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Environment

Sharks of Eden

By Laura WrightJanuary 2, 2004 6:00 AM

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Seven years ago paleontologist Randall Miller and his colleagues at the New Brunswick Museum in Canada hiked around the small town of Atholville hoping to find a few scattered teeth from prehistoric sea creatures. Instead they stumbled upon a perfectly preserved shark head, now identified as the most ancient intact shark fossil.

The 409-million-year-old species, Doliodus problematicus, was a bottom-dwelling predator that resembled a modern angel shark. One of its unexpected features is a pair of inch-long bony spines protruding from the front edge of the fins, which extended sideways from just behind its head. The spines are similar to those of acanthodians, a group of fish commonly considered more closely related to bony fish than to modern sharks. Such calcified features, never before seen on a shark, blur the evolutionary boundaries between the earliest jawed fishes.

This specimen provides the first evidence that early sharks evolved a complex, predatory jaw-and-tooth structure like that of their modern descendants. The creature possessed a formidable set of 60 scissorslike chompers, designed to tear through the flesh of armored fish. Two rows of partially developed teeth lay in wait behind the functional ones, ready to take the place of a lost tooth.

Even the location of the fossil is a surprise: Many researchers believe sharks evolved along Gondwanaland, an ancient supercontinent, but Doliodus lived near the supercontinent Laurasia, where few shark fossils have previously been found. “The whole discussion of where sharks originated is still up for grabs,” Miller says.

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