Deinotherium thraceiensis sp. nov. from the Miocene near Ezerovo ...

8. There are significant differences between the three
skulls in the occipital region. Os occipitale in D. thraceiensis
sp. n. is high, wide and at an angle of 80°
toward the forehead, and of ca. 70° to the plane of
the teeth. In D. giganteum Kaup these angles are 70°
and 50° correspondingly; in D. levius Jourdan the
declination of the occipital bone is even larger, so
the angle is only 60°. As a whole, the skull of D. levius
Jourdan is very flat and low. Os occipitale is visibly
concave and very wide, forming two lateral wings
(Fig. 6 C and D – OS). Those wings are almost lacking
in D. thraceiensis sp. n. and in D. giganteum
Kaup they are much less developed.
9. The position of the occipital condyles is rather
different (Figs. 5, 6, and 7 – oc). In D. thraceiensis
sp. n. they are situated in the middle and in the lower
part of the occipital bone, almost the same is their
position in D. giganteum Kaup, and in D. levius Jourdan
they are on the upper half of the noted bone.
According to Svistun, this permitted the animal to
raise its head almost at right angle to its neck, thus
fully using its back curved lower tusks.
10. Worth mentioning is a characteristic peculiarity
of the Gussiatin skull lacking in all the others,
including the skull from Ezerovo. This skull has a
double articulation with the mandible. Once by an
articular surface on the zygomatic process of the
temporal bone and then by a second surface on the
petromastoideum. Between those two surfaces is the
external meatus of the auditory canal. How and
when this second articular surface was used, is
unclear.
After comparing their anatomy we can see that
deinotheres could be divided in two groups. One includes
D. giganteum Kaup, D. gigantissimum Stefanescu,
D. thraceiensis sp. n., D. levius Jourdan and
D. indicus Falconer, which have larger teeth, and the
second – D. bavaricum H. v. Meyer, D. pentapotamiae
Lydekker and others, all with smaller teeth.
As a whole, the teeth are rather similar and differences
are seen mainly in the two premolars P 3 and P 4 .
In D. giganteum Kaup P 3 is more rounded on the
inner side. The two inner ridges are more perpendicular
to the outer one. The anterior inner ridge is not
connected with the outer and is at an acuter angle to it
than in other taxa. They almost don’t touch each other
on the inner side. If anything like that is observed in
these species, than it is down at the very basis. The
ridges merge when they are worn. The cingulum is
more clearly seen here. It consists of numerous large
and small tubercles on all sides of the crown.
No comparison with the third premolars of D. gigantissimum
Stefanescu is possible, because they have
been restored after D. giganteum Kaup.
In D. levius Jourdan the anterior inner ridge of P 3
is situated diagonally to the outer one and touches
it. The posterior one is wider and V-shaped in its
upper part, with a shorter anterior part. It is also diagonal
to the outer ridge, but does not touch it.
In D. indicum Falconer the inner ridges are some
more diagonally situated, compared to D. giganteum
Kaup, but their tips do not contact.
D. bavaricum H. v. Meyer has small P 3 s. Their
inner ridges are some more perpendicular to the outer
one. This is rather clear with the anterior inner ridge.
The valley between them is wider and deeper.
In D. pentapotamiae Lydekker, D. levius Jourdan
and D. indicum Falconer the differences are almost
the same, concerning the position of the two inner
ridges and the size of the tooth and its cingulum.
The fourth premolar of D. thraceiensis sp. n. has
inner ridges perpendicular to the outer one. The
posterior is narrower and longer. The triangular valley
surrounded by the posterior inner wall of the outer
ridge and the inner wall of the posterior ridge is
clearer than in all the other species.
D. gigantissimum Stefanescu has a longer P 4 . Its
transverse ridges are at a larger distance from each
other. Besides, it has a strong cingulum on the anterior
and the posterior side, lacking in our species.
In D. bavaricum H. v. Meyer P 4 s are smaller and
of a more regular square shape. The transverse ridges
are more distant at the inner side of the crown,
and the valley surrounded by them and the outer
ridge is wider and larger.
In D. levius Jourdan the posterior inner ridge is
also attached to the outer one with its longer posterior
branch.
In D. indicum Falconer and D. pentapotamiae
Lydekker the last premolars have a square shape and
are smaller. Their transverse ridges are parallel and
of equal size. The valley between them is larger and
everywhere equally wide.
In the M 1 s of D. giganteum Kaup, unlike D. thraceiensis
sp. n., the three ridges are almost of equal
size, with an equally developed cingulum on both
sides of the valleys, blocking them entirely on the
outer side. The latter is of significant taxonomical
value.
In D. gigantissimum Stefanescu has a developed
cingulum on the outer anterior and on the posterior
side of the crown, resembling a chain of large tubercles,
closely arranged along the end of the tooth.
There are no significant differences in the structure
of the first molars of D. bavaricum H. v. Meyer,
except in their size.
The other molars (M 2 and M 3 ) of D. thraceiensis
are not very different from those of the other species.
Mandible. (Pl. III, Fig. 1 and Pl. V).
Like the skull, it is entirely preserved. Compared to
the size of the body, it is not large (measurements in
Table 3). Ramus horizontalis long, high, wide and
laterally slightly flattened. Below P 3 there is a well
shaped double opening – foramen mentale. The
highest point of the mandible is at the symphysis, it
becomes lower towards the posterior end (see Plate
V). Because of this, the last molar is not horizontal,
but inclined backwards. Processus angularis is strongly
developed, and fossa masseterica is wide but not
very deep. The most typical feature of the animals
belonging to this group is the shape of the symphysis.
Together with the tusks, it is curved down and
back. In D. thraceiensis sp. n. the symphysis is solid,
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