Jaws, Teeth of Earliest Bony Fish Discovered

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Two of the new fossils suggest a direct link to bony fish: tooth-bearing jawbones.

What's more, the bones show a tooth pattern that is in between the tooth rows of sharks and bony fishes.

Though these ancient bony fish teeth grew from a bone, old teeth remained attached to the bone. New, larger teeth grew at the inner end of each tooth file.

"It shows a sort of transition between the shark condition and the bony fish condition," Janvier said.

Within 20 million years after Andreolepis hedei and Lophosteus superbus lived, the first bony fish with much larger teeth characteristic of modern bony fish and tetrapods appear in the fossil record. This was during the Devonian period, 416 to 359 million years ago. (Related: "Ancient Fish Fossil May Rewrite Story of Animal Evolution" [October 18, 2006].)

"That's very important because it allowed the bony fishes to become predators," Janvier said.

Sharks also existed in the Devonian, but they were "humble compared to the bony fishes," he said.

The first bony fishes probably ruled the seas, rather than sharks, because the bony fishes' teeth lasted a longer time in the jaw.

"Then, later on, the sharks ... became much larger and big predators," Janvier added.

The study appears in tomorrow's issue of the journal Nature.

Sorting Characteristics

Michael Coates, a biologist at the University of Chicago in Illinois who studies early vertebrate evolution, was not part of the research team.

He said the discovery of rare fossils like the ancient bony fish allows scientists to sort general, primitive characteristics of all jawed vertebrates from the more specialized features that distinguish sharks from bony fishes.

The new study, he noted, clearly shows that Andreolepis and Lophosteus are bony fishes, but their tooth pattern raises a question about what makes a shark a shark.

"Growing teeth in this serial manner around the jaw margin—which once upon a time looked like it was unique to sharks—now looks like it is a general system."

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