Ancient Fish Fossil Sheds Light On Modern Jaws

STEVE INSKEEP, HOST:

OK. Now, this next story is jaw-dropping, in a sense. Scientists in China have unearthed a fossil fish that is the most primitive animal yet discovered that has a jaw.

As NPR's Rhitu Chatterjee reports, the finding throws new light on where our own jaws came from.

RHITU CHATTERJEE, BYLINE: The new fossil is 420 millions years old. It was dug up from a reservoir in China's Yunnan province. Xiaobo Yu works at Kean University in New Jersey, and is a member of the team that studied the fossil.

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XIAOBO YU: Oh, this is such a beautiful specimen. Three-dimensionally preserved.

CHATTERJEE: He says he immediately recognized the fossil's significance.

YU: It's kind of like your adrenaline level goes up, like the feeling of having hit a gold mine.

CHATTERJEE: The specimen belongs to a group of ancient, extinct fishes called Placoderms. It has armored plates on its head and upper body.

YU: So it looks like almost like a small turtle, but with a fish body.

CHATTERJEE: But to Yu's surprise, this fish had a complete upper and lower jaw. Now, mammals, birds, reptiles, amphibians, and bony fishes all have jaws. And scientists know that jaws first appeared in fish.

But they didn't expect to find jaws in this very primitive type of fish. The new discovery suggests jaws may have originated very early on in evolution. The findings are published in the latest issue of the journal Nature.

Matt Friedman is a paleobiologist at Oxford University. He says this early fish didn't have teeth.

MATT FRIEDMAN: But this remarkable creature has an arrangement of bones that looks very much like modern fishes in terms of the composition of the bones that are sort of encircling the mouth.

CHATTERJEE: And these bones are remarkably similar to the bones in our own jaws.

FRIEDMAN: It has what looks like a dentary. It has what looks like a maxilla.

CHATTERJEE: The dentary is the main bone in our lower jaw. And the upper jaw is the maxilla.

FRIEDMAN: This is in a very, very deep part of our own family tree, suggesting that those features we still have are of much greater antiquity than we might have previously thought.

CHATTERJEE: Rhitu Chatterjee, NPR News.

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