Mastodon Mastodon Mastodons (Greek: μαστός "breast" and ὀδούς, "tooth") are any species of extinct proboscideans in the genus Mammut (family Mammutidae), distantly related to elephants, that inhabited North and Central America during the late Miocene or late Pliocene up to their extinction at the end of the Pleistocene 10,000 to 11,000 years ago. Mastodons lived in herds and were predominantly forest dwelling animals that fed on a mixed diet obtained by browsing and grazing with a seasonal preference for browsing, similar to living elephants. "M. americanum", the American mastodon, is the youngest and best-known species of the genus. They disappeared from
Extinct radionuclide Extinct radionuclide An extinct radionuclide is a radionuclide that was formed by nucleosynthesis before the formation of the Solar System, about 4.6 billion years ago, and incorporated into it, but has since decayed to virtually zero abundance, due to having a half-life shorter than about 100 million years. Short-lived radioisotopes that are found in nature are continuously generated or replenished by natural processes, such as cosmic rays (cosmogenic nuclides), background radiation, or the decay chain or spontaneous fission of very long-lived isotopes such as uranium or thorium. Short-lived isotopes that are not generated or replenished by natural processes are not