This 22 March 2018 video says about itself:
Elasmotherium (“Thin Plate Beast”), also known as the Siberian Unicorn or Steppe Rhinoceros, is an extinct genus of rhinoceros endemic to Eurasia. It lived during the Late Pliocene through the Pleistocene, documented from 2.6 Ma to as late as 29,000 years ago in the Late Pleistocene.
In March 2016, the discovery of a skull in Kazakhstan granted a new estimated time period to when Elasmotherium roamed the earth. The prior estimate was 350,000 years ago, now being reduced to 29,000 years ago. Three species are recognised (some say four).
The best known, E. sibiricum was the size of a mammoth and is thought to have borne a large, thick horn on its forehead. The main difference from other rhinos was the large domed protuberance on the forehead, which was probably a 1.5 meter long and thick horn. Theories about the function of this horn include defense, attracting mates, driving away competitors, sweeping snow from the grass in winter and digging for water and plant roots.
Like all rhinoceroses, elasmotheres were herbivorous. Elasmotherium was a grazer as apparent from tooth wear and morphology. This animal specialized in feeding on grass and underground parts of plants, coastal rivers and lakes, such as highly starchy rhizomes of sedges, cattail and reed.
Unlike any others, its high-crowned molars were ever-growing. Its legs were longer than those of other rhinos and were adapted for galloping, giving it a horse-like gait.
Elasmotherium was the largest member of the family of rhinos that lived from the Pliocene to Pleistocene epochs. It was 6 metres long, 2.5 metres in height and weigh up to 5 tons.
E. caucasicum … reached at least 5 m (16 ft) in body length with an estimated mass of 3.6–4.5 tonnes (4–5 short tons), based on isolated molars that significantly exceed those known from the Siberian species.
Elasmotherium legs are sufficiently like those of the White Rhino to hypothesize a similar gait even though Elasmotherium weighed 4.5-5 ton. Various theories of Elasmothere morphology, nutrition and habits have been the cause of wide variation in reconstruction. Some show the beast trotting like a horse with a horn; others hunched over with head to the ground, like a bison, and still others immersed in swamps like a hippopotamus.
The largest of all the prehistoric rhinoceroses of the Pleistocene epoch, Elasmotherium was a truly massive piece of megafauna, and all the more imposing thanks to its thick, shaggy coat of fur (this mammal was … related to Coelodonta, also known as the “woolly rhino“) and the huge horn on the end of its snout. This horn, which was made of keratin (the same protein as human hair), may have reached five or six feet in length—and if Elasmotherium survived into historical times, it’s possible that early humans glimpsing this huge, strange beast may have been inspired to create the legend of the unicorn.
From Nature Ecology and Evolution, 26 November 2018:
Evolution and extinction of the giant rhinoceros Elasmotherium sibiricum sheds light on late Quaternary megafaunal extinctions
Understanding extinction events requires an unbiased record of the chronology and ecology of victims and survivors.
The rhinoceros Elasmotherium sibiricum, known as the ‘Siberian unicorn’, was believed to have gone extinct around 200,000 years ago—well before the late Quaternary megafaunal extinction event.
However, no absolute dating, genetic analysis or quantitative ecological assessment of this species has been undertaken. Here, we show, by accelerator mass spectrometry radiocarbon dating of 23 individuals, including cross-validation by compound-specific analysis, that E. sibiricum survived in Eastern Europe and Central Asia until at least 39,000 years ago, corroborating a wave of megafaunal turnover before the Last Glacial Maximum in Eurasia, in addition to the better-known late-glacial event.
Stable isotope data indicate a dry steppe niche for E. sibiricum and, together with morphology, a highly specialized diet that probably contributed to its extinction.
We further demonstrate, with DNA sequencing data, a very deep phylogenetic split between the subfamilies Elasmotheriinae and Rhinocerotinae that includes all the living rhinoceroses, settling a debate based on fossil evidence and confirming that the two lineages had diverged by the Eocene. As the last surviving member of the Elasmotheriinae, the demise of the ‘Siberian unicorn’ marked the extinction of this subfamily.