Notiomastodon is an extinct genus of gomphothere proboscidean, endemic to South America from the Pleistocene to the beginning of the Holocene. Notiomastodon specimens reached a size similar to that of the modern Asian elephant. Like other brevirostrine gomphotheres such as Cuvieronius and Stegomastodon, Notiomastodon had a shortened lower jaw and lacked lower tusks, unlike more primitive gomphotheres like Gomphotherium.

Gomphotheres are an extinct group of proboscideans related to modern elephants. They were widespread across Afro-Eurasia and North America during the Miocene and Pliocene epochs and dispersed into South America during the Pleistocene as part of the Great American Interchange. Gomphotheres are a paraphyletic group that is ancestral to Elephantidae, which contains modern elephants, as well as Stegodontidae. While most famous forms such as Gomphotherium had long lower jaws with tusks, which is the ancestral condition for the group, some later members developed shortened (brevirostrine) lower jaws with either vestigial or no lower tusks, looking very similar to modern elephants, an example of parallel evolution, which outlasted the long-jawed gomphotheres. By the end of the Early Pleistocene, gomphotheres became extinct in Afro-Eurasia, with the last two genera, Cuvieronius ranging from southern North America to western South America, and Notiomastodon having a wide range over most of South America until the end of the Pleistocene around 12,000 years ago, when they became extinct following the arrival of humans.