Vertebrate fossils from the Jurassic Morrison Formation, Plio-Pleistocene Hagerman Lake Beds, and Oligocene Cypress Hills Formation of western North America, and the Permian Karoo Sequence of South Africa have been found to be radioactive and are radon sources. Radon is an odorless, tasteless, and invisible radioactive gas formed during the decay of uranium. Fossil vertebrates may concentrate the radon precursor, radium, because of its chemical similarities to calcium. Radon daughter elements collect on airborne dust and, if inhaled or ingested, increase the risk of cancer. Good ventilation and prudent handling techniques are recommended in areas where radioactive specimens are present.