Elasmotherium
Elasmotherium, meaning "metal plate" with the intended meaning "lamina" in reference to the tooth enamel, and θηρίον 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, shoulder heights of over, and estimated body masses of, 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 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 was instead covered by a hard keratinous pad and that may have resembled a small horn in mature males.
Elasmotherium is thought to have had a relatively narrow and specialised ecological niche as an inhabitant of the central Eurasian steppe. The high crowned 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, though the evidence in support of this hypothesis is highly speculative.
Taxonomy
Elasmotherium was first described in 1808-1809 by German/Russian palaeontologist Gotthelf Fischer von Waldheim based on a left lower jaw, four molars, and the tooth root of the third premolar, which was gifted to Moscow University by princess Ekaterina Dashkova in 1807. He first announced the genus name at an 1808 presentation before the Moscow Society of Naturalists, and named the type species E. sibiricum a year later in 1809.The genus name derives from Ancient Greek ἔλασμα, meaning "metal plate", with the intended meaning "lamina", in reference to the laminated folding of the tooth enamel; and θηρίον, meaning "beast" and the species name sibericum is probably a reference to the predominantly Siberian origin of Princess Dashkova's collection. However, the specimen's exact origins are unknown. The specimen narrowly escaped destruction by being evacuated to Nizhny Novgorod during the French invasion of Russia in 1812, when most of the rest of Dashkova's collection was destroyed. The specimen was transferred to the Palaeontological Institute of the Academy of Sciences of the USSR in Moscow during the mid-20th century.
Due to the initially limited known remains and the unique morphology of Elasmotherium, for much of the 19th century its affinities to other mammals were the subject of considerable speculation. Fischer suggested in his original description that Elasmotherium was a "pachyderm which finds a place between elephants and rhinoceroses", while others such as Georges Cuvier in 1817, Anselme Gaëtan Desmarest in 1820, and Richard Owen in 1845 saw it as a "missing link" between rhinoceroses and horses, Henri Marie Ducrotay de Blainville in publications from 1839-1864 suggested that it was an "edentate", and Henri Milne-Edwards in 1868 proposed that it was an aquatic, possibly even marine mammal. Johann Jakob Kaup in 1840-41 was the first author to recognise that Elasmotherium was a rhinoceros, a view followed by Charles Lucien Bonaparte in 1845, who created the group Elasmotheriina to house it. Other authors supporting Elasmotherium as a rhinoceros include George Louis Duvernoy in 1852, who in 1855 erroneously assigned a partial skull correctly attributed to Elasmotherium by Kaup to the new genus and species Stereoceros galli. In 1877, Johann Friedrich von Brandt described the first complete skull of Elasmotherium sibiricum, which put to rest the debate about its affinities and demonstrated unequivocally that Elasmotherium was a rhinoceros.24-25 In 1916, a new genus, Enigmatherium and species E. stavropolitanum were named by Pavlova based on a single tooth found in the Northern Caucasus. This species was later recognised as a synonym of E. fischeri, named by Desmarest in 1820, which itself is now considered a synonym of the type species ''E. sibiricum.''
Evolution
Elasmotherium belongs to the subfamily Elasmotheriinae, distinct from the subfamily which includes all living rhinoceroses, Rhinocerotinae. The depth of the split between Elasmotheriinae and Rhinocerotinae is disputed. Older estimates place the age of divergence around 47 million years ago, during the Eocene, while younger estimates place the split during the Oligocene, around 35-23 million years ago. Unambiguous members of Elasmotheriinae first appeared during the Early Miocene, and the subfamily was speciose and widespread across Europe, Africa and Asia during the Miocene epoch.Cladogram of Rhinocerotidae after Borrani et al. 2025.
Cladogram of Elasmotheriina after Sun et al. 2023:
Elasmotherium is the only known member of Elasmotheriinae to haved survived after the Early Pliocene. with elasmotheriines declining as part of a broader decline of rhinocerotids and many other species of mammals during the late Miocene period. After originating and initially evolving in China during the latest Miocene and Pliocene, Elasmotherium migrated westwards into Central Asia and Eastern Europe around 2.6 million years ago, during the earliest part of the Pleistocene epoch. Elasmotherium became extinct in China by the end of the Early Pleistocene, around 1 million years ago.
Species
The oldest known species of Elasmotherium is Elasmotherium primigenium from the late Miocene of Dingbian County in Shaanxi, China, though some authors have doubted the attribution of this species to Elasmotherium. This species is distinguished from later Elasmotherium species by its more primitive tooth morphology. Like later species, it has the characteristic dome on the skull roof.There are four largely successive species of Elasmotherium aside from the aforementioned E. primigenium, which are—from oldest to youngest—E. chaprovicum, E. peii, E. caucasicum and E. sibiricum, and which together span from the Late Pliocene to the Late Pleistocene. Elasmotherium species are largely distinguished by differences in their tooth anatomy.
Remains of Elasmotherium from the Khaprovian or Khaprov Faunal Complex, which was at first taken to be E. caucasicum, and then on the basis of the dentition was redefined as a new species, E. chaprovicum, named after the Khaprov Faunal Complex. The Khaprov is in the Middle Villafranchian, MN17, which spans the Piacenzian of the Late Pliocene and the Gelasian of the Early Pleistocene of Northern Caucasus, Moldova and Asia and has been dated to 2.6–2.2 Ma. This species is characterised by the relative thickness and roughness of its irregularly folded tooth enamel, its massive metapodial bones, and the morphology of the talus bone of the foot, which are relatively low, have a narrow trochlea and a wide part closest to the tip of the foot. E. chaprovicum may have existed at the same time as early members of E. peii lived in China.
E. peii was first described by Chow, 1958 for remains found in Shaanxi, China. The species is also known from numerous remains from the classical range of Elasmotherium, and some sources have considered this species to be a synonym of E. caucasicum, but it is currently considered distinct. In the western part of its range, it is mainly found in the Psekups faunal complex between 2.2 and 1.6 Ma. In China, E. peii is considered to be the only Pleistocene species of Elasmotherium, spanning from around 2.6 Ma until at least 1.36 Ma, though its remains in China are rare and only known from a handful of localities. This species is distinguished from other Elasmotherium species by several aspects of its dental anatomy, with the teeth being characterised by early closure of the roots, though the roots remain distinct from the crown of the tooth, and several morphological characters of the teeth, including the persistent presence of a postfossette, as well as the shape of the protoloph and metaloph.
E. caucasicum was first described by Russian palaeontologist Aleksei Borissiak in 1914. It is placed as part of the Early Pleistocene Tamanian Faunal Unit. E. caucasicum is more primitive than E. sibiricum and likely represents its direct ancestor. The teeth of E. caucasicum are distinguished from earlier species by their more complex enamel folding, and from E. sibiricum by having larger teeth and a relatively elongate tooth row. E. caucasicum also differs from the later E. sibiricum in some aspects of its limb bone morphology.
E. sibiricum, described by Johann Fischer von Waldheim in 1808 and chronologically the latest species of the sequence appeared in the Middle Pleistocene, ranging northwards to southern-central Russia, westwards into Ukraine and Moldova in Eastern Europe, eastwards into eastern Kazakhstan and southwards to Uzbekistan in Central Asia, and into Azerbaijan in the Caucasus. This species is distinguished from earlier Elasmotherium by having smaller teeth, a reduced number of premolars, open rooted molars, as well as very thin and highly complicated enamel folding in the cheek teeth.