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The experience in reconstructing of the head of Elasmotherium (Rhinocerotidae)

Authors:
  • Southern scientific centre RAS, Rostov-on-Don, Russia
© RUSSIAN JOURNAL OF THERIOLOGY, 2021
Russian J. Theriol. 20(2): 173–182
The experience in reconstructing of the head
of Elasmotherium (Rhinocerotidae)
Vadim V. Titov*, Vera S. Baigusheva & Roman S. Uchytel’
ABSTRACT. We have reconstructed Elasmotherium’s head based on complete intact skulls morphology
analysis. The bony protuberance on the frontal bone was covered with a horny substance that protected the
dome’s relatively thin bones. The keratinized cover grew from the base, clearly visible in the lower part of
the bony dome, and its top was displaced dorso-aborally. The dome’s inner surface was an overgrown nasal
cavity and served to intensify sense of smell, and, possibly, enhance sounds emitted. A relatively small narrow
terminal horn-like cornied pad was attached at nasal and intermaxillary bones’ end, it served to loosen and
dig up soil for lants’ succulent underground parts searching. Powerful muscles were especially prominent
on the neck, they used to carry out lateral and dorsolateral movements of the head.
How to cite this article: Titov V.V., Baigusheva V.S., Uchytel’ R.S. 2021. The experience in reconstructing of
the head of Elasmotherium (Rhinocerotidae) // Russian J. Theriol. Vol.20. No.2. P.173–182. doi: 10.15298/
rusjtheriol.20.2.06
KEY WORDS: Elasmotherium, Pleistocene, appearance reconstruction, skull, muscles, habit of life.
Vadim V. Titov [vvtitov@yandex.ru], Southern Scientic Centre RAS, Chekhov str. 41, Rostov-on-Don 344006, Russia;
Southern Federal university, Rostov-on-Don, Russia; Vera S. Baigusheva, [paleorostov@yandex.ru], Azov Historical,
Archaeological and Paleontological Museum-Reserve, Moskovskaya str. 38/40, Azov 346780, Russia; Roman S. Uchitel’,
[roman.uchytel@gmail.com], Prehistoric Fauna Studio, Klochkivska str., 148 A, Kharkiv 61145, Ukraine.
Опыт реконструкции головы
Elasmotherium (Rhinocerotidae)
В.В. Титов*, В.С. Байгушева, Р.С. Учитель
РЕЗЮМЕ. На основании анализа морфологии нескольких целых черепов Elasmotherium sibiricum
выполнена реконструкция головы эласмотерия. Вздутие лобных костей было покрыто роговым
веществом, защищавшим относительно тонкие кости купола. Роговой слой нарастал от основания,
хорошо заметного в нижней части костного купола, и его верхний конец был смещён дорзо-аборально.
Внутренняя поверхность купола являлась разросшейся носовой полостью и служила обострению
обоняния, и, возможно, усилению издаваемых звуков. На конце носовых и межчелюстных костей
крепилась некрупная узкая терминальная рогоподобная ороговевшая подушка, служившая для рыхле-
ния и раскапывания почвы в поисках сочных подземных частей растений. На шее особо выделялись
мощные мышцы, осуществляющие латеральные и дорзо-латеральные движения головы.
КЛЮЧЕВЫЕ СЛОВА: Elasmotherium, плейстоцен, реконструкция внешнего вида, череп, мышцы,
образ жизни.
* Corresponding author
Introduction
The rhinoceros Elasmotherium is one of the most
enigmatic Eurasian Pleistocene large ungulate. Due
to the peculiar structure of the skull and the dome-
shaped protuberance in the frontal region of the skull,
it is sometimes called the “dome-forehead rhinoceros”
(Teryaev, 1948). Since there are no analogues of this
animal in the modern fauna, there are a number of
reconstructions of this animal appearance, which often
contradict each other. The history of the transformation of
views on the appearance of Elasmotherium is described
in sucient detail in a number of works (Teryaev,
1948; Mazza & Azzarolli, 1993; Zhegallo et al., 2005;
Shvyreva, 2016). The lifestyle of Elasmotherium was
associated with movement in open steppe landscapes
(Flerov, 1953; Svistun, 1973; Shvyreva, 2016) or with a
semi-aquatic lifestyle in near-water stations and overow
lands covered with dense near-water vegetation such as
reed and rush (Teryaev, 1948). Almost all researchers
hold to the point of view of the elasmotherium’s nutrition
174 Vadim V. Titov et al.
in the lower vegetation layer based on the angle of the
plane of the occipital bone with the line of the skull base,
which exceeds 90º and usually amounts to 105–115º
(Shvyreva, 2016). The woolly rhinoceros Coelodonta
antiquitatis Blumenbach, 1799 and the modern white
rhinoceros Ceratotherium simum (Burchell, 1817) have
similar indicators of this character, indicating a low
position of the head in relation to the body.
There is no concurrent view about Elasmotherium’s
feeding’s nature. Brandt (1878a, b) believed that
Elasmotherium were typical herbivores. Some modern
researchers suggest that the features of the teeth of these
animals indicate that they were typical grazers and that
the conversion to a browser type of diet could lead to their
death (Rivals et al., 2020). According to our preliminary
investigations of enamel microwear of E. caucasicum and
E. sibiricum the characters of teeth wearing falls within
the upper limits of variability in herbivores and is close
to mixed feeders animals consuming various types of
vegetation (Baigusheva et al., 2011). However, this type
of dietary analysis does not indicate the specic type of
consumed vegetation. It only determines the amount of
abrasive material and the vegetation layer on which the
animals ate during the period prior to death (Solounias &
Semprebon, 2002). According to these data, a signicant
amount of abrasive material (sand) was present in the food
of the elasmotheriums, more than that of the most part of
grazers. This indirectly testify to the possibility of feeding
of Elasmotherium by the underground parts of plants, too.
Teryaev (1948), supposing a “hippopotamus” way
of life of humpbacks, believed that the basis of their
food was lush greenery and rootstocks of aquatic and
near-water plants. Zhegallo and coauthors (Zhegallo &
Noskova, 2001; Zhegallo et al., 2005) developed this
idea, considering the steppe landscape zone with intra-
zonal near-water biotopes of river oodplains, meadows,
and overgrown ponds to be the habitat of Elasmotherium.
According to these authors, these forage lands used by
the Elasmotherium as preferred feeding places for the
underground parts of aquatic and semi-aquatic plants.
We adhere to the repeatedly expressed point of view
that a number of morphological features (wedge-shaped
structure of the skull with keratinization at the very end
of the snout, large anterior outgrowths of the orbits,
hypsodont teeth, a highly developed sense of smell, sig-
nicant development of the lateral muscles of the neck,
etc.) in conjunction with limbs adapted for movement
on a solid substrate allowed Elasmotherium to actively
feed by underground parts of plants in the zone of open
and semi-open landscapes (Flerov, 1953; Titov, 2008;
Shvyreva, 2016). The study of stable isotopes δ13C and
δ15N from the remains of Elasmotherium sibiricum Fish-
er, 1808 showed that these animals’ diet was markedly
dierent from other Pleistocene rhinoceroses, but it does
not exclude underground non-photosynthetic parts of
plants. It turned out that the values of stable isotopes
δ13C and δ15N in E. sibiricum are most similar to those
in Saiga antelope (Kosintsev et al., 2019).
The origin of the Elasmotherium is rather ancient.
The Elasmotheriinae lineage separated from the other
rhinoceros long ago. This happened presumably in the
Early Oligocene (Antoine, 2002; Shvyreva, 2016) or
even in the Eocene (Kosintsev et al., 2019). During their
independent evolution, Elasmotheriinae have acquired a
number of morphological features that distinguish them
from other representatives of Rhinocerotidae. The genus
Elasmotherium probably appeared in the late Pliocene.
Elasmotherium remains are known within a rather
vast territory — from the North-Western Black Sea
Region to Eastern Asia (Kožamkulova, 1981; Shvyreva,
2016). The most nds of E. sibiricum comes from Western
Siberia and the Northern Caspian Region. However,
most often, the skulls’ cerebral parts are in museum’s
collections. Due to the dome bone’s thinness, the skull
often broke at level of its posterior edge at frontal and
parietal bones’ junction. There are few complete skulls
of this animal. There are no known intact skulls of older
members of the genus (Baigusheva et al., 2018). Finds of
incomplete skulls of E. cf. caucasicum (locality Tokmak,
Zaporozhye Region, Ukraine; collection of the National
Science and Natural History Museum of the National
Academy of Sciences of Ukraine, Kiev; Svistun, 1973)
and E. caucasicum Borissiak, 1912 (locality Sinyaya
Balka, Taman Peninsula, Russia; collection of the Azov
Museum-Reserve) suggest that there are no signicant
dierences in the general morphology of the skull
comparing with that of E. sibiricum.
The Elasmotheriini skull, described from the Late
Miocene locality Dingbian (Shaanxi, NW China),
as a holotype of the new taxon «Elasmotherium
primigenium» (Sun et al., 2021), is not considered in this
article. In our opinion, the taxonomic denition of this
nd is premature. At the same time, it should be noted
that the Late Miocene and Pliocene representatives of
the Tribe (genus Sinotherium) had, in general, similar
characteristics of the skull (Deng et al., 2013), which we
draw attention to in this work.
Materials
The base for the reconstruction were the almost
complete skulls of males E. sibiricum from the Lower
Volga Region (Sarepta locality, Volgograd Region,
Russia; collection of the Natural History Museum (NHM),
London, PV M 12429; Antoine, 2002), Novouzensk
(Saratov District, Bolshoy Uzen’ River, collection of the
Saint Petersburg State Mining Institute (MM) No.57/357
and No.66/357), and Western Kazakhstan (Akzhar
River, Akmolinsk District, Kazakhstan; collection of
the Museum of Zoology of Kazakhtsan (MZK), Almaty;
Tleuberdina & Nazymbetova, 2010), on which the nasal
and premaxillary bones have been preserved (Figs. 1, 2).
We also used skulls with varying degrees of damage, but
they allowed to restore most of the head’s morphology.
They originate from Stavropol Region (Zelenokumsk;
collection of the Stavropol State Museum-Reserve,
Stavropol, No.19907; Shvyreva, 2016), the Lower Volga
Region (collection of the Paleontological institute RAS,
Moscow (PIN); male and female), in particular from
175
The head of Elasmotherium
Fig. 1. Skull of Elasmotherium sibiricum from Western Kazakhstan, Akzhar River, Akmola Region, coll. MZK. A — lateral
view, B — dorsal view, C — rostral view.
Sarepta (collection of the Zoological Institute RAS
(ZIN), Saint Petersburg, No.10792), Verkhniy Kolyshley
(Saratov Regional Local History Museum No. 8470),
and Western Kazakhstan (Atyrau (formerly Guryev);
collection of the V.I. Vernadsky State Geological
Museum, Moscow (GGM) No.32-261 / PV-167).
Due to the deciency of data on detail investigation of
topographic anatomy of head and neck of rhinoceroses,
we used the muscles’ terminology of this body’s part from
the horse’s anatomy (Popesko, 1961). The measurement
were taken by Guerin (1980) and Shvyreva (2016).
Description
A detailed description of the Elasmotherium skulls
and vertebrae is given in some papers (for example,
Svistun, 1973; Shvyreva, 2016). In this work, we focus
on those parts of the skull that allow us to reconstruct
the features of the elasmotherium head.
Skulls are large and elongated. The length of the
skulls of E. sibiricum males (from the localities of Sarep-
ta, Zelenokumsk, Atyrau, Akzhar) reaches 86–89 cm.
The ratio of skull width to length is less than 50%. The
width at lateral occipital tubers reaches 237–380 mm,
and the width of a skull at the level of mastoid bones —
298–486 mm (Shvyreva, 2016; our data). The facial part
of the skull is longer than the cerebral one. The nasal
bones are long, narrow, tapering anteriorly and rostrally
descending below the level of the parietal bones. A solid
bony septum divides the nasal cavity and the dome cavity
into the right and left parts. The thickness of this septum
in the front reaches 32–33 mm, in the posterior direction
it becomes thinner and in the skull’s dome it is 9.6 mm
thick (in specimen from Atyrau).
One of the most important distinguishing features
of the elasmotheriums’ skulls is the presence of a bony
protuberance on the frontal bone, which occupies almost
the entire width of the dorsal part of the skull’s facial
part (except eye orbits). The dome is analogous to the
back horn's basis of the woolly rhinoceros. The size and
shape of the bony protuberance are variable depending
on both sexual and age-related dimorphism. The type of
the roughness of this part of the elasmotherium’s skulls
is very variable. This may indicate dierences in the
shape of the horn structure. The rugosity surface has
hummocky prole with relatively uniform distribution of
bone tubercles (features by Hieronymus et al., 2009). An
evident ring-shaped distribution of rugose’s elements at
the bone dome is not observed. Neurovascular foramens
on the dome surface are no detected. The transition of ru-
gosity to adjacent bone surfaces is inequality at dierent
part of the dome. At the anterior and lateral surfaces of a
dome it has raised edge, and it is smooth at the posterior
part on the transition to parietal bones. This feature is
also variable. For example, at the skull from Akzhar this
raised edges are obviously developed, but at the most
176 Vadim V. Titov et al.
Fig. 2. Skull of Elasmotherium sibiricum from Western Kazakhstan, Atyrau, coll. GGM No.32-261/PV-167. A — lateral view,
B — dorsal view, C — posterior view, D — anterior view, E — dome’s inner part.
part of specimens (from Atyrau and Lower Volga River
Region’s localities) it is weakly marked. On some nds
(for example, on specimen from Akzhar), the roughness
is very markable, while on other skulls, even with large
protuberances, which are attributed to males, the surface
has moderate irregularities. On the female skull from the
PIN collection only slight roughness is visible on the
dome. The roughness on the anterior surface of the dome
is less developed than on the dorsal and posterior parts.
In many specimens, the lower border of the roughness is
clearly visible, it is slightly higher than the dome’s base
in anterior and lateral sides, and in the posterior part
extends to the anterior portion of the parietal bones. In
some nds diagonal grooves are clearly visible on the
aboral part of the place of attachment of the horn struc-
ture in the region of the border of the frontal and parietal
bones, they converge medially with the posterior ends.
The bony protuberance’s diameter at the base ranges
from 25 to 35 cm (depending on the skull’s size). The
thickness of the frontal bone of the dome is 8–9 mm
from anterior, 6–13.5 mm from the lateral (on average,
8.5 mm) and 5–16 mm from posterior sides. Only when
the frontal bone passes to the nasal, lacrimal and parietal
bones its thickness increases.
There are grooves sulci on lateral and partially on
dorsal and posterior surfaces of the dome, it allows to
restore the largest arteries of the domed protuberance
on the skull. In whole, nevrovascular grooves are sparse
and its orientation is anastomosing. The main blood
supply to this part of the skull was carried out by the
dorsal nasal artery arteria dorsalis nasi, which is divided
into branches — the anterior ramus anterior and the
posterior ramus posterior at the orbit’s upper edge level.
The anterior one approaches the dome’s anterior base.
177
The head of Elasmotherium
A vessel branche forward from it, going to the posterior
edge of the nasal notch. Posterior branch a. dorsalis
nasi is subdivided into 3–6 large arteries (their number
may vary in dierent individuals) feeding the lateral,
dorsal and posterior parts of the dome. Grooves from
large vessels are noted not on all specimens at the top
of the protuberance.
The rostral part of the nasal and premaxillary bones
has a well-pronounced roughness, often equipped with
a rounded hook-shaped outgrowth. The width of the
anterior part of nasal bones is rather small and reaches
48–49 mm. The shape of this platform for the attachment
of the horn-like cornied pad is very variable on all
5 known nds with this part of the skull preserved
(Fig. 3). It indicates the variability of the nasal terminal
horn structure. The nasomaxillary notche incisura
nasomaxillaris are high and deep, it indicates a presence
of wide and mobile nostrils.
The partially destroyed lateral wall of the dome
on some nds (in particular, on the skull from Atyrau)
makes it possible to clearly see a structure of the nasal
cavity and the cavity of the dome (Fig. 2E). Inside the
domed protuberance, there are cellular thin-walled
bony outgrowths formed by the frontal concha sinuses
conchalis dorsalis and the maxillary sinuses sinus
maxillaries in anterior, dorsal and lateral parts, as well
as by the labyrinth of the ethmoid bone ethmoturbinalia
in the posterior one (Figs. 4, 5). They form a single
wide-meshed structure, which signicantly increased
the surface of the greatly enlarged nasal cavity and,
accordingly, the mucous membranes. It should be noted
that these internal outgrowths did not form a continuous
structure with internal septa, which could increase the
strength of the bony dome, as can be observed, for
example, in the cavities of the cerebral part of the skull
of elephants.
The eye orbit is limited by well-dened ridges of
frontal, lacrimal and zygomatic bones at the front,
above and below. Especially the orbit’s anterior sides
are limited by powerful outgrowths. The orbit is not
closed from behind.
The parietal bones have a noticeable concavity and
rise considerably towards the occipital ridge. The lateral
parietal ridges are well expressed. They are almost
parallel to each other in the anterior half, but diverge
signicantly in the transition to the occipital part.
The occipital part is low and wide. The upper part
of the occipital bone bifurcates, forming two powerful
lateral occipital tubers, which hang over the occipital
plane and extend beyond the level of the occipital
condyles. The incisures in the occipital ridge is deep.
On its upper edge, the place of nuchal ligament’s
attachment is well expressed. There is a well-dened
roughness for a muscle attachment on the occipital
bone’s nuchal surfaces. The mastoid processes of
the temporal bone processus mastoideus are highly
developed and often protrude beyond the level of the
zygomatic arch and orbit.
The cervical vertebrae of Elasmotherium have a
number of structural features. The rst of them (atlas)
Fig. 3. The shape of the rostral part of the elasmotheriums
skulls: A — Atyrau (coll. GGM No. 32-261 / PV-167), B —
Novouzensk (coll. MM No.57/357), C — Novouzensk (coll.
MM No.66/357); D — Akzhar (coll. MZK), E — Sarepta (coll.
NHM No. PV M-12429).
Fig. 4. Sagittal section of the skull of Elasmotherium sibiricum
from the coll. ZIN (by Shvyreva, 2016).
has transverse processes up to 30 cm long, and has a
range of wings up to 70 cm and exceeds the width of the
skull. An atlas is aproximately twice wider the width of
the skull at lateral occipital tubers and mastoid bones.
The second vertebra (epistropheus) has an elongated
body with a well-dened keel on the ventral surface,
on the sides of which there are deep depressions. Other
cervical vertebrae have high spinous processes, the length
of which increases from the third to the seventh. Long
narrow attened lateral processes are distinguished on
the sixth cervical vertebra (Shvyreva, 2016).
178 Vadim V. Titov et al.
Discussion
The whole skulls, used for the Elasmotherium head’s
external appearance reconstruction, the accumulated data
and conclusions of other researchers, makes it possible
to make some changes to the existing reconstructions.
The point of view of the present paper’s authors
largely coincides with the views of Flerov (1953)
and I.A. Dubrovo and V.D. Kolganоv (exposition
of PIN; Zhegallo et al., 2005), on the habitus of this
animal. We consider a number of ideas of V.A. Teryaev
and V.A. Vatagin (by Teryaev, 1948) concerning
Elasmotherium head’s structural features are deserved
attention.
The muscular system
The skull’s morphology and large muscles insertions
on the skull allow us to restore the head and neck’s
large muscles’ development. Reconstruction of muscles
entire set development degree in this part of the body
is not possible at this stage of the study. Dividing of the
elasmotheriums’ occipital ridge and separation of the
nuchal areas laterally causes some dierent development
of the ligaments and muscles connecting the skull with
the cervical and anterior thoracic vertebrae.
Some semblance of a bifurcated occipital ridge into
two lateral tubers in Elasmotherium is observed in wild
boars, they often break surface layer of the greensward
when searching food. On pigs’ skulls, the lateral parts
of occipital ridge are also deected backward. The well-
pronounced rugosity in the upper part of the incisure in
the occiput of Elasmotherium indicates the attachment
Fig. 5. Transversal section of the skull of subadult individual
of Elasmotherium sibiricum at the level of the posterior part of
the bony dome, coll. Saratov Regional Local History Museum
No. 8470.
of the dorsal raphe of the strongly developed nuchal
occipital ligament ligamentum nuchae. The medial bers
of the trapezius muscle and the intertwined tendons of
the splenius muscle of the head musculus splenius capitis
and the rhomboid minor m. rhomboideus are attached
to it. The nuchal ligament helps to hold the heavy head
and less actively use the muscles of the neck and back,
connecting the head’s back and the spinous processes of
all cervical vertebrae. It is required for running animals,
and accommodates the lowered head in the grazing
position. Bundles of the splenius muscle m. splenius
capitis extend from the tendinous bundles of the nuchal
funiculus attached to the nuchal surfaces under the
occipital lateral tubers.
The occipital bone’s nuchal surfaces, on which
the roughness is expressed, are also the place of
m. semispinalis capitis head semispinal muscle’s
attachment, which connects the skull with the transverse
processes of three-four posterior cervical vertebrae and
ve anterior thoracic vertebrae. The upper fasciculus
of splenius muscle m. splenius capitis is attached to the
well-developed lateral tubers of the occipital crest. It
connects the occiput with the transverse processes of
the rst ve cervical vertebrae, including the alas wings.
Here, the cranial oblique muscle of head m. obliquus
capitis cranialis fasten, which originates at the cranial
edge of the atlas wing. It is possible that the semispinal
muscles of the head m. semispinalis capitis, partially
attached to the lateral parts of the occipital crest, too.
These portions of the muscles facilitated to the spinal
column upper part extension and also pulled the head
back, keeping it in the overturned position.
Elasmotherium has well-dened mastoid processes of
the temporal bone processus mastoideus. They suppose
a signicant development of dorsal band of cervical
muscles: one of the tendinous branches of the longissimus
muscle of a head m. longissimus capitis as well as the head
part of the splenius muscle m. splenius, which go to the
transverse processes of the cervical vertebrae, and also
participates in head’s lateral movements.
In general, the well-developed lateral muscles of the
neck medial and lateral groups allowed the animal to
perform head’s powerful movements in the lateral and
dorsolateral directions in addition to the conventional
dorsoventral ones. In elasmotheriums there is an increase
in the arm of the interaction lever of the rst cervical
vertebra and the skull (occipital tubers and mastoid
bones) in the lateral plane compared to other rhinos. For
example, the width of the atlas of Coelodonta antiquitatis
is 319–391 cm (Garutt, 1998), which is on average almost
twice less than that of Elasmotherium sibiricum.
Keratoid covering of the dome
We think, that the Elasmotherium’s dome was
covered with a keratoid substance that protects this
thin-walled part of the skull, which is vitally important
for animals.
To search for an analogy of the characteristics of
this structure at Elasmotherium, it is logical to look for
it among other rhinos. In modern representatives of the
179
The head of Elasmotherium
Rhinocerotidae, horns are a cornied papillary epidermal
appendages. It is strongly convergent with similar tissues,
such as ungulate hoof wall and bovid artiodactyls horns
(Hieronymus et al., 2006). As mentioned above, the
divergence of the lineage of Elasmotheriinae and other
Rhinocerotidae occurred at the end of the Paleogene
(30–40 million years ago). In Rhinocerotinae, the rst
appearance of derived dermal support of the epidermal
horns is attributed only to the early Miocene (16–20 Ma)
(Hieronymus, 2009). Therefore, it is possible that the
nature of the keratinized cover of the skull’s dome of
Elasmotherium diered from that of other rhinos.
According to Hieronymus (2009) the presence of an
annular (ring-shaped) distribution of rugose bone is one
of the main indicators of a keratinized horns’ presence
on the skull’s bones of rhinos. However, our analysis of
the character of rugosities at the places of attachment
of the horns on the skulls of C. antiquitatis shows that
the obvious ring character is not always observed,
especially on the same of females and young animals.
Here we can observe rather the radial ordering of bone
exostoses, which often coincides with the presence of
bilateral symmetry of the pattern. In general, at known
taxa of rhinos with a clear presence of nasal epidermal
horns there is a compact area on the nasal bones with
a relatively ordered arrangement of elements and often
with annular rugosities. Horn’s basis is a fairly dense
layer of bone. The more developed horn correlates with
more pronounced relief of the rugosity (for example, as
in the male of woolly rhinoceros).
There are dierences in the places of Elasmotheriums
"horns" attachment and horned rhinoceros. The absence
of a clear annular or radial structure of rugosity on the
elasmotherium skull, together with rather thin walls of
the dome, indicates the absence of a epidermal horn on
frontal bones. It should be noted that the presence of
individual variability of the of rugosity’s appearance
and its certain orientation, together with a highly
developed circulatory system, indicates that an epidermal
integumentary pad but not dermal armor was appeared
here. A comparative similarity of the rugose structure is
observed on the frontal boss of african bualo Syncerus
caer, and muskox Ovibos moschatus. In both cases,
the bone that supports the heavily cornied pad of
epidermis is highly vascular and have an uneven surface
(Hieronymus et al., 2009). The dierence is observed
in the presence of rounded knobs on the skull bones of
Elasmotherium, but not depressions.
Some analogy of the growth and development of
such a structure can be found in bovids. It is known
that in Bovidae, for example, in representatives of the
genus Bison, horny sheaths grow on horncores (bony
outgrowths of the frontal bones) gradually, shifting from
the base to the end of the horn. It is known that in modern
rhinos, horn also grows from base (Hieronymus, 2006;
Hieronymus et al., 2006). For this purpose, furrows
and ridges are formed on them, along which the sheaths
growing at the base is shifted. Numerous blood vessels
pass through the cavities in the horncore. They go out and
lie in the canals on the distal half of the horn, providing
active blood supply of the terminal part in area of core
intensive growth. The burr represented by a tubercles’
ring on the core, is located at the place of the keratoid
substance formation. This burr development is more
noticeable on adult males’ horncores. It is poorly
developed in young males and females. With age, a
number of vascular apertures in a core decreases in the
proximal part of a horn. In very old animals’ bone cores’
growth in length stops and their partial resorption occurs.
A number of vascular apertures decreases, and the holes
and channels in the core are closed. The keratoid substance
after the stopping of growth on the horn surface, begins to
chap and peel o, almost does not regenerate. The horn
sheaths in bovids does not correspond to the bone cores
in length. For example, bison’s horny sheaths are longer
than their horncores. The ones of adult animals can be
longer on average by 1/3 of their bony base (Sokolov,
1979: pp. 31–32).
The presence of varying degrees of rugosity’s rate
on the surface of the bone’s dome in Elasmotherium
indicates an individual, age and sexual variability of
the cornied pad. We can assume that in young, very
old individuals and females, the dome was covered with
a relatively thin keratin layer. It is logical to assume a
greater degree of development of this structure in adult
males. The presence of diagonal grooves on the aboral
part of the rugosity surface, partially extending from the
back of the dome-shaped protuberance to the parietal
bones, may indicate that the upper end of the more
developed pad was displaced dorso-aborally. Indirect
evidence of the presence of a relatively thin keratin
layer of the dome is a trace of intravital damage on the
anterio-lateral surface of the dome at the skull from Atyrau
(Fig. 1). This hole with traces of overgrowth is interpreted
as a injury’s consequence (Zhegallo et al., 2005).
Bone dome
The Elasmotherium dome surface is covered
with roughness. But the degree of its intensity can
vary individually, as, for example, at the attachment
points of horns in woolly rhinoceros. But, at the same
time, the degree of development of this roughness in
Elasmotherium is never as strong as, for example, in
woolly rhinoceros. The dome cavities, being a widening
of the nasal cavity, in addition to enhancing the sense
of smell (as pointed out by many researchers of
Elasmotherium) could also function as sounds amplier.
We observe that the dome greatest development occurs
for adult males. On young animals’ skulls and on the
skull from the collection of the PIN, which is attributed
to the female (Zhegallo et al., 2005; Shvyreva, 2016),
the dome cavity is not so hypertrophied. Probably, a
relatively small widening of this cavity was enough
for elasmotherium for normal life. For males, to attract
females and control of the territory, it was necessary to
reproduce louder sounds, which were amplied with the
help of a volumetric dome. In addition to protecting the
thin-walled bone dome from mechanical inuences, the
overgrown keratoid pad in Elasmotherium could also
serve to protect the neck from the attack of predators.
180 Vadim V. Titov et al.
Rostral part of the skull
The presence of a solid internasal septum in
Elasmotherium suggests signicant loads at the muzzle
end. Despite the fact that recent rhinos are also capable
of producing signicant eects with the nasal horns, their
internasal septum remains cartilaginous throughout their
life (Garutt, 1998). A similar development of internasal
septum is characteristic for woolly rhinoceros, which had
a large anterior horn, used as well as for shoveling snow
and an upper layer of greensward. At the anterior end of
the nasal and intermaxillary bones of the Elasmotherium,
there are clearly visible thickenings with a rough surface,
which suggest the attachment of small and narrow horn
formations to them. Taking into account the supposed
active use of the end of the muzzle for raking and digging
a soil to nd underground parts of plants, it is possible
that a horn was used for this purpose. In Teryaev (1948),
on reconstructions the nasal horn is displaced dorsally
rather high, like for recent rhinos. Brandt (1878b)
suggested the presence of a small nasal horn, located
at the muzzle tip and representing a low keratoid plate.
However, on the Rashevsky’s engraving, supervised
by Brandt, such a horn almost did not discernible. The
authors know about ve skulls with intact rostral part
(Fig. 3), their analysis allows us to clarify the anterior
horn-like conformation’s position. The development of
variable in shape thickenings and rounded hook-shaped
bony outgrowths on the rostral part of the intermaxillary
bones suggests the location here of a small terminal horn-
like structure. The nasal bones tip, slightly protruding
above the intermaxillary bones, probably acted as an
upper stop for this “horn”.
There are no annular distribution of rugose bone on
the anterior part of the nasal bones and on the terminal
part of the internasal septum. This indicates the absence
of true epidermal horns. Roughness on the anterior part of
the nasal bones indicates the presence of a cornied pad
or cornied sheath, as well as for a keratinized covering
of the dome at the frontal bones. Taking into account
the dierent degree of the rugouse area development
and the presence of bony “hooks” on the anterior edge
of the internasal septum, we can assume the variable of
shape and size of this terminal cornied pad, regardless
of gender. The presence of pronounced bony “hooks”
(for example, on the skull from Atyrau) suggests that
they were a support for the horn-like structure of the
cornied pad in adult individuals.
The presence of roughness on the nasal bone anterior
part and the rostral part of the internasal septum also
suggests the presence of a movable eshy upper lip,
which is necessary for digging out tubers and rootstocks.
Food base
Teeth of elasmotheriums have a sidewall hypsodonty
with the highest crown height among ungulates. On
the permanent teeth of Elasmotherium sibiricum roots
did not formed at all, even on premolars, and in the
Early Pleistocene E. caucasicum roots on M2 and
M3 are unknown also. Such hypsodont teeth suggests
intake of a highly abrasive food. Recently, more and
more researchers adhere to the point of view that
underground parts of plants were the nutrition basis for
Elasmotherium. It is a food resource poorly consumed
by other animal species. In contrast to the opinion of
Teryaev (1948) and Zhegallo et al. (2005), we believe
that these animals harvested bulbs, tubers, or rootstocks
not so much in shallow parts of water bodies as in other
biocenoses. Steppes, forests and meadows are the phyto-
communities rich by ephemeroids (perennial herbaceous
plants with underground succulent organs). Probably,
seasonality in the change of places for obtaining food
was characteristic for elasmotheriums. It is also possible
that the diet of these animals included aboveground parts
of herbaceous plants and shrubs in smaller quantity.
Based on the characteristics noted, the head
of Elasmotherium was reconstructed (Fig. 6). The
skulls and mandibles of E. sibiricum were taken as a
basis. The pelage, which was present on the head of
representatives of this species most likely, was not taken
into account in the gures presented in order to detail
some morphological features. Taking into account that
the roughness is much more developed on the posterior
part of the bony dome and on the adjacent parts of the
parietal bones, and the posterior portion of the blood
vessels on the dome is more pronounced, we assume
that the keratoid substance was more developed precisely
on the posterior half of the dome-shaped protuberance.
Probably, the uneven growth of the keratoid substance
led to the displacement of the apex of the horny sheaths
in the dorsal-aboral direction.
Conclusions
Representatives of the genus Elasmotherium have
no analogues in the modern fauna. Elasmotheriinae
separated from other branches of the Rhinocerotidae
family more than 30 million years ago. During this period
of evolution they acquired a number of morphological
and physiological features. Therefore, during the
reconstructing the external appearance of elasmotherium,
one cannot fully rely on that of recent rhinoceroses
or other well-studied fossil taxa (for example, woolly
rhinoceros). Both the late Middle Pleistocene Siberian
elasmotheriums and Early Pleistocene Caucasian ones
had a wedge-shaped form of the anterior part of the
skull with a small "horn" at the very end of the muzzle,
well-dened anterior outgrowths of the orbits, hypsodont
teeth, large olfactory lobes of the brain, hypertrophic
nasal cavities, a highly developed sense of smell, and
signicant development of the lateral muscles of the
neck. We adhere to the point of view of researchers
who believed that the characteristics of the skulls and
necks of elasmotheriums indicate adaptations to digging
out from the soil and feeding by underground parts of
plants. Bulbs, tubers, and rootstocks of perennial plants in
steppes, meadows, and forest areas probably constituted
a signicant part of the diet of these large animals, which
have occupied an unoccupied ecological niche. This
allowed the Elasmotherium to exist from the end of
the Pliocene to the late Pleistocene without any special
181
The head of Elasmotherium
Fig. 6. Reconstruction of the head of male of Elasmotherium. Author R.S. Uchitel’.
morphological rearrangements. Late Elasmotherium
diered from the early Pleistocene forms only by slightly
smaller sizes, minor changes in the dentition, and, most
likely, in the presence of a coat.
One of the main distinguishing features of these
distinctive rhinos is a dome-shaped bony protuberance
on the frontal bones, which causes major controversy
among scientists and restorers. The thin walls of the bony
dome in anterior, lateral and dorsal sides have an average
thickness of about 1 cm. The wide-meshed structure
inside the dome, formed by overgrown thin-walled
bony outgrowths of the frontal concha and maxillary
sinuses, as well as the labyrinth of the ethmoid bone is
not a structure of strengthening of the dome strength.
This makes it possible to assume that the dome was
not a place of attachment of a large horn or any other
structure, but was covered with a relatively thin keratoid
substance, which mainly performs a passive protective
function for fragile bones. The dome inner surface was
an overgrown nasal cavity, which served to intensify a
sense of smell, and, possibly, to amplify sounds emitted.
The cornied pad grew from the clearly visible base in
the lower part of the bony dome, and its upper end was
displaced dorso-aborally. The blood vessels located on
the bones surface contributed to the growth and partial
renewal of this formation. The dierent degrees of
roughness intensity on the surface of the dome indicates
that the keratoid cover was growing to a greater extent
for males, while this process was slower for females,
juvenile and old individuals.
A solid internasal septum indicates a signicant load
on the end of the muzzle. The presence of outgrowths
and roughness on the rostral parts of the nasal and
intermaxillary bones suggests a presence of a terminal
horn-like structure of cornied pad and a eshy upper
lip, which participated in the process of the soil hoeing
and selecting of food objects.
The signicant development of the atlas transverse
processes, the high spinous processes of other cervical
vertebrae, as well as the massive mastoid processes of the
temporal bone, the bifurcation of the occipital crest into
two lateral halves indicate a presence of powerful lateral
neck muscles that carry out lateral and dorsolateral head
movements in addition to the conventional dorsoventral
ones. The development of such a muscular system
conrms the adaptability of Elasmotherium to raking
the upper soil layer.
182 Vadim V. Titov et al.
ACKNOWLEDGEMENTS. The authors are grateful
to the sta of the V.I. Vernadsky State Geological
Museum (I.A. Starodubtseva), Institute of Zoology
of Ministry of Education and Science of Republic of
Kazakhstan (P.A. Tleuberdina), and Saratov Regional
Local History Museum (A.V. Biriukov) for the
opportunity to work with the material. We are thankful for
Dr. P.-O. Antoine and anonymous reviewer for the helpful
remarks and recommendations for the improvement of
the manuscript. The study was supported by the Russian
Science Foundation, project No. 16-17-10170-P.
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The nasal and frontal horns of two individuals of Ceratotherium simum were examined by x-ray computed tomography (CT scanning), gross observation of sectioned horn, and light microscopy of histological sections of the horn tissue. CT scans of both sets of horns reveal a periodic banding pattern that is evident upon gross observation of sections as darker bands of tissue. The overlap of these bands in both histological and CT slices suggests the presence of both a photoabsorbent component (melanin) and a radiodense component (calcium phosphate salts, most likely hydroxyapatite or octocalcium phosphate). The distribution of these two components in the horns is hypothesized to contribute to the differential wear patterns that produce the characteristic sweeping conical shape of rhinoceros horn from what otherwise (in the absence of wear and UV exposure) would be cylindrical blocks of constantly growing cornified papillary epidermis. Although extant rhinocerotids are unique in possessing a massive entirely keratinous horn that approximates the functions of keratin-and-bone horns such as those of bovid artiodactyls, the tissue structures that make up the horn are strikingly convergent with other examples of papillary cornified epidermis found in horses, artiodactyls, cetaceans, and birds.
Article
Although the modern Indian and Javan rhinos have a single horn on their noses, the extinct one-horned rhino Elasmotherium was a source for the legendary unicorn, because the latter had a very long horn on its forehead and lived with the prehistoric human beings who drew its images on cave paintings. Elasmothere rhinos first appeared in South Asia in the Early Miocene, but the origin of Elasmotherium has been unclear. All other elasmotheres have a weak or strong nasal horn, whereas Elasmotherium seems to lose the nasal horn of its ancestors and to get a huge frontal horn apparently abruptly. Here we report the first discovered skull of Sinotherium lagrelii from the Late Miocene red clays in the Linxia Basin, northwestern China. This skull has an enormous nasofrontal horn boss shifted posteriorly and a smaller frontal horn boss, which are connected to each other, indicating an intermediate stage for the single frontal horn of Elasmotherium. Morphological and phylogenetic analyses confirm that Sinotherium is a transitional taxon between Elasmotherium and other elasmotheres, positioned near the root of the giant unicorn clade and originated in a subarid steppe. The posteriorly shifted nasal horn has a more substantial support and the arched structure of the nasofrontal area is an adaptation for a huge horn.