A slab of grayish limestone shale from the Eocene Green River Formation, the United States, caught a school of Erismatopterus levatus, an extinct species of freshwater fish. Collective behavior in a school of Erismatopterus levatus. Image credit: Mizumoto et al, doi: 10.1098/rspb.2019.0891. The limestone shale slab, about 22 inches long by 15 inches wide (57 by 37.5 cm), was collected from the Green River Formation, a fossil site located in western...
