Paleontologists report fossil evidence of coordinated collective motion in a fossilized school of fish of the species Erismatopterus levatus in a study published today (May 29) in the Proceedings of the Royal Society B. The fish lived in the Eocene, about 34–55 million years ago, and seem to follow the rules of not swimming too close to their neighbors or too far away from the pack.
N. Mizumoto et al., “Inferring collective behaviour from a fossilized fish shoal,” P R SOC B, doi:10.1098/rspb.2019.0891, 2019.