Tetralophodon
Tetralophodon, meaning "four", λόφος, meaning "ridge", and ὀδούς is an extinct genus of "tetralophodont gomphothere" belonging to the superfamily Elephantoidea, known from the Miocene of Afro-Eurasia. It has been posited to be the ultimate ancestor of Elephantidae.
Taxonomy and evolution
The type species of Tetralophodon, T. longirostris, was originally named as Mastodon longirostris by Johann Jakob Kaup in 1832, based on remains including a partial mandible with teeth collected from the vicinity of Eppelsheim in Germany. The genus Tetralophodon was later named in 1857 by Hugh Falconer.
Tetralophodon is suggested to have descended from the "trilophodont gomphothere" Gomphotherium, probably a lineage belonging or closely related to the species G. steinheimense. "Tetralophodont gomphotheres" like Tetralophodon are thought to be ancestral to elephantids and stegodontids, with African species of Tetralophodon suggested to be the ancestor of elephantids, with Tetralophodon likely the direct ancestor of the most primitive known elephantid, Stegotetrabelodon. Tetralophodon is also suggested to be the ancestor of the fellow "tetralophodont gomphothere" Anancus.
Description
A large individual of the European species T. longirostris is suggested to have been tall at the shoulder and up to 10 tonnes in weight. The first and second molar teeth are tetralophodont. The mandibular symphysis is typically elongate and bears lower tusks. The lower tusks vary greatly in size and morphology between species, with some species having flattened tusks with an oval-shaped cross section, while others have tusks which are pyriform in cross section. The upper tusks are proportionally large, and lack enamel bands.
Distribution
These animals were very widespread and successful proboscideans. Their fossils have been found from the Middle Miocene to the Late Miocene epochs of Europe, Asia, and Africa. The likely oldest species in the genus, the European T. longirostris first appeared around 13–12.5 million years ago. T. longirostris may have survived in Europe as late as 7 million years ago. The North American species, T. campester and T. fricki, were moved to the genus Pediolophodon in 2007, which is suggested to be unrelated to Tetralophodon, but instead representing parallel evolution.
Ecology
Specimens of Tetralophodon from the late Miocene of East Africa have been suggested to be browsers and mixed feeders based on mesowear analysis. Analysis of tooth wear suggest that these individuals had developed proal movement in the lower jaws, akin to that used by modern elephants, but different from that used by earlier gomphotheres. A similar mixed feeding diet with a strong browsing compotent was inferred for T. longirostris individuals from the Hammerschmiede clay pit in Germany, dating to the early-middle Miocene boundary around 11.4-11.6 million years ago.