Washington: Although modern Indian and Javan rhinos have a single horn on their noses, the extinct one-horned rhino Elasmotherium was a source of the unicorn legend because it had a two meter-long horn on its forehead and lived with prehistoric humans that drew its image on cave paintings.
All other elasmotheres had a weak or strong nasal horn, whereas Elasmotherium lost its ancestral nasal horn and instead developed a long frontal horn.
Dr. Deng Tao (Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences) and his colleagues reported the first discovered skull of Sinotherium lagrelii from Late Miocene red clays (~7 Ma) of the Linxia Basin, northwestern China.
The transition from a nasal horn to a frontal horn in elasmotheres has been difficult to explain because a major transformational gap exists between nasal-horned ancestors and frontal-horned descendants.
The skull has connected a large posterior nasofrontal horn boss and a smaller frontal horn boss, indicating an intermediate stage to the single frontal horn of Elasmotherium.
Morphological and phylogenetic analyses confirm that Sinotherium is a transitional taxon between Elasmotherium and other elasmotheres.
It is positioned near the root of the giant unicorn clade and originated in a subarid steppe.
A posteriorly shifted nasal horn provides more substantial support and the arched structure of the nasofrontal area is an adaptation for a huge horn.
The S. lagrelii skull provides new information about the origin of the giant unicorn Elasmotherium.