Fish can band together, sometimes in the millions, to form a school or shoal. They will move as one, like a flock of birds, so long as each fish stays in line with the fish that surround it.

Modern fish, as well as other kinds of animals, already know how to move as one. But unraveling when in Earth’s deep past this behavior evolved has been a tough fish to fry for scientists.

It’s difficult, for instance, to find evidence of schooling fish in the fossil record. You need just the right circumstances to fossilize something like a school of fish in place within a rock. Then, that rock has to survive intact long enough for a paleontologist to discover it and study it.

But that is just what may have happened.

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