An off-the-clock project begun on a whim may cause paleontologists and museum curators to rethink their fossil collections. Preserved soft tissue from dinosaurs is limited to a handful of exceptional specimens. In all but the most unusual circumstances, the tissue breaks down quickly after death — even remnant proteins were believed to last a few million years at most. In June, however, researchers reported evidence of blood cells and collagen fibers in poor-quality fossil fragments that...