 Complete the following phrase:  Notiomastodon belongs to the family Gomphotheriidae, a group of animals distantly related to modern elephants and mammoths. Notiomastodon seems to have had a 4-million-year-long ghost lineage, diverging from the clade that contains Rhynchotherium and Cuvieronius around the Late Miocene. This would imply that Notiomastodon had been evolving in southern Central America, where the fossils are poorly sampled, prior to its migration into South America during the Pliocene or Pleistocene. Gomphotheres arrived in South America after the formation of the Isthmus of Panama as part of the 