Elasmotherium

Elasmotherium (from Ancient Greek ἔλασμα (élasma), meaning "metal plate" with the intended meaning "lamina" in reference to the tooth enamel, and θηρίον (theríon), meaning "beast") is an extinct genus of very large rhinoceros that lived in Eastern Europe, Central Asia and East Asia from the late Miocene through to the Late Pleistocene, until at least 39,000 years ago. It was the last surviving member of the subfamily Elasmotheriinae, a formerly diverse group of rhinoceroses separate from the subfamily Rhinocerotinae, that contains all living rhinoceroses.

Five species are recognised. The genus first appeared in the Late Miocene in present-day China, likely having evolved from Sinotherium, before spreading to the Pontic–Caspian steppe, the Caucasus and Central Asia. Species of Elasmotherium are the largest known true rhinoceroses, reaching body lengths of at least 4.5 metres (15 ft), shoulder heights of over 2 metres (6 ft 7 in), and estimated body masses of 3.5–5 tonnes (7,700–11,000 lb), comparable to an elephant.

The skull of Elasmotherium exhibits a large dome on the top of the skull roof, which is hollow and forms an enlargement of the nasal cavity. No remains of a horn of Elasmotherium have ever been found and the appearance of the horn, if any, has been subject to considerable speculation. Elasmotherium sibericum has often been conjectured and depicted as having borne an enormous nearly 2 metres (6 ft 7 in) long straight horn projecting from the dome. However, a 2021 study found that such a horn was implausible due to the thinness of the outer wall of the dome and the lack of attachment points for a horn on the dome itself, and suggested that the dome (which they proposed was primarily for enhancing the sense of smell) was instead covered by a hard keratinous pad (comparable to the bosses of muskox and African buffalo) and that may have resembled a small horn in mature males.

Later Elasmotherium species are thought to have had a relatively narrow and specialised ecological niche as an inhabitant of the central Eurasian steppe. The high crowned (becoming evergrowing/hypselodont in E. sibiricum, uniquely among rhinoceroses) and complicated enamel pattern of Elasmotherium teeth indicate that they had an abrasive diet of low growing vegetation. Elasmotherium may have fed on grass and/or used its well muscled head to turn over the soil to feed on roots and other subterranean parts of plants.

Due to the widespread assumption that it bore a single elongate horn, Elasmotherium sibiricum has been claimed by some to be the basis of the mythical unicorn (and sometimes consequently nicknamed the "Siberian unicorn"), though the evidence in support of this hypothesis is highly speculative.