Elasmotherium

Elasmotherium("thin plate beast") is an extinct genus of giant rhinoceros endemic to Eurasia during the late Pliocene through the Pleistocene, documented from 2.6 mya to as late 50.000 years ago, possibly later, in the late Pleistocene, an approximate span of slightly less than 2.6 million years. three species were recognized. the best known, E. sibiricum was the size of a mammoth, an is thought to borne a large, thick horn on its forehead which was used for defense, attacking mates, driving away competitors, sweeping snow from grass in winter and digging for water and plant roots. Like all rhinoceroses, elasmotheres were herbivorous. Unlike any others, its high-crowned were ever-growing. Its legs were longer those of other rhinos and were designed for galloping, giving him a horse-like gait. The Russian paleontologist of the 19th century who discovered and named the initial fossils were influenced by ancient legends of a huge unicorn roaming he steppes of Siberia. To date no evidence either contradicts or confirms the possibility that Elasmotherium survived into legendary times. 

http://en.wikipedia.org/wiki/Elasmotherium