Paleontologist Dana Ehret with the full 6.5-million-year-old fossil of Carcharodon hubbelli. Ehret led the analysis of the impressive fossil, which features a string of shark vertebrae and a jaw full of teeth. Click the photo to see a larger version!
For the last 150 years, paleontologists have debated the origins of the great white shark. Many believe that they descended from the 50-foot megalodon, also known as the megatooth shark (Carcharocles megalodon), which is often imagined to be a vastly inflated great white. But after the discovery of a new fossil species, announced in November 2012, the consensus seems to be shifting. Instead, great white sharks may be more closely related to mako sharks.
The presumed close relation between the megalodon and great white is based on similarities in tooth structure, as both have saw-like edges on their teeth. This may seem like flimsy evidence for such a grand association, but the only evidence that the megalodon lived at all is their enormous teeth, as a cartilage skeleton has never been found.
The new shark fossil (Carcharodon hubbelli), however, is far more complete: it includes several vertebrae and a full jaw with teeth intact. These teeth, like those of the great white and megalodon, are saw-like—but they aren’t as sharp. Instead, they appear to be something in-between the teeth of the mako shark ancestor (Carcharodon hastalis), which are smooth for efficient fish-eating, and the sharp and jagged seal-munching teeth of the great white shark. The hybrid teeth of this new shark fossil provides evidence that this species is the great white shark ancestor, not the megalodon.
In addition, the new fossil shark lived 6.5 million years ago, placing it at a good time to be an intermediate species between the mako shark ancestor and the great white. This combination of evidence supports the hypothesis that great white sharks are a mammal-eating variation on the mako shark, instead of a shrunken-down version of the megalodon.
Reference: DJ Ehret et al. 2012. Origin of the white shark Carcharodon (Lamniformes: Lamnidae) based on recalibration of the Upper Neogene Pisco Formation of Peru. Palaeontology 55 (6): 1139–1153.