Mizumoto wondered whether the fossil he saw had actually preserved the fish in position the very instant they died. He teamed up with a fish-fossil specialist in Japan, and they went back to the museum to photograph the fossil. Then they charted the position and heading direction of every single fish. Mizumoto found that if he looked at where the fish were and where they were going, they seemed to obey two rules that live, modern fish schools follow: repulsion from close neighbors (as if to avoid bumping into one another) and attraction to more distant fish (as if to stay together as a school). Their positions didn’t appear to be random.
“I thought the fossil was fascinating!” James Herbert-Read, an animal-behavior researcher at the University of Bristol, wrote in an email. Scientists look for social rules in live fish by studying their relative positions in photographs; Mizumoto had done the same for long-dead fish but in a fossil. But Herbert-Read still wondered how the fossil could have formed, and whether the fish really had been alive when they were aggregated this way.