Masa Ushioda/Corbis

ScienceShot: The Rise of Jaws

A new analysis of the first fish with the ability to bite is giving paleontologists plenty to chew on. Gnathostomes—vertebrates with jaws, including shark predecessors, the forebears of bony fish (including our own ancestors), and now-extinct lineages such as the armor-plated placoderms—originated between 444 million and 416 million years ago. As reported today in Nature, however, their rise to dominance was more complicated than previously thought. Paleontologists had hypothesized that the evolution of different jaw types, from slicers to crushers, allowed the gnathostomes to rapidly replace jawless fish. But, according to the new study, jawless fish coexisted with gnathostomes for millions of years. It was only after 400 million years ago, when all the major jaw types had been established, that gnathostomes began to take over. Biting may have given the gnathostomes an evolutionary edge, but, like their blood-sucking relative the lamprey, jawless fish hung on for a long time.

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Posted in Plants & Animals, Evolution