Fossilized fish skull shakes up the evolutionary history of jaws

415-million-year-old fossil adds to the growing evidence that sharks are not primitive

Jawed fish tree

Janusiscus schultzei, a 415-million-year-old fish, shared traits with modern sharks and bony fish, suggesting that the common ancestor of both of these aquatic organisms had a bony external skeleton.

K. Trinajstic

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Ancient fish didn’t look like sharks. Because they lack the bony skeleton common in fish like cod and tuna, sharks have always been classified as more primitive and likened to the earliest common ancestor of jawed vertebrates.

CT scans of a 415-million-year-old skull of the early jawed fish Janusiscus schultzei reveal a mix of different fish traits. The top of the skull resembles that of a bony fish, but its inner structure resembles that of a shark. The work, published January 12 in Nature, suggests that from the outside the first jawed vertebrates actually looked like bony fish, and it backs up growing evidence that sharks are not the relics we thought them to be.

Researchers created a virtual model of the Janusiscus skull fossil based on CT scans. Using the model, they were able to investigate the inside of the ancient fish’s skull. The animation above depicts the original fossil and its corresponding 3-D model.

Credit: University of Oxford

Editor’s note: This post was updated on January 16, 2015, to remove the word “outer” from the second sentence. Cod and tuna have a skeleton, not an outer skeleton.

Helen Thompson is the multimedia editor. She has undergraduate degrees in biology and English from Trinity University and a master’s degree in science writing from Johns Hopkins University.

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