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

wide and regularly curved. In its upper part there is
a wide deep groove, gradually becoming narrower
and shallower with the curving of the sympnysis.
Ramus ascendens wide and thick. All the area of
proc. angularis is thick at the base and strongly protruding
backwards. This thickness reaches as far as
proc. articularis. The anterior part of ramus ascendens
is significantly thinner, however, incl. proc. coronoideus
itself. All the ramus ascendens in this part is
laterally slightly concave. Foramen mandibulae wide
and deep. Proc. coronoideus almost vertical in the
anteriror part. Tips of the processes curved backwards;
at the posterior ends there is a moderate concavity
(incisure). Processus articularis thick and high.
Perpendicularly positioned, with well shaped articular
surfaces. Two rami of the mandible not parallel.
At the level of M 1 a widening begins, rami coming
closer again at the level of M 3 , then going apart again.
Most distant from each other at the posterior ends.
The incisors (tusks) are a sequence of the symphysis,
shaping the curve together with it. Their basis
starts deep inside the symphysis. There they are hollow,
their alveoli are of semi-circular shape (Fig. 8).
At the same time they are becoming thicker inside.
At the end of the symphysis the tusks are already
wholly solid. They gradually become thinner
and, curving in two directions – outwards and backwards,
go apart from each other. Their tips are pointed,
slightly smoothed only at the foremost part of the
inner side, but there is no clear flat surface. Their
tips end just below the end of processus angulare.
Lower cheek-teeth. (Pl. VI). The toothrows also have
five teeth each – two premolars and three molars.
Unlike the upper premolars, the lower are much
narrower, and their structure is very different,
especially P 3 .
P 3 has a long and narrow crown, pointed at the
anterior end. One large longitudinal ridge is situated
along its axis, and another, transversal – in the
posterior part. They form the occlusial surface of
the tooth. The longitudinal ridge is wider at its basis,
gradually narrowing towards the apex of the crown.
Its widest part is in the middle of the crown. There it
is more worn out and part of the dentine is seen. On
the inner part of the tooth, at the place where the
longitudinal ridge contacts the inner one, the first
narrows abruptly thus shaping a large triangular
valley. Outside the crown is smooth.
P 4 dext has a larger crown, elongated and wide.
The occlusal surface is moderately worn. It is formed
by two transversal ridges, contacting at the outer part
of the crown. At this place they divide the valley between
them in two not quite equal parts. The anterior
wall of the first ridge is strongly concave. The posterior
part of the crown has a weak cingulum.
M 1 dext has three transversal ridges. First two are
more worn. Their structure is generally the same as
in M 1 . All three ridges are wider on the outer side.
The valleys dividing them become gradually narrower
towards the outer part. In this part the anterior walls
of the second and third ridge are slightly convex but
26
Fig. 8. Shape of the tusks of Deinotherium thraceisensis sp. n.
A – shape of the tusks at the basis of the alveolus; B – shape of
the tusks at 115.0 mm from their basis in the symphysis; C –
cross-section of I dext at 600.0 mm from the symphysis –
natural size
they don’t touch the ridge in front of them. On the
inner side, at the bottom of each valley there is a weak
tubercle, and on the anterior side – a small cingulum.
Left M 1 resembles the right but is more worn.
M 2 dext is large and tetragonal. It has two thick
transversal ridges, wider on the outer side. There both
ridges form a small concavity. The valley between
them is deep and free but on the inner side there is a
small tubercle. On its anterior and posterior sides the
crown has a cingulum.
M 3 dext is large too but with an irregular tetragonal
shape. Built by two transversal ridges. The first is
wider. Both are widening outwards. At the ends –
inner and outer – they are slightly curved to the front,
forming with their anterior walls shallow valleys. The
valley between them is deep and unblocked. The
posterior talon on the inner side of the crown is formed
by numerous tubercles of different size.
Comparison. The structure of the described mandible
is close to the other species (Fig. 9).
The symphysis is moderately large. There are differences
in the shape of ramus horizontalis, proc.
articularis, proc. coronoideus and the tusks.
1. The symphysis of D. bavaricum H. v. Meyer is more
protruding. In D. levius Jourdan it is more rounded
and curved inwards and in D. giganteum Kaup, as
well as in D. gigantissimum Stefanescu and D. thraceiensis
sp. n. the curving is even stronger and more
gradual.