Image: Shark
Florida Museum of Natural History illustration by Jason Bourque
This illustration shows what an ancient relative of today's great white sharks may have looked like. A fossil of the specimen, which was larger than modern great whites, suggests great whites are more closely related to mild-mannered mako sharks than to the ancient "megatooth."|
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updated 3/13/2009 2:07:27 PM ET 2009-03-13T18:07:27

A well-preserved fossil of a four- to five-million-year-old great white shark species, complete with 222 sharp teeth, suggests the ocean giants were once even bigger, and that they evolved from the fish-eating relatives of today's mako sharks.

The fossil, excavated at the now-arid Pisco Formation region of Peru, could resolve an ongoing debate among shark experts: Did the great white evolve from so-called "megatooth", or Megalodon, sharks, the largest sharks to ever inhabit the planet, or are they more closely related to modern mako sharks?

It is now clear that the ancient great white species shared habitat with the world's biggest megatooth, Carcharocles megalodon, a 60-foot monster whose jaw may have gaped wider than nine feet. Its megamouth could have been used to investigate, and perhaps swallow, the ancient whales, sea turtles, seals, penguins and even aquatic sloths that shared this part of Peru when it supported a shallow marine environment.

Based on the great white relative's remains, however, the ancient species has been reconstructed "to look very similar to a modern white shark, but also retaining some features of the mako," lead author Dana Ehret told Discovery News.

C. megalodon, in contrast to modern great whites, had ultra-thick teeth with "chevron," or V-shaped, features.

Ehret, a Florida Museum of Natural History researcher, and his colleagues further determined that the prehistoric shark was 20 years old when it died. Like counting growth rings on a tree, the scientists counted light and dark bands in the shark's vertebrae, which calcify with age.

10 deep-sea secrets revealedWhile this particular shark was "only" about 17 feet long — the same length as a respectably sized modern great white — it appears that its close relatives were much bigger.

"We now think that broad-toothed makos and fossil white sharks probably reached lengths upwards of 30 feet in the past, while the largest substantiated [living] white sharks are approximately 21 feet," Ehret said.

As for megatooth sharks, the new study, published in the latest Journal of Vertebrate Paleontology, takes them out of the genus Carcharodon, which megatooths previously were thought to have shared with great whites, and places them in Carcharocles, a group with no known direct living representatives.

"Ehret and his colleagues' work demonstrates a strong evolutionary link between the extinct mako (Isurus hastalis) and the modern great white shark (Carcharodon carcharias) and has concomitantly weakened the classic hypothesis that the modern great white shark evolved from the extinct megatooth shark," shark expert Kenshu Shimada told Discovery News.

Shimada, an associate professor at DePaul University and a research associate in paleontology at the Sternberg Museum of Natural History, believes the genus Carcharocles belongs to the now-extinct family Otodontidae.

"In order to settle the debate over the origin of the modern great white shark and the taxonomy of the megatooth shark, what we now need are the skeletal remains of the megatooth shark and otodontid sharks to examine their evolutionary link," he explained.

Shimada indicated that if megatooths wind up being more closely related to otodontids versus modern great whites, the case can be more fully closed.

"Regardless," he said, "Ehret and his colleagues' work is a very nice example of the provisional nature of science — that is, scientific interpretations change as more data become available."

© 2012 Discovery Channel

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