Temporal range: 12–.006Ma Miocene - Holocene
|Platybelodon skeleton in a Hubei, China, museum|
†Gnathabelodon Barbour & Sternberg, 1935
The Gomphotheriidae were a diverse taxonomic family of extinct elephant-like animals (proboscideans) — referred to as gomphotheres. They were widespread in North America during the Miocene and Pliocene epochs, 12–1.6 million years ago. Some lived in parts of Eurasia, Beringia and, following the Great American Interchange, South America. Beginning about 5 million years ago, they were gradually replaced by modern elephants, but the last two South American species, in the genus Cuvieronius, did not finally become extinct until possibly as recently as 9,100 BP, and Stegomastodon remains have been dated as recently as 6,060 BP in the Valle del Magdalena, Colombia. Gomphotheres also survived in Mexico and Central America until the end of the Pleistocene.
The name "gomphothere" comes from Greek γόμφος, "peg, pin; wedge; joint" plus θηρίον, "beast".
Gomphotheres differed from elephants in their tooth structure, particularly the chewing surfaces on the molar teeth. Most had four tusks, and their retracted facial and nasal bones prompt paleontologists to believe that gomphotheres had elephant-like trunks. The early gomphotheres, such as Phiomia, had elongated upper and lower jaws, with relatively short tusks. Two lineages appear to have arisen from these ancestors. One, including animals such as Anancus, developed the short lower jaw typical of modern elephants, while the others, including Platybelodon, developed the lower jaw into an elongated 'shovel', and shortened the upper jaw.
The systematics and phylogeny of gomphotheres are unclear and the group might in fact be paraphyletic — i.e., may not include all known descendants of their common ancestor. The genus Gnathabelodon is often placed in its own family, the Gnathabelodontidae, and Archaeobelodon, Protanancus, Amebelodon, Platybelodon and Serbelodon are sometimes regrouped in a separate family, the Amebelodontidae. The genera Anancus, Tetralophodon, Stegomastodon, Paratetralophodon and Cuvieronius are placed by some authors within the gomphotheres, while others consider them as true Elephantidae.
Gomphotheres feeding habits are portrayed as scooping up water plants due to their mandibular tusks which have a shovel like shape. However, this is a misconception because the upper tusks are never taken into consideration. The wear pattern on the mandibular tusks of Platybelodon grangeri and Torynobelodon branumbrowni indicate that these taxa used their tusks to cut through vegetation in a specialized way.
Isotopic analyses for South American gomphotheres suggest a wide dietary for Notiomastodon platensis except for the localities in Santiago del Estero and La Carolina in Ecuador. Isotope analyses suggested an exclusive C4 diet, whereas every other South American locality indicate an exclusive C3 or mixed C3 and C4 diet. The results also support the latitudinal gradient of C3 and C4 grasses. The stereomicrowear analyses for N. platensis exhibited average scratch and pit values, which place it within the extant mixed-feeder morphospace and the higher frequency of fine scratches indicated the ingestion of C3 grasses. Alternatively, the presence of coarse and hypercoarse scratches along with gouges and large pits suggested the ingestion of foliage and lignified portions. The plant microfossil analysis recovered fragments of conifer tracheid and vessel elements with a ray of parenchyma cells, which corroborates the consumption of wood plants, pollen grains, spores, and fibers. The Aguas de Araxa gomphotheres were feeding generalists and consumed wood elements, leaves, and C3 grasses. Cuvieronius specimens from Chile were exclusively C3 plant eaters, whereas specimens from Bolivia and Ecuador had a mixed C3 and C4 diet. Stegomastodon showed a wider range of dietary adaptations. Specimens from Quequen Salado in Buenos Aires Province were entirely C3 feeders, whereas the diet of specimens from La Carolina Peninsula in Ecuador was exclusively C4.
Possible cause for extinction
The results confirm that the ancient diet and diet habits cannot always be interpreted solely from dental morphology or extrapolated from present relatives. The data from middle and late Pleistocene periods point out that over time, there was an adaptive change in dietary resources, away from one that favored predominantly mixed-feeders to more specialized feeders, and that this dietary evolution was one of the contributing causes that forced gomphotheres toward extinction in the late Pleistocene in South America. The remaining population probably succumbed to climatic change and/or human predation around the time of the Holocene margin.
Associations with early human sites
Gomphothere remains are common at South American Paleo-indian sites. Examples include the early human settlement at Monte Verde, Chile, dating to approximately 14,000 years ago, and the Valle del Magdalena, Colombia. In 2011, remains dating between 10,600 and 11,600 years ago were also found in the El Fin del Mundo (End of the World) site in Sonora, Mexico's Clovis location – the first time such an association was found in a northern part of the continent where gomphotheres had been thought to have gone extinct 30,000 years ago. In July 2014, it was announced that the "position and proximity of Clovis weapon fragments relative to the gomphothere bones at the site suggest that humans did in fact kill the two animals there. Of the seven Clovis points found at the site, four were in place among the bones, including one with bone and teeth fragments above and below. The other three points had clearly eroded away from the bone bed and were found scattered nearby." 
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