeared at the same time in the late Early Pliocene in the eastern North-Atlantic when the Great white shark first appeared there.