The finding, published in the journal Nature, strongly implies that sharks are not the “living fossils” many paleontologists once thought they were. “They have evolved through time to improve upon the basic model,” says John Maisey, a paleontologist at the American Museum of Natural History who helped identify the fossil.

This newly discovered creature dates back 325 million years. It’s no megalodon. It was probably just 2 or 3 feet long and its teeth were tiny, “although there are rows of teeth in the mouth, so it would certainly give you a painful nip,” Maisey says.

The fossil of this beastie is equally modest: It looks like an ordinary brown rock. But in recent years, paleontologists have begun using tools like CT scanners to look inside fossils. When Maisey scanned the fossilized head of the new shark, he got a shock. Inside, “it’s not like the anatomy of a modern shark at all,” he says.