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 eastern 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.
The name "gomphothere" comes from Ancient Greek (), "peg, pin; wedge; joint" plus (), "beast".
Description
Gomphotheres differed from elephants in their tooth structure, particularly the chewing surfaces on the molar teeth. The teeth are considered to be bunodont, that is, having rounded cusps. They are thought to have chewed differently from modern elephants, using an oblique movement (combining back to front and side to side motion) over the teeth rather than the proal movement (a forwards stroke from the back to the front of the lower jaws) used by modern elephants and stegodontids. Earlier gomphotheres had long lower jaws with lower tusks, the primitive condition for members of Elephantimorpha. Later members developed shortened (brevirostrine) lower jaws and/or vestigial or no lower tusks, a convergent process that occurred multiple times among gomphotheres, as well as other members of Elephantimorpha. The incisors and long lower jaws of primitive gomphotheres were likely used for cutting vegetation, while brevirostrine gomphotheres relied on their trunks to acquire food similar to modern elephants.
Taxonomy
"Gomphotheres" are assigned to their own family, Gomphotheriidae, but are widely agreed to be a paraphyletic group. The families Choerolophodontidae and Amebelodontidae (which includes "shovel tuskers" with flattened lower tusks like Platybelodon) are sometimes considered gomphotheres sensu lato, though some authors argue that Amebelodontidae should be sunk into Gomphotheriidae. Gomphotheres are divided into two informal groups, "trilophodont gomphotheres", and "tetralophodont gomphotheres". "Tetralophodont gomphotheres" are distinguished from "trilophodont gomphotheres" by the presence of four ridges on the fourth premolar and on the first and second molars, rather than the three present in trilophodont gomphotheres. Some authors choose to exclude "tetralophodont gomphotheres" from Gomphotheriidae, and instead assign them to the group Elephantoidea. "Tetralophodont gomphotheres" are thought to have evolved from "trilophodont gomphotheres", and are suggested to be ancestral to Elephantidae, the group which contains modern elephants, as well as Stegodontidae.
Ecology
Gomphotheres are generally supposed to have been flexible feeders, with the various species having differing browsing, mixed feeding and grazing diets, with the dietary preference of individual species and populations being shaped by local factors such as climactic conditions and competition. Analysis of the tusks of a male Notiomastodon individual suggest that it underwent musth, similar to modern elephants. Notiomastiodon is also suggested to have lived in social family groups, like modern elephants.