Steppe mammoth

Mammuthus trogontherii, sometimes called the steppe mammoth, is an extinct species of mammoth that ranged over most of northern Eurasia during the Early and Middle Pleistocene, approximately 1.7 million-200,000 years ago. One of the largest mammoth species, it evolved in East Asia during the Early Pleistocene, around 1.8 million years ago, before migrating into North America around 1.5 million years ago, and into Europe during the Early/Middle Pleistocene transition, around 1 to 0.7 million years ago. It was the ancestor of the woolly mammoth and Columbian mammoth of the later Pleistocene.

Taxonomy
There was historically confusion about the correct scientific name for the steppe mammoth, either Mammuthus armeniacus (Falconer 1857) or Mammuthus trogontherii (Pohlig 1885). Falconer described M. armeniacus based on molar teeth collected from near Erzurum in eastern Turkey, of uncertain age, while Pohlig described M. trogontherii from fossil remains found in Europe. A first taxonomical overhaul was done by Maglio (1973) who decided that both names were synonyms, armeniacus being the older, hence the preferred name. However, in Shoshani & Tassy (1996) it was decided that the description of Pohlig prevailed, and consequently the correct name for the steppe mammoth is M. trogontherii. The status of Mammuthus armeniacus as a synonym of Mammuthus trogontherii has been supported by most recent authors. The type specimens of the species are molars from the Süssenborn (also spelled Süßenborn) locality in Germany, dating to the early Middle Pleistocene, (MIS 16, approximately 676-621,000 years ago).

Several Japanese mammoth varieties from the early Pleistocene have been named, but all are now thought to be synonyms of M. trogontherii. The species M. sungari named by Zhou 1959 from specimens found in Zalainuoer, Inner Mongolia, China, that was formerly widely used for mammoths in China is now also recognised as a synonym for M. trogontherii.

Description
Mammuthus trogontherii was one of the largest mammoth species, with males on average being about 4 m tall at the shoulders and about 11 t in weight and females on average being about 3.7 m tall at the shoulders and about 9.5 t in weight, considerably exceeding the size of modern elephants. A largely complete specimen (Zhalainuoer III) from Inner Mongolia, China, was estimated to have had a shoulder height of around 3.69 m measured at the top of the scapula, which represents a flesh shoulder height of 3.89 m, with a body mass estimated via volumetric analysis at 10.4 t. A larger bull, (Azov I), estimated to be 3.96 m tall at the shoulder (previously erroneously estimated as 4.5 m due to incorrect mounting) was estimated to weigh 11.5 t via volumetric analysis. Another individual represented by a single giant humerus 1.46 m long and an associated pelvis found in Mosbach Sande, Germany, is estimated to have had a shoulder height of 4.5 m and a weight of 14.3 t via regression analysis. Steppe mammoths from the late Middle Pleistocene of Europe were considerably smaller than these "typical" M. trogontherii specimens, with the smallest M. trogontherii population being from Stanton Harcourt, England, dating to MIS 7 (around 200,000 years ago), among the last records of the species in Europe, which have an estimated shoulder height of only 2.1-2.9 m. The skull was high-domed and short, and bore twisted tusks. The lower jaw was short and deep. The number of lamellae on the third molars is around 18–22, significantly higher than the number in earlier mammoth species, but noticeably lower than the number typically present in woolly mammoths (M. primigenius), though some European specimens of M. primigenius have counts which overlap with those of M. trogontherii. Compared to M. primigenius, the teeth of calves of M. trogontherii were proportionally larger. The body has around 19 thoracic vertebrae and 5 or 6 sacral vertebrae, with the first few thoracic vertebrae having long neural spines. The tusks were proportionally large, among the largest known among proboscideans, with one large tusk from the Kostolac Basin in Serbia measuring 4.2 m in length, with an estimated mass of 213 kg.

Sequenced genomes suggests that Early Pleistocene M. trogontherii specimens from Siberia, around 1 million years old, had already developed many of the genetic changes thought to be responsible for traits that were adaptations for living in cold environments characteristic of woolly mammoths. Due to the cold climates it inhabited and short tail, Mammuthus trogontherii is suggested to have borne a coat of fur, which was probably somewhat thinner than that of the woolly mammoth.

Distribution and habitat
Fossils of M. trogontherii are known from across northern Eurasia, spanning from Western Europe to Eastern Asia, and into the high latitudes of Northern Asia. Among the southernmost records of the species are known from Taiwan and Miyako Island in the Ryukyu Islands, dating to around 700-500,000 years ago. The species is notably absent from adjacent mainland Southern China. Steppe mammoths were often associated with cold open steppe environments, as its common name would suggest, but was not confined to them, as evidenced by the early Middle Pleistocene West Runton Mammoth specimen from Norfolk, England, which was associated with a temperate forested environment during an interglacial period. In Central Europe, the steppe mammoth was common during glacial periods where it inhabited open landscapes, while remains of steppe mammoths are rare in the more temperate landscapes of Southern Europe.

Ecology
Based on dental microwear analysis, steppe mammoths are thought to have been grazers to mixed feeders, having a similar dietary breadth to Mammuthus meridionalis though considerably more shifted toward grazing on average, and distinct from the predominantly grazing diet inferred for woolly mammoths. The presence of wide scratches on the teeth suggests that steppe mammoths consumed bark and twigs of woody plants (browse), though the proportion of this consumed seems to have varied widely between steppe mammoth populations, with some populations exhibiting browse-dominated mixed feeding, while others consumed little to no browse. The lack of pits on analysed teeth suggests that steppe mammoths did not consume fruit, unlike earlier mammoth species.

Evolution
M. trogontherii is suggested to have derived from Mammuthus meridionalis. The oldest records M. trogontherii are known from China, around 1.7 million years old, from the Nihewan Formation near Majuangou, Hebei. Steppe mammoths arrived in North America across Beringia around 1.5-1.3 million years ago, giving rise to the Columbian mammoth (the ancestor was previously thought to be M. meridionalis but this was due to misinterpretation of tooth wear patterns). Steppe mammoths replaced Mammuthus meridionalis between 1–0.7 million years ago in Europe, in a complex diachronous mosaic pattern, coincident with the arrival of the straight-tusked elephant (Palaeoloxodon antiquus) to Europe. European populations of M. trogontherii experienced progressive size reduction towards the end of the Middle Pleistocene, from around 400,000-300,000 years ago onwards.

The woolly mammoth (Mammuthus primigenius) had emerged in Northeast Siberia from M. trogontherii by around 600-500,000 years ago, reaching the typical molar morphology of M. primigenius around 400,000 years ago. Mammoths with M. primigenius type molar morphology displaced those of M. trogontherii type in Europe over the course of the late Middle Pleistocene, which was largely complete by 200,000 years ago (~MIS 7/6 boundary) in a protracted highly complex pattern including some molars with intermediate morphology between the two species that likely reflects gene flow from Siberian woolly mammoths into European M. trogontherii. Some authors have given remains intermediate between M. trogontherii and M. primigenius the species names Mammuthus intermedius and Mammuthus chosaricus (sometimes Mammuthus trogontherii chosaricus), though the definitions of these supposed species are poorly defined, and some remains attributed to these forms are similar in enamel thickness and lamellar length to "classic" early Middle Pleistocene M. trogontherii. The replacement of European M. trogontherii by woolly mammoths is widely considered to mark the extinction of the species, though some authors have suggested that M. trogontherii survived in northern China and southern Siberia into the Last Glacial Period, and at least one specimen from China has been dated to between 40,000-30,000 years ago.

M. trogontherii is suggested to be the ancestor of the dwarf mammoth species Mammuthus lamarmorai which inhabited the island of Sardinia in the Mediterranean during the late Middle Pleistocene and Late Pleistocene.

Relationship with humans
At the Majuangou site in northern China, a M. trogontherii rib is suggested to display cutting marks. At the Bełchatów coal mine in Poland, dating to the late Middle Pleistocene (in the interglacial period of either MIS 11 or MIS 9, around 425-300,000 years ago), remains of M. trogontherii have been found with cut marks, suggested to represent evidence of butchery by archaic humans, possibly Homo heidelbergensis, though no stone tools were found at the site. Sites with evidence of both humans and M. trogontherii in Europe are rare, especially compared to the contemporaneous straight-tusked elephant, which is suggested to be the result of humans and steppe mammoths primarily occupying different habitats in Europe during the Middle Pleistocene.