Chinese mythology holds stories of unicorn-like rhinos, called k’i-lin, inspiring ancient cave paintings that have puzzled scientists for centuries. Other unicorn-like creatures appear in ancient Chinese culture, and the stories have been further adopted in Turkish and Mongolian cultures. But what inspired the stories of these “unicorn” rhinos?
The extinct genus Elasmotherium (a genus endemic to Eurasia during the Late Pliocene through the Pleistocene) was a likely inspiration. The best-known species, E. sibiricum, was the size of a wooly mammoth and boasted a massive six-foot “unicorn horn” on its head. Still, a gap in the fossil record puzzled scientists. The arched nasofrontal structure of Elasmotherium was an adaptation for a posteriorly shifted large horn. Other elasmotheres had a morphologically different horn, located nasally in contrast to the frontal horn of Elasmotherium.
Sinotherium – “Chinese Beast” – was a genus of single-horned rhinoceri of the late Miocene and Pliocene. Previous fossils of Sinotherium lagrelii (a tandem-horned rhino) contained only teeth or cranial and mandibular fragments. This information was enough to place the species taxonomically as a transition species with other related elasmotheres, but left little known about the horn morphology.
Paleontologists from the Chinese Academy of Science in Beijing have now discovered a Sinotherium lagrelii skull which confirms the species as a transition element between Elasmotherium and other elasmotheres – a seven million year old example of an intermediate horn type. Sinotherium had a single horn, similar to the living species Rhinoceros unicornis (Indian rhino) and Rhinoceros sondaicus (Javan rhino). The skull was uncovered in the Late Miocene red clays of the Linxia Basin in northwestern China.
Based on the skull, the nasal horn enlarged gradually and shifted toward the frontal bone in derived elasmotheres. In addition, a smaller frontal horn developed and fused with the nasal horn to form a huge frontal horn.
The S. lagrelii skull has provided a wealth of information. The enlongated skull shape, facial structures, and wrinkled enamel allowed the species to feed on a high-fiber diet of grass. It weighed about 7.7 tons – larger than any known modern-day rhinoceros. Because its size would have caused it to get stuck in wet mud, it likely lived in open, dryer climate in northern China.
Though this finding has helped develop the evolutionary history of the rhinoceros, additional research will continue to fill in the remaining gaps and give a more complete understanding of the story.
Sinotherium lagrelii was described May of this year in the journal Chinese Science Bulletin.
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