Gomphothere

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 following the Great American Interchange. Gomphotheriidae in its broadest sense is paraphyletic and 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.

Gomphothere
Temporal range: Late Oligocene - Holocene
Specimen of Gomphotherium productum at the AMNH
Notiomastodon platensis Centro Cultural del Bicentenario de Santiago del Estero in Argentina
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Proboscidea
Superfamily: †Gomphotherioidea
Family: †Gomphotheriidae
(Hay, 1922) A. Cabrera 1929
Genera

The name "gomphothere" comes from Ancient Greek γόμφος (gómphos), "peg, pin; wedge; joint" plus θηρίον (theríon), "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.[1] 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 fowards stroke from the back to the front) used by modern elephants and stegodontids.[2] Earlier gomphotheres had long lower jaws with lower tusks, similar to other primitive proboscideans. Later members developed shortened (brevirostrine) lower jaws and/or vestigial or no lower tusks.[3]

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" like Platybelodon), were formerly classified as gomphotheres sensu lato, but are now usually considered distinct.[4][5][6] Gomphotheres are divided into two informal groups, "trilophodont gomphotheres", and "tetralophodont gomphotheres". "Trilophodont gomphotheres" are distinguished from "tetralophodont gomphotheres" by the presence of trefoil-shaped wear marks on the occusal surfaces of their teeth,[7] while "tetralophodont gomphotheres" are distinguished by the presence of four ridges on the fourth premolar and on the first and second molars.[4] Some authors choose to exclude "tetralophodont gomphotheres" from Gomphotheriidae, and instead assign them to the group Elephantoidea.[4] "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.[8]

Comparison of teeth

Ecology

Gomphotheres are generally supposed to have mostly been browsers and mixed feeders, though some later species have been inferred to be grazers.[8]

Evolutionary history

Gomphotheres originated in Africa during the Late Oligocene,[9] and arrived in Eurasia after the connection of Africa and Eurasia during the Early Miocene around 19 million years ago,[10] in what is termed the "Proboscidean Datum Event". Gomphotherium arrived in North America around 16 million years ago,[11] and is suggested to be the ancestor of later New World gomphothere genera.[12] "Trilophodont gomphotheres" dramatically declined during the Late Miocene, likely due to the increasing C4 grass-dominated habitats,[10] while during the Late Miocene "tetralophodont gomphotheres" were abundant and widespread in Eurasia.[13] All trilophodont gomphotheres, with the exception of the Asian Sinomastodon, became extinct in Eurasia by the beginning of the Pliocene.[14] The New World gomphothere genera Notiomastodon and Cuvieronius dispersed into South America around or after 2.5 million years ago as part of the Great American Biotic Interchange due to the formation of the Isthmus of Panama.[15] "Tetralophodont gomphotheres" became extinct in Africa around the end of the Pliocene and beginning of the Pleistocene.[16] The last gomphothere native to Europe, the tetralophodont Anancus arvernensis[17] became extinct during the Early Pleistocene, around 2-1.6 million years ago[18][19] Sinomastodon became extinct at the end of the Early Pleistocene, around 800,000 years ago.[20]

The extinction of gomphotheres in Afro-Eurasia has generally been supposed to be the result the expansion of Elephantidae and Stegodon.[14][21] The morphology of elephantid molars being more efficient than gomphotheres in consuming grass, which became more abundant during the Pliocene and Pleistocene epochs.[21] In the New World, gomphotheres did not become extinct until shortly after the arrival of humans to the Americas, approximately 12,000 years ago. Bones of gomphotheres in the Americas dating to shortly before their extinction have been found associated with human artifacts, suggesting that hunting may have played a role in their extinction.[15]

References
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  2. Saegusa, Haruo (March 2020). "Stegodontidae and Anancus: Keys to understanding dental evolution in Elephantidae". Quaternary Science Reviews. 231: 106176. Bibcode:2020QSRv..23106176S. doi:10.1016/j.quascirev.2020.106176. S2CID 214094348.
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