Gomphotherium ("nail beast" for its double set of straight tusks) is an extinct genus of gomphothere proboscidean from the Neogene of Eurasia, Africa and North America. It is the most diverse genus of gompothere, with over a dozen valid species. The genus is probably paraphyletic.

Description

Most species of Gomphotherium were similar in size to the Asian elephant, with G. productum (known from a 35-year-old male) measuring 2.51 m tall and weighing 4.6 t. The largest species G. steinheimense, known from a complete 37-year-old male found in Mühldorf, Germany, measured up to 3.17 m tall and weighed 6.7 t. Gomphotherium, like most basal elephantimorphs, had an elongated lower jaw which bore tusks. Species of Gomphotherium are defined by their conservative molar morphology, which includes "trilophed intermediate molars, third molars with three to four loph(id)s, and pretrite half-loph(id)s typically with anterior and posterior accessory conules that form trefoil-patterned enamel loops with wear (simple molar crowns with no accessory conules on the posttrite side of the crown)".

Ecology

Most species of Gomphotherium are inferred to have been browsers or mixed feeders, but specimens of G. steinheimense from China are suggested to have been grazers. Oxygen and carbon isotopes from G. productum enamel unearthed in the Port of Entry Pit, Oklahoma reveal it fed predominantly on C3 plants year-round.

Evolution

Gomphotherium likely originated in Africa during the late Oligocene-early Miocene. The oldest remains of Gomphotherium are known from Africa, dating to approximately 19.5 million years ago''. Gomphotherium migrated into Eurasia across the "Gomphotherium'' land bridge" approximately 19 million years ago. Gomphotherium underwent rapid evolution after its arrival in Eurasia, reaching its peak diversity during the Early-Middle Miocene. Gomphotherium has been posited to be paraphyletic and the ancestor of later gomphothere genera, including the "tetralophodont gomphotheres" such as Tetralophodon which are probably ancestral to stegodontids and elephantids. Gomphotherium first arrived in North America during the mid-Miocene, approximately 16-15 million years ago, and is suggested to be ancestral to later New World gomphothere genera, such as Cuvieronius, Stegomastodon and Rhynchotherium. Asian populations of Gomphotherium are suggested to have been ancestral to Sinomastodon. The last European species of Gomphotherium became extinct at the beginning of the Late Miocene, around the start of MN9, approximately 10 million years ago. The last Gomphotherium species disappeared from North America at the beginning of the Pliocene, approximately 5 million years ago.

Taxonomy

Species

Over a dozen species of Gomphotherium are considered valid, with over 30 junior synonyms proposed for these taxa. Phylogeny after Wang et al., 2017 Cladogram of Elephantiformes after Li et al. 2023, showing a paraphyletic Gomphotheriidae and Gomphotherium.