Gomphothere

Gomphothere Temporal range:Late Oligocene-Holocene
Specimen ofGomphotheriumproductumat theAmerican Museum of Natural History
NotiomastodonplatensisCentro Cultural del Bicentenario de Santiago del Estero in Argentina
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Proboscidea
Superfamily:	†Gomphotherioidea
Family:	†Gomphotheriidae (Hay, 1922)A. Cabrera1929
Genera
"Trilophodont gomphotheres" †GomphotheriumBurmeister, 1837 †BlancotheriumMay, 2019 †Gnathabelodon?Barbour & Sternberg, 1935 †Megabelodon?Barbour 1914 †SinomastodonTobienet al., 1986 †RhynchotheriumFalconer, 1868 †CuvieroniusOsborn, 1923 †StegomastodonPohlig, 1912 †NotiomastodonCabrera, 1929 †Eubelodon?Barbour 1914 "Tetralophodont gomphotheres" †Anancus †Paratetralophodon †Pediolophodon †Tetralophodon

Gomphotheresare an extinct group ofproboscideansrelated to modernelephants.First appearing in Africa during theOligocene,they dispersed into Eurasia and North America during theMioceneand arrived inSouth Americaduring thePleistoceneas part of theGreat American Interchange.Gomphotheres are aparaphyleticgroup ancestral toElephantidae,which contains modern elephants, as well asStegodontidae.

While most famous forms such asGomphotheriumhad long lower jaws with tusks, theancestral conditionfor the group, some later members developed shortened (brevirostrine) lower jaws with either vestigial or no lower tusks and outlasted the long-jawed gomphotheres. This change made them look very similar to modern elephants, an example ofparallel evolution.During thePlioceneandEarly Pleistocene,the diversity of gomphotheres declined, ultimately becoming extinct outside of the Americas. The last two genera,Cuvieroniusranging southern North America to western South America, andNotiomastodonranging over most of South America, continued to exist until the end of the Pleistocene around 12,000 years ago, when they became extinctalong with many other megafauna speciesfollowing thearrival of humans.

The name "gomphothere" comes fromAncient Greekγόμφος(gómphos), "peg, pin; wedge; joint" plusθηρίον(theríon), "beast".

Description

Life restoration ofGomphotherium

Life restoration ofCuvieronius,a brevirostrine gomphothere

Gomphotheres differed from elephants in theirtoothstructure, particularly the chewing surfaces on themolarteeth. The teeth are considered to bebunodont,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.Like modern elephants and other members ofElephantimorpha,gomphotheres had horizontal tooth replacement, where teeth would progressively migrate towards the front of the jaws before they were taken the place of by more posterior teeth. Unlike modern elephants, many gomphotheres retained permanent premolar teeththough they were absent in some gomphothere genera.Earlier gomphotheres had lower jaws with an elongatemandibular symphysisand lower tusks, theprimitivecondition for members ofElephantimorpha.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.

Comparison of teeth

• 
  Largely unworn molar ofGomphotherium angustidens,a "trilophodont gomphothere"
• 
  Worn molar ofGomphotherium angustidens
• 
  Molar ofTetralophodon,a "tetralophodont gomphothere"
• 
  Molar of a modern African elephant (Loxodonta) for comparison

Taxonomy

"Gomphotheres" are assigned to their own family, Gomphotheriidae, but are widely agreed to be aparaphyleticgroup. The familiesChoerolophodontidaeandAmebelodontidae(the latter of which includes "shovel tuskers" with flattened lower tusks likePlatybelodon) are sometimes considered gomphotheressensu 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 groupElephantoidea."Tetralophodont gomphotheres" are thought to have evolved from "trilophodont gomphotheres", and are suggested to be ancestral toElephantidae,the group which contains modern elephants, as well asStegodontidae.

While the North American long jawed proboscideansGnathabelodon,EubelodonandMegabelodonbeen assigned to Gomphotheriidae in some studiesother studies suggest that they should be assigned to Amebelodontidae (Eubelodon, Megabelodon) or Choerolophodontidae (Gnathabelodon).

Cladogram ofElephantimorphaafter Li et al. 2023, showing aparaphyleticGomphotheriidae.

Elephantimorpha

Mammutidae(mastodons) Elephantida (gomphotheress.l.) Eritreum Gomphotherium annectens Choerolophodontidae Amebelodontidae(shovel tuskers) "Gomphotheriidae" Gomphotherium angustidens Gomphotherium steinheimense Elephantoidea( "tetralophodont gomphotheres", Elephantidae) Gomphotherium sylvaticum Gomphotherium inopinatum Gomphotherium browni Gomphotherium tassyi Gomphotherium productum+ American gomphotheres

Ecology

Gomphotheres are generally supposed to have been flexible feeders, with the various species having differingbrowsing,mixed feeding andgrazingdiets, 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 maleNotiomastodonindividual suggest that it underwentmusth,similar to modern elephants.Notiomastiodonis also suggested to have lived in social family groups, like modern elephants.

Evolutionary history

Gomphotheres originated in Afro-Arabia during the mid-Oligocene,with remains from theShumaysi Formationin Saudi Arabia dating to around 29-28 million years ago. Gomphotheres were uncommon in Afro-Arabia during the Oligocene.Gomphotheres arrived in Eurasia after the connection of Afro-Arabia and Eurasia during the Early Miocene around 19 million years ago,in what is termed the "Proboscidean Datum Event".Gomphotheriumarrived in North America around 16 million years ago,and is suggested to be the ancestor of later New World gomphothere genera."Trilophodont gomphotheres" dramatically declined during the Late Miocene, likely due to the increasingC₄grass-dominated habitats,while during the Late Miocene "tetralophodont gomphotheres" were abundant and widespread in Eurasia, where they represented the dominant group of proboscideans.All trilophodont gomphotheres, with the exception of the AsianSinomastodon,became extinct in Eurasia by the beginning of thePliocene,along with the global extinction of the "shovel tusker" amebelodontids.The last gomphotheres in Africa, represented by the "tetralophodont gomphothere" genusAnancus,became extinct around the end of the Pliocene and beginning of the Pleistocene.The New World gomphothere generaNotiomastodonandCuvieroniusdispersed into South America during thePleistocene,around or after 2.5 million years ago as part of theGreat American Biotic Interchangedue to the formation of theIsthmus of Panama,becoming widespread across the continent.The last gomphothere native to Europe,Anancus arvernensisbecame extinct during the Early Pleistocene, around 1.6–2 million years agoSinomastodonbecame extinct at the end of theEarly Pleistocene,around 800,000 years ago.From the latter half of the Early Pleistocene onwards, gomphotheres were extirpated from most of North America, likely due to competition withmammothsandmastodons.

The extinction of gomphotheres in Afro-Eurasia has generally been supposed to be the result the expansion of Elephantidae andStegodon.The morphology of elephantid molars being more efficient than gomphotheres in consuming grass, which became more abundant during the Pliocene and Pleistocene epochs.In southern North America, Central America and South America, gomphotheres did not become extinct until shortly after the arrival of humans to the Americas, approximately 12,000 years ago, as part of theLate Pleistocene megafauna extinctionsof most large mammals across the Americas. Bones of the last gomphothere genera,CuvieroniusandNotiomastodon,dating to shortly before their extinction have been found associated with human artifacts, suggesting that hunting may have played a role in their extinction.

External links

• "Buried Treasure in the Sierra Nevada Foothills".Sierra College.Archived fromthe originalon 2019-07-27.Retrieved2014-05-21.(article about a fossil exhibit at the Sierra College Natural History Museum)
• "Gomphothere description including images".Sierra College.Archived fromthe originalon 2019-07-27.Retrieved2014-05-21.
• ""King Tusk" Gomphothere Excavation ".Sierra College.Archived fromthe originalon 2019-07-27.Retrieved2014-05-21.(photos from the excavation of a Gomphothere skeleton on theSierra Collegewebsite)
• "The Gomphotheriidae".University of California Museum of Paleontology.