Gaze into the face of a hagfish—a slimy, eel-shaped marine animal—and the hagfish won’t gaze back. The creatures are almost blind, finding their way around the seafloor primarily using their sense of smell and touch.

Now, in a shock to biologists, a close look at a 300-million-year-old hagfish fossil reveals that the animals once had working eyes—and evolution took them away.

The discovery challenges the way scientists think about the origins of the eye. Living hagfish are remarkably unchanged from their ancient counterparts, and so scientists long thought that modern, sightless hagfish eyes represented a kind of intermediate step between the primitive light-sensing spots in many invertebrates and the camera-like eyes of vertebrates, including humans. (Read “Inside the Eye: Nature’s Most