Was the “Siberian unicorn” really a unicorn?

Do you know Elasmotherium? 4.5 meters long and 2 meters at the withers for a mass of 4 to 5 tons, this cousin of modern rhinos is one of the largest Rhinocerotids known to date. In addition to its extraordinary dimensions, Elasmotherium is mainly known for the unique appearance of its skull.
Drawing of the old view of Elasmotherium caucasium with a single horn questioned today.

Dmitry Bogdanov/Wikimedia, CC BY

One meter long, it is immediately striking by the presence of a gigantic bony dome above the orbits, covered with roughness and traces of powerful blood vessels. A unique aspect among Rhinocerotidae, which led paleontologists, from the end of the 19th century, to propose reconstructions of the animal wearing a gigantic horn in the middle of its forehead. Thus was born the image of the "unicorn of Siberia", even though no fossilized horn of Elasmotherium has ever been found to date… So, did "unicorns" really exist?

Horn, a material that fossilizes poorly

Providing a reliable reconstruction of extinct living beings is one of the main objectives of paleontology, but also one of its most delicate missions. Indeed, the vast majority of fossilized remains available to paleontologists concern the hard and naturally mineralized parts of the organism (shell, skeleton, teeth), the preservation of soft or perishable parts being only possible under conditions of fossilization. very special and fundamentally rare.
Thus, like the skin, hair or scales, the horns of mammals, made up of keratin (like our nails and our hair), most of the time escape fossilization. If the horn of bovids develops on a bony base (called an ankle or horn) which generally fossilizes very well and therefore allows a good approximation of its shape, that of rhinos has a unique structure. Formed of keratin fibers clumped together, rhinoceros horns develop on simple rough areas on the frontal and nasal bones: in the absence of bony ankles, it is therefore very difficult to say precisely the size and shape of the rhinoceros. a rhinoceros horn with only the skull! Thus, apart from a few specific cases such as the woolly rhinoceros, specimens of which have been found frozen in the Siberian soil with their horns, the reconstruction of these appendages in fossil rhinoceros is often very speculative.
White rhinoceros (left) and woolly rhinoceros (right) skulls topped with their horns.

Wikimedia, CC BY

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Who was Elasmotherium, nicknamed the “Siberian unicorn”?
Let's go back to Elasmotherium, one of the most emblematic animals of the Eurasian Pleistocene megafauna (geological period extending from 2.58 million years to 11,700 years before the present). Appeared a little over 2 million years ago in Eurasia, this animal was thought to have disappeared around 200,000 years ago, until a 2018 study reshuffled the cards: the reanalysis of several bone remains from 'Elasmotherium has made it possible to reassess the disappearance of the genus around 39-36,000 years before our era. Our Eurasian Homo sapiens ancestors could therefore have encountered it!

The dog-eared unicorn

A Russian-Ukrainian team, led by Vadim Titov, from the Federal University of Rostov-on-the-Don (Russia), set out, at the end of 2021, to closely re-study the cranial anatomy of Elasmotherium to propose a updated reconstruction of the animal's head. For Titov and his team, the verdict is clear: the bone dome, with very thin walls, was relatively fragile and probably could not support the weight of a 2-meter horn.
The dome must have been covered by a fairly low keratinized area, perhaps pointing slightly backwards. But in any case, the authors of the study exclude the presence of a gigantic horn as usually represented! They also consider the presence of a small keratinized area in the nasal position, which would give Elasmotherium not one but two “pseudohorns” on the skull.
Reconstruction of the head of Elasmotherium proposed by Vadim Titov's team.
Titov et al. 2021, Russian Journal of Theriology, Provided by the author
A new reconstruction which contrasts completely with the image of Epinal that this animal has conveyed for decades, and which could make it lose its nickname of "unicorn"!
Especially since Vadim Titov's team is not the first to propose such a reconstruction for Elasmotherium, since other Russian scientists had already assumed a keratinized dome surmounted by a very small horn from the years 1950-60. A reconstruction that quickly fell into oblivion in favor of a representation certainly much more impressive, but not based on any real evidence.
One of the first representations of Elasmotherium with a very small horn, proposed by VA Teryaev and VA Vatagin in 1934.

V. Zhegallo et al., 2005

If it was not the support of a gigantic horn, what could this dome be used for? The research team sees two main functions in the presence of this strange frontal appendage. By significantly increasing the surface of the nasal mucous membranes, this dome was to provide Elasmotherium with a very powerful sense of smell, no doubt useful for detecting its food, consisting in particular, according to Titov and his team, of buried plant bulbs, as well as grasses growing in the steppes. But this dome was also intended to produce and amplify the sounds emitted by the animal, perhaps for communication purposes during clashes between males or simply daily within groups. However, the authors exclude a direct use in combat as in modern rhinos or mouflons: the very thin bone wall of the dome would probably not have resisted impacts carried out by animals weighing 5 tons!

Parietal representations to be reassessed

This new “tarnished” reconstruction of Elasmotherium could appear disappointing for all those attached to the classic representation of this giant rhinoceros. But in the absence of fossilized horns, it remains arguably the most believable to date.
Nevertheless, associated with the recent reassessment of the disappearance of this animal, the work of Titov and his team makes it possible to better understand the paleoecology of Elasmotherium, and in particular the possible interactions between human groups and this giant rhinoceros. Indeed, if the recent reassessment of the disappearance of Elasmotherium at around 36,000 years ago suggests that Homo sapiens could have crossed these animals, now this new reconstruction allows us to appreciate with a new eye the possible parietal representations of this rhinoceros. atypical.
All eyes are turned in particular to the Russian cave of Kapova, south of the Urals, where strange representations of rhinoceros were sometimes interpreted as those of an Elasmotherium, without certainty: despite the low head and the powerful withers, the horn seemed strangely too short…until today! In the light of this change in the representation of the animal, a multitude of prehistoric works could be reinterpreted in the near future.
Two possible silhouettes of Elasmotherium represented with red ocher in the Russian cave of Kapova, in the Upper Palaeolithic.

V. Zhegallo et al., 2005

In addition, this new reconstruction of Elasmotherium also reminds us that, although the horn is the most symbolic element of the rhinoceros, most of the fossil genera known to date did not have any, or only very small ones! The horn has in fact only appeared in a few lineages over time, and the fact that the 5 current species all bear it should not make us forget that this cranial appendage is more an exception than a rule on the scale of the evolutionary history of rhinos. No matter: even without a gigantic horn, the so-called "Siberian unicorn" remains a fascinating animal whose mysteries are far from having been elucidated.

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