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''Paraceratherium'' is an extinct genus of hornless rhinoceros, and one of the largest terrestrial mammals that has ever existed. It lived from the early to late Oligocene epoch (34–23 million years ago); its remains have been found across Eurasia between China and the former Yugoslavia. ''Paraceratherium'' is classified as a member of the hyracodont subfamily Indricotheriinae. ''Paraceratherium'' means "near the hornless beast", in reference to ''Aceratherium'', a genus that was once thought similar. The exact size of ''Paraceratherium'' is unknown because of the incompleteness of the fossils. Its weight is estimated to have been at most; the shoulder height was about , and the length about . The legs were long and pillar-like. The long neck supported a skull that was about long. It had large, tusk-like incisors and a nasal incision that suggests it had a prehensile upper lip or proboscis. The lifestyle of ''Paraceratherium'' may have been similar to that of modern large mammals such as the elephants and extant rhinoceroses. Because of its size, it would have had few predators and a slow rate of reproduction. ''Paraceratherium'' was a browser, eating mainly leaves, soft plants, and shrubs. It lived in habitats ranging from arid deserts with a few scattered trees to subtropical forests. The reasons for the animal's extinction are unknown, but various factors have been proposed. The taxonomy of the genus and the species within has a long and complicated history. Other genera of Oligocene indricotheres, such as ''Baluchitherium'', ''Indricotherium'', and ''Dzungariotherium'' have been named, but no complete specimens exist, making comparison and classification difficult. Most modern scientists consider these genera to be junior synonyms of ''Paraceratherium'', and that it contains four discernible species; ''P. bugtiense'' (the type species), ''P. transouralicum'', ''P. prohorovi'', and ''P. orgosensis'', although the last may be a distinct genus. The most completely-known species is ''P. transouralicum'', so most reconstructions of the genus are based on it. Differences between ''P. bugtiense'' and ''P. transouralicum'' may be due to sexual dimorphism, which would make them the same species. ==Taxonomy== The taxonomic history of ''Paraceratherium'' is complex due to the fragmentary nature of the known fossils and because western, Soviet, and Chinese scientists worked in isolation from each other for much of the 20th century and published research mainly in their respective languages.〔 Scientists from different parts of the world did attempt to compare their finds to get a more complete picture of these animals, but were hindered by politics and wars.〔 The opposing taxonomic tendencies of "lumping and splitting" have also contributed to the problem.〔 Inaccurate geological dating previously led scientists to believe various geological formations that are now known to be contemporaneous were of different ages. Many genera were named on the basis of subtle differences in molar characteristicsfeatures that vary within populations of other rhinoceros taxaand are therefore not accepted by most scientists for distinguishing species.〔 Early discoveries of indricotheres were made through various colonial links to Asia. The first known indricothere fossils were collected from Balochistan (in modern-day Pakistan) in 1846 by a soldier named Vickary, but these fragments were unidentifiable at the time.〔Prothero, 2013. pp. 35–52〕 The first fossils now recognised as ''Paraceratherium'' were discovered by the British geologist Guy Ellcock Pilgrim in Balochistan in 1907–1908. His material consisted of an upper jaw, lower teeth, and the back of a jaw. The fossils were collected in the Chitarwata Formation of Dera Bugti, where Pilgrim had previously been exploring. In 1908, he used the fossils as basis for a new species of the extinct rhinoceros genus ''Aceratherium''; ''A. bugtiense''. ''Aceratherium'' was by then a wastebasket taxon; it included several unrelated species of hornless rhinoceros, many of which have since been moved to other genera.〔Prothero, 2013. pp. 17–34〕 Fossil incisors that Pilgrim had previously assigned to the unrelated genus ''Bugtitherium'' were later shown to belong to the new species.〔 In 1910, more partial fossils were discovered in Dera Bugti during an expedition by the British palaeontologist Clive Forster-Cooper. Based on these remains, Foster-Cooper moved ''A. bugtiense'' to the new genus ''Paraceratherium'', meaning "near the hornless beast", in reference to ''Aceratherium''.〔 His rationale for this reclassification was the species' distinctly down-turned lower tusks. In 1913, Forster-Cooper named a new genus and species, ''Thaumastotherium'' ("wonderful beast") ''osborni'', based on larger fossils from the same excavations, but he renamed the genus ''Baluchitherium'' later that year because the former name was preoccupied, as it had already been used for a hemipteran insect. The fossils of ''Baluchitherium'' were so fragmentary that Foster-Cooper was only able to identify it as a kind of odd-toed ungulate, but he mentioned the possibility of confusion with ''Paraceratherium''. The American palaeontologist Henry Fairfield Osborn, which ''B. osborni'' was named after, suggested it may had been a titanothere.〔 A Russian Academy of Sciences expedition later found fossils in the Aral Formation near the Aral Sea in Kazakhstan; it was the most complete indricothere skeleton known, but it lacked the skull. In 1916, based on these remains, Aleksei Alekseeivich Borissiak erected the genus ''Indricotherium'' named for a mythological monster, the "Indrik beast". He did not assign a species name, ''I. asiaticum'', until 1923, but Maria Pavlova had already named it ''I. transouralicum'' in 1922.〔 Also in 1923, Borissiak created the subfamily Indricotheriinae to include the various related forms known by then. In 1939, Borissiak also named a new species of ''Paraceratherium'' from Kazakhstan, ''P. prohorovi''.〔 In 1922, American explorer Roy Chapman Andrews led a well documented expedition to China and Mongolia sponsored by the American Museum of Natural History. Various indricothere remains were found in formations of the Mongolian Gobi Desert, including the legs of a specimen standing in an upright position, indicating that it had died while trapped in quicksand, as well as a very complete skull. These remains became the basis of ''Baluchitherium grangeri'', named by Osborn in 1923.〔Prothero, 2013. pp. 1–16〕 ''Dzungariotherium orgosensis'' was described in 1973 based on fossilsmainly teethfrom Dzungaria in Xinjiang, northwest China. A multitude of other species and genus namesmostly based on differences in size, snout shape, and front tooth arrangementhave been coined for various indricothere remains. Fossils attributable to ''Paraceratherium'' continue to be discovered across Eurasia, but the political situation in Pakistan has become too unstable for further excavations to occur there.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Paraceratherium」の詳細全文を読む スポンサード リンク
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