Scientists have unearthed the remains of one of the world’s rarest fossils — in downtown Ottawa, Canada. The 450-million-year-old fossil preserves the complete skeleton of a plumulitid machaeridian, one of only 8 such specimens known. Plumulitids were annelid worms — the group including earthworms, bristleworms and leeches, today found everywhere from the deepest sea to the soil in your yard — and although plumulitids were small they reveal important evidence of how this major group of organisms evolved.