(See photos of modern-day sharks.)
Such differences within the same group rock earlier assumptions that a certain set of species with similar characteristics fit in clearly defined categories.
Grouping fish in this way "gives us a coarse picture of evolution," said Brazeau, whose work will appear tomorrow in the journal Nature.
"We need to find intermediaries between groups, find more fossils, and go and see if we've missed some."
(Related: "Odd Fish Find Contradicts Intelligent-Design Argument" [July 9, 2008].)
Biggest Events in History
Michael Coates, a professor of organismal biology at the University of Chicago who was not part of the new study, agreed.
"The common perception is that sharks are somehow primitive relative to bony fish"—foundations that are "sketchy at best," he said.
"It's an important piece in the puzzle for trying to understand one of the biggest events not only in our own evolutionary history, but also the vast majority of living animals with backbones," Coates said.
John Maisey, curator in the division of paleontology at the American Museum of Natural History in New York, was also not involved in the research.
"The classical view that we have two types of jawed vertebrates—bony and shark-like—might be true today, but when you look back at the early fossil record, it becomes more complicated," said Maisey, who also studies early shark-like fish.
"This is the first real movement in this part of the evolutionary tree in the last hundred years."
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