Tiny Fish Skull May Be Ancestor of Jawed Vertebrates

The remains of a 415-million-year-old fish skull from Siberia — though miniscule in size — offer hints about the origins of all jawed vertebrates, ranging from reptiles to humans. Researchers originally uncovered the roughly 0.8-inch-long skull in the 1970s, and classified the specimen as a bony fish. There are two main types of living jawed vertebrates: those made of bone and those made of cartilage. Now, a new, more in-depth examination of the ancient fish's brain case shows that the fossil has characteristics of both bony fish, such as salmon and trout, and fish made of cartilage, including sharks and manta rays. The Siberian fossil also suggests that sharks — which are made of cartilage and long thought to be more primitive than bony-jawed vertebrates — are more evolved than had been previously thought.

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