[en] | “Mammut” borsoni

“Mammut” borsoni was first described by American naturalist Isaac Hays in 1834 as Mastodon borsoni, for a tooth discovered near Villanova d’Asti in Piedmont, Italy. It was named after professor Stefano Borson, who had originally attributed the tooth to the species Mastodon giganteum.^[1] Since its description it has been attributed to both the genera Zygolophodon and Mammut (the latter of which contains the American mastodons). The attribution of “M”. borsoni to Mammut has been considered questionable, as the type species for Mammut is known from North America, and there is no evidence there was a migration of Mammut from Eurasia to North America or vice versa, with the similarities between North American Mammut and “M.” borsoni being potentially due to separate parallel evolution from Zygolophodon in Eurasia and North America. Due to the uncertainty, the species continues to be provisionally named “Mammut” borsoni.^[2] Some authors choose to segregate some late Miocene fossils into the species “Mammut” obliquelophus which has molars essentially identical to Pliocene “Mammut” borsoni but the mandibular symphysis of the jaw is somewhat more elongate with larger lower tusks, and the upper tusks are probably shorter.^[3]

“Mammut” borsoni is one of the largest proboscideans known. A 2015 study estimated that some not fully grown specimens from Milia in Greece weighed about 14 tonnes (15.4 short tons) with a shoulder height of 3.9 metres (12.8 ft), with one specimen from the same locality known from an isolated femur estimated to weigh 16 tonnes (17.6 short tons) with a shoulder height of 4.1 metres (13.5 ft); the latter is also estimated to have had been the average size of males of the species. Both of these weight estimates are considerably larger than any known modern elephant, and place it as amongst the largest land mammals to have ever lived.^[4] A fully grown specimen, suggested to be female, from Kaltensundheim, Germany had a shoulder height of 3.2 metres (10.5 ft) and an estimated body mass of 7.8 tonnes (8.6 short tons).^[2] The upper tusks lack enamel bands,^[3] are straight to slightly upwardly curved,^[2] and the longest known amongst proboscideans, with one preserved tusk from Milia measuring 5.02 metres (16.5 ft) in length,^[5][4] with an estimated mass in life of around 137 kilograms (302 lb).^[6] In comparison to earlier mammutids like Zygolophodon, the lower jaw (particularly the mandibular symphysis) is relatively short, but still bears small lower tusks.^[7][2] The jaws appear to have lacked permanent premolar teeth, which are present in more primitive mammutids.^[8] The anatomy of the ulna, radius, femur and foot bones of “Mammut” borsoni are more morphologically similar to those of the American mastodon than to Zygolophodon turicensis, though the converse is true for the humerus and tibia.^[2]

Dental microwear and mesowear analysis of specimens from the Pliocene of Romania and England, respectively, suggest that “M”. borsoni was primarily a browser on leaves and twigs of woody plants.^[9][10] In Pliocene Europe, it coexisted with other proboscidean species, including the mammoth Mammuthus rumanus and the “tetralophodont gomphothere” Anancus arvernensis, which also had browsing-based diets.^[10] Other animals that lived alongside “Mammut” borsoni in the late Pliocene of Europe include the tapir Tapirus arvernensis, the monkey Mesopithecus monspessulanus, the bovine Leptobos stenometopon, the pig Sus minor, the deer Pseudodama lyra, the rhinoceros Stephanorhinus elatus, the sabertooth cat Homotherium crenatidens, the hyenas Pliocrocuta perrieri and Chasmaporthetes lunensis, and the giant cheetah Acinonyx pardinensis.^[11]

“Mammut” borsoni is known from localities across Europe, spanning from the Iberian Peninsula in the west to Ukraine and Greece in the east.^[2] Remains have also been reported from China.^[12] Some authors have suggested that the species derived from Zygolophodon turicensis.^[7] The oldest specimens date to the late Miocene, while the youngest date to the earliest Pleistocene, around 2-2.5 million years ago.^[2]