The genus Tetralophodon (meaning "four-ridged tooth") was named in the mid-19th century with the discovery of the specialized teeth.
Tetralophodon is suggested to have descended from the "trilophodont gomphothere" Gomphotherium. "Tetralophodont gomphotheres" like Tetralophodon are thought to be ancestral to elephantids and stegodontids,[5] with African species of Tetralophodon suggested to be the ancestor of elephantids.[6]Tetralophodon is also suggested to be the ancestor of the fellow "tetralophodont gomphothere" Anancus.[7]
A large individual of the European species T. longirostris is suggested to have been 3.45 metres (11.3 ft) tall at the shoulder and up to 10 tonnes in weight.[8] The first and second molar teeth are tetralophodont (bearing four pairs of cusps).[9] The mandibular symphysis of the lower jaw 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 (pear-shaped) in cross section.[10][11] The upper tusks are proportionally large,[9] and lack enamel bands.[11]
Distribution
[edit]Fossil skull and tusks of T. longirostris, from Ballestar, Spain at the Museu Geològic del Seminari de Barcelona, Barcelona
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.[9] The likely oldest species in the genus, the European T. longirostris first appeared around 13–12.5 million years ago.[12] 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.[13]
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 (back to front motion) in the lower jaws, akin to that used by modern elephants, but different from that used by earlier gomphotheres.[14]
^Shi-Qi Wang; Haruo Saegusa; Jaroon Duangkrayom; Wen He; Shan-Qin Chen (2017). "A new species of Tetralophodon from the Linxia Basin and the biostratigraphic significance of tetralophodont gomphotheres from the Upper Miocene of northern China". Palaeoworld. in press. doi:10.1016/j.palwor.2017.03.005
^J. Shoshani and P. Tassy. 2005. Advances in proboscidean taxonomy & classification, anatomy & physiology, and ecology & behavior. Quaternary International 126-128:5-20
^J. Shoshani and P. Tassy. 1996. Summary, conclusions, and a glimpse into the future. in J. Shoshani and P. Tassy, eds., The Proboscidea: Evolution and Palaeoecology of Elephants and Their Relatives 335-348
^Mothé D, Ferretti MP, Avilla LS (2016) "The Dance of Tusks: Rediscovery of Lower Incisors in the Pan-American Proboscidean Cuvieronius hyodon Revises Incisor Evolution in Elephantimorpha". PLoS ONE 11(1): e0147009. doi:10.1371/journal.pone.0147009
^Lambert, W. D. (2007). "New tetralophodont gomphothere material from Nebraska and its implications for the status of North American Tetralophodon". Journal of Vertebrate Paleontology. 27 (3): 676–682. doi:10.1671/0272-4634(2007)27[676:NTGMFN]2.0.CO;2. S2CID86332751.
