Stegomastodon

Name: Stegomastodon ‭(‬Roof nipple tooth‭)‬.
Phonetic: Steg-o-mas-toe-don.
Named By: Pohlig‭ ‬-‭ ‬1912.
Synonyms: Mastodon successor,‭ ‬Stegomastodon arizonae,‭ ‬S.‭ ‬texanus,‭ ‬S.‭ ‬rexroadensis.
Classification: Chordata,‭ ‬Mammalia,‭ ‬Proboscidea,‭ ‬Gomphotheriidae.
Species: S.‭ ‬aftoniae,‭ ‬S.‭ ‬mirificus,‭ ‬S.‭ ‬nebrascensis,‭ ‬S.‭ ‬platensis,‭ ‬S.‭ ‬primitivus.
Diet: Herbivore.
Size: Up to‭ ‬2.8‭ ‬meters high at the shoulder,‭ ‬tusks can be up to‭ ‬3.5‭ ‬meters long.
Known locations: North and South America.
Time period: Early Pliocene through to Holocene.
Fossil representation: Multiple specimens.

       A relative of the gomphothere elephants,‭ ‬Stegomastodon along with Cuvieronius was one of only two known elephant genera to spread into South America‭ (‬remains once considered to belong to the Mammut genus are now assigned to these two genera‭)‬.‭ ‬Unlike other gomphothere elephants‭ (‬those like Gomphotherium‭)‬,‭ ‬Stegomastodon only had two tusks that grew down from the upper jaw.‭ ‬Another difference of the tusks is that they curved upwards instead of downwards like in its relatives.
       Stegomastodon and Cuvieronius both appeared in North America first,‭ ‬but the creation of the Isthmus of Panama towards the end of the Pliocene established what is called a‭ ‘‬land bridge‭’ ‬between North and South America.‭ ‬This triggered the Great American Interchange where some North American animals,‭ ‬including these two elephants were able to cross down into South America.‭ ‬However once in South America,‭ ‬Stegomastodon and Cuvieronius diverged into different ecosystems,‭ ‬Cuvieronius into higher and cooler environments and Stegomastodon into warmer lowlands.
       Stegomastodon diverged further into two distinct species,‭ ‬with S.‭ ‬platensis being a browser of vegetation and S.‭ ‬waringi being a grazer of grasses.‭ ‬As a genus however,‭ ‬Stegomastodon was named for the distinctive molar teeth that are high crowned and have a series of ridges and small knobs coated in a layer of thick enamel,‭ ‬perfect for grinding grasses.
       When looking at extinction,‭ ‬Stegomastodon seems to have suffered a similar fate to Cuvieronius.‭ ‬Stegomastodon first disappears from North America during the Pleistocene,‭ ‬but manages to hold on in South America until the Holocene.‭ ‬For a time it seems that Stegomastodon co-existed with early human settlers,‭ ‬but may have been hunted into extinction.‭ ‬Fossil remains of Cuvieronius have been found in association with human habitation and it‭’‬s quite plausible that Stegomastodon would have been used in the same way.

Further reading
- Additional generic and specific stages in the evolution of the Proboscidea. - American Museum Novitates 154:1-5 - H. F. Osborn - 1924.
- The Pleistocene Gomphotheriidae (Proboscidea) from South America. - Quaternary International (Elsevier). 126-128: 21–30 - J. L. Prado, M. T. Alberdi, B. Azanza, B. S�nchez & D. Frassinetti - 2005.
- Population structure of the gomphothere Stegomastodon waringi (Mammalia: Proboscidea: Gomphotheriidae) from the Pleistocene of Brazil - An. Acad. Bras. Ci�nc. vol.82 no.4 Rio de Janeiro. - Dimila Moth�, Leonardo S. Avilla & Gisele R. Winck - 2010.

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