Notiomastodon is an extinct genus of gomphothere proboscidean (related to modern elephants), 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.
Notiomastodon was a generalist feeder capable of consuming various types of plants, which varied according to local environments. In the course of the last glacial period, there was an adaptation towards the consumption of grasses. The genus was originally named in 1929, and has been controversial in the course of taxonomic history as it has frequently been confused with or synonymized with forms called Haplomastodon and Stegomastodon. Extensive anatomical studies since the 2010s have shown that Notiomastodon represents the only valid proboscidean in lowland South America, Haplomastodon is synonymous and Stegomastodon is limited to North America.
Notiomastodon became extinct approximately 11,000 years ago at the end of the Pleistocene epoch. Specimens have been found associated with human artifacts, suggesting that hunting by recently arrived humans may have played a role in their extinction.
Research history
Initial research
Traditionally, several species of gomphotheres from the late Pleistocene in South America were distinguished. These included, on the one hand, a highland form from the Andes, Cuvieronius, whose classification has not been controversial, and, on the other hand, several forms present in the lowlands, such as Haplomastodon and Notiomastodon. In addition to this is Stegomastodon, which has a North American distribution. The relationships of the three genres with each other on their independence or synonymization have been the subject of continuous discussion. The exploration of the South American proboscideans began with the expeditions of Alexander von Humboldt in the transition from the 18th to the 19th century. From his collection of finds, Georges Cuvier published two teeth in 1806, one of which came from the vicinity of the Imbabura Volcano near Quito in Ecuador, and the other from Concepción in Chile. Cuvier did not give them scientific names that are valid today, but simply called the first in French "Mastodon des cordilléres" and the second "Mastodon humboldien". In 1814, Gotthelf Fischer von Waldheim coined for first time scientific names for the South American proboscideans by renaming Cuvier's "Mastodon des cordilléres" as Mastotherium hyodon and "Mastodon humboldien" as Mastotherium humboldtii. Cuvier himself would refer both species to the now-disused genus "Mastodon" in 1824, but created a new name of species for the Ecuadorian find which is "Mastodon" andium (he placed the Chilean find in "Mastodon" humboldtii). From the present point of view, both teeth do not have specific diagnostic characteristics that allow them to be assigned to a species in particular. In the following years, the number of discovered fossils increased, which led Florentino Ameghino in 1889 to give the first general review of the proboscideans in his extensive work on the extinct mammals of Argentina. In this he listed several species, all of which he considered analogous to Cuvier's "Mastodon". In addition to the species already created by Cuvier and Fischer, Ameghino named some new ones, including "Mastodon" platensis, which he had already established a year earlier and whose description was based on a tusk fragment of an adult individual from San Nicolás de los Arroyos in the province of Buenos Aires, on the shores of the Paraná River, (catalog number MLP 8-63). Henry Fairfield Osborn used "Mastodon" humboldtii in 1923 to include it in the new genus Cuvieronius (another genus name he created in 1926, Cordillerion based on "Mastodon" andium, is now considered a synonym of Cuvieronius). Forty years after Ameghino, Ángel Cabrera reviewed the proboscidean finds. He named the genus Notiomastodon, "southern mastodon" and assigned to it the new species Notiomastodon ornatus, of which he had found a mandible and another tusk fragment at Playa del Barco near Monte Hermoso also in Buenos Aires province (catalog number MACN 2157). For his part, he assigned Ameghino's "Mastodon" platensis to Stegomastodon and synonymized this species with some of the names previously proposed by Ameghino. The genus Stegomastodon itself dates back to Hans Pohlig in 1912, who referred it to some findings of North American mandible.