Pliocene small mammals (Mammalia, Lipotyphla, Chiroptera, Lagomorpha, Rodentia) from Muselievo (North Bulgaria)
Author
Popov, Vasil V.
Institute of Zoology, Bulgarian Academy of Sciences, Boul. Tsar Osvoboditel 1, 1000 Sofia (Republic of Bulgaria) popov @ zoology. bas. bg
text
Geodiversitas
2004
26
3
403
491
journal article
10.5281/zenodo.5377199
1638-9395
5377199
Dolomys occitanus
(
Thaler, 1955
)
(
Figs 33-35
)
Mimomys occitanus
Thaler, 1955: 1255-1257
. —
Chaline 1974: 343-353
, figs 3-8, 9 5,6. —
Terzea 1981: 119-124
, figs 2, 3, 4A-D, 5A, B. —
Chaline
et al.
1981: 821-826
.
Mimomys hassiacus atavus
Fejfar, 1961b: 57-60
, taf. 18, figs 5, 6; abb. 5a, c, 6d.
Mimomys stehlini
–
Chaline & Michaux 1975: 749- 757
, pl. I, text-fig. 1.
Dolomys odessanus
–
Topachevsky & Nesin 1989: 49
, fig. 18.
FIG. 32. —
Propliomys
cf.
hungaricus
Kormos,1934
, first lower molars;
A
, right, Ms43, occlusal view;
B
, left fragment, Ms47, occlusal view;
C
, left fragment, Ms45, occlusal view;
D
, left fragment, Ms46, occlusal view;
E
, left fragment, Ms48, occlusal view;
F
, right, Ms44, occlusal view;
G
, right, Ms43, buccal view;
H
, right, Ms44, buccal view;
I
, left, Ms46, buccal view;
J
, left, Ms47, buccal view;
K
, left, Ms45, buccal view;
L
, left, Ms48, buccal view. Scale bar: 1 mm.
FIG. 33. —
Dolomys occitanus
(
Thaler, 1955
)
, first lower molars in occlusal view;
A
, right, Ms42;
B
, left, Ms1;
C
, left, Ms2;
D
, right, Ms3;
E
, right fragment, Ms5;
F
, left fragment, Ms6;
G
, right fragment, Ms4;
H
, right fragment, Ms7;
I
, left, Ms8;
J
, right, Ms9;
K
, right, Ms10;
L
, right, Ms11;
M
, left, Ms12;
N
, right, Ms13;
O
, left, Ms14. Scale bar: 1 mm.
Promimomys konstantinovae
–
Topachevsky & Nesin 1989: 82-86
, fig. 31.
Dolomys occitanus
–
Maul 1996: 348
. — Fejfar & Reppening 1998: 163, abb. 3, 5. —
Dahlmann 2001: 73
, abb. 20: 37-52
MATERIAL EXAMINED
. —
23 m
1: morphotype “
Mimomys
”:
17 m
1 (9 fragments, 8 intact [Ms7-14]; morphotype “
Dolomys
”:
6 m
1 [Ms1-6, 42], 19 M3 [Ms23-40])
.
MEASUREMENTS (Min-M-Max, SD, N). — Lm1 = 2.67-2.91-3.20, 0.169, 8; am1 = 1.00-1.26-1.37, 0.163, 7; Wm1 = 1.07-1.23-1.65, 0.191, 8; LM3 = 1.50-1.76-2.00, 0.127, 17.
DESCRIPTION
There is no crown-cementum in the side folds of the molars. In most specimens, the enamel is not differentiated, but in some teeth it is slightly thinner on the tips of the salient angles. The crown is moderately high but the dentine tracks of the
linaea sinuosa
are low.
m1: the variable shape of occlusal surface can be classified into two morphotypes, called “
Dolomys
”- and “
Mimomys
”-morphotypes. The “
Dolomys
”-morphotype (
Fig. 33
A-G) is characterized by an open isle fold. The Sb3-wall is in a low position. The “
Mimomys
”-morphotype bears
Mimomys
-ridge, prism-fold and isle-fold or enamel islet (
Fig. 33
H-O).
M3: in unworn or slightly worn specimens, the BRA1 and LSA3 are deep, but after some wear they become reduced by insulation. The anterior islet vanishes quickly with further wear, while the posterior one is a long persistent structure, presented even in some worn teeth (Ms40). The clear relationship between the stage of wear and the number of islets indicates that all teeth belong to one species. Most teeth bear two roots. The anterior root is a compound structure, formed by the fusion of two roots. In some specimens the anterior fangs, although partially fused, are still clearly visible (Ms23, 25, 26, 35, 37-39). One tooth shows a very small third root (Ms23).
REMARKS
There is a great controversy regarding the taxonomic status of the “
Dolomys
” and “
Mimomys
” morphotypes of m1s referred to this species.
Sulimski (1964)
described them as two separate species –
Dolomys
cf.
hungaricus
and
Mimomys
cf.
stehlini
Kormos, 1931
.
Chaline (1974)
found in the large assemblage from Sète that these
types
are connected by intermediate forms, depending mainly on the stage of wear (see also
Van
de Weerd 1979
: table 9), and he therefore regarded the whole material as one highly variable species,
Mimomys occitanus
. It is a primitive, more or less mesodont form with a relatively high share of specimens in which the isle-fold remains open even in the advanced stages of crown wear – the so called “
Dolomys
”-morphotype. According to
Chaline (1974)
and
Chaline & Michaux (1975)
two evolutionary lineages derived from this variable species: one leading through
Mimomis
stehlini
Kormos, 1931
,
M. polonicus
Kowalski, 1960
,
M. pliocaenicus
(Forsyth Major, 1889)
, and
M. savini
Hinton, 1910
to
Arvicola mosbachensis
(Schmidtgen, 1911)
, the other one through
Propliomys hungaricus
and
Pliomys episcopalis
Méhely, 1914
to
P. lenki
(Heller, 1930)
[=
P. coronensis
(
Méhely, 1914
)
]. The former phyletic sequence is referred to the “
Mimomys
”-lineage, the later one to the “
Dolomys
”-lineage. In fact, the second lineage represents the evolution of
Propliomys
-
Pliomys
Méhely, 1914
(
Kretzoi 1955
,
1962
;
De Bruijn &
Van
der Meulen 1975
; Chaline 1975). This disagreement in the nomenclature within the second lineage reflects the similarity in teeth morphology of the earliest forms of these related genera (
Dolomys
and
Propliomys-Pliomys
) (
Nehring 1898
;
Méhely 1914
;
Hinton 1926
;
Kormos 1934b
). On the other hand the co-occurrence of the “ancestral” (“
Dolomys
”-morphotype of
M. occitanus
) and the derived forms (typical
Propliomys
with relatively high enamel free areas on m1) in Muselievo does not confirm that they belong to the same phyletic lineage. The lineage
Propliomys-
Pliomys
apparently constitutes an early specialized branch of the evolution of voles and cannot be regarded to derive from
Mimomys occitanus
as though by
Chaline & Michaux (1975)
.
According to
Van
de Weerd (1979)
,
M. occitanus
is an intermediate stage of evolution from
Promimomys
Kretzoi, 1955
to the advanced forms of
Mimomys
Forsyth Major, 1902
. During this evolution, morphological changes of m1 with a variable direction have been proposed: from forms with an isolated islet (
Promimomys
and
Mimomys davakosi
Van de Weerd, 1979
) through an open islet (most specimens in
M. occitanus
) to an isolated islet again (
M. stehlini
) (
Van
de Weerd 1979
). This variable trend however seems unlikely, having in mind that the direction of an evolutionary change is usually irreversible.
FIG. 34. —
Dolomys occitanus
(
Thaler, 1955
)
, first lower molars in buccal view;
A
, right, Ms42;
B
, left fragment, Ms1;
C
, right fragment, Ms7;
D
, left fragment, Ms2;
E
, left fragment, Ms8;
F
, right fragment, Ms11;
G
, right fragment, Ms13. Scale bar: 1 mm.
The analysis of the detailed morphology of the enamel islet in the anteroconid of the m1 of
Dolomys
,
Promimomys
and
Mimomys
presented by
Maul (1996)
provides a new perspective for the solution of this evolutionary and taxonomic problem.
Maul (1996)
found that
M. occitanus
differs from the earliest members of the genera
Promimomys
and
Mimomys
in having a low positioned wall of the
Mimomys
-isle (Sb3-wall). This feature is considered a derived one, leading to an evolutionary trend toward lowering of the wall. With the decrease in the height of the wall more
Dolomys
-morphotypes appear in a population which have greater functional advantage because of their longer cutting edges. In this context, it seems likely that
M. occitanus
is an ancestral species to forms with a lower Sb3-wall like
Dolomys nehringi
and does not belong to the
Promimomys-Mimomys
evolutionary lineage comprising voles with a higher Sb3-wall (
Maul 1996
). For the time being, this hypothesis is the best solution of the problem and the attribution of the species “
occitanus
” to the genus
Dolomys
is followed here. According to
Fejfar (2001)
, in contrast to the previous views (
Chaline 1974
;
Chaline & Michaux 1975
;
Van
de Weerd 1979
), the evolutionary chain leading to
M. stehlini
is as follows:
M. davakosi
Van de Weerd, 1979
-
M. gracilis
(
Kretzoi, 1959
)
-
M. stehlini
.
According to the structure of M3, the genus
Dolomys
is rather specific and comprises such large species as
D. milleri
Nehring, 1898
and
D. nehringi
Kretzoi, 1959
(Chaline 1975)
. The occlusal pattern of m1 of these species (see for example
Kretzoi 1962
: abb. 4;
Rabeder 1981
: abb. 182) is quite different from the “
Dolomys
”- morphotypes of
Dolomys occitanus
. In this context the opinion of
Maul (1996)
that
D. occitanus
is an ancestor of
D. nehringi
seems unlikely. The occurrence of M
3 in
the locality very similar to
D. nehringi
confirms this opinion.
The same line of reasoning can be developed against the Chaline’s hypothesis that
Dolomys
- morphotypes of
D. occitanus
represent an ancestral form for
Propliomys hungaricus
. The “
Dolomys
”-morphotype is quite different from the m1s of the true
Propliomys hungaricus
from Csarnóta-1 (
Kormos 1934b
: fig. 46;
Terzea 1981
: fig. 5s, d) and their co-occurrence in Muselievo (see above) indicates that this genus cannot be considered as a derivate of
D. occitanus
. For the time being, it can be said only that the ondatrine taxa, occurring in the European Pliocene [
Dolomys occitanus
(
Thaler, 1955
)
,
Dolomys milleri
(
Nehring, 1898
)
,
Dolomys nehringi
Kretzoi, 1962
,
Dolomys adroveri
(
Fejfar, Mein & Moissenet, 1990
)
, and
Propliomys hungaricus
(Kormos, 1934)
], represent a mosaic of species related to
D. occitanus
, which radiated quickly during the Ruscinian and early Villanyian (MN14-16-zones) (
Fejfar & Repenning 1998
).
As a whole, the population from Muselievo corresponds to the variability of
Dolomys occitanus
from the
type
locality (Grotte 1 de Sète) (
Chaline 1974
). In the scatter diagram composed for Lm1 and Em1 (
Chaline 1974
: fig. 2) the specimens from Muselievo would occupy the upper half of the cluster of the population from Sète. Hence, the material under study represents a slightly more advanced form. The m1s from Muselievo resemble also
D. occitanus
from Ciuperceni-
2 in
both size and morphology (
Terzea 1981
,
1997
; and pers. comm.) and differ only in having somewhat higher dentine tracks. Most probably the material from the nearby Romanian locality Dranic, determined as
Mimomys moldavicus
(Radulescu & Samson 1996)
belongs to
D. occitanus
too, having in mind that
M
.
moldavicus
(Kormos, 1932)
is a rather primitive form with extremely low dentine tracks, referable to
Promimomys
(Fejfar
et al
. 1990)
.
In general, the material from Muselievo is very similar to m1 and M3 sample of
Dolomys occitanus
from Wölfersheim (
Germany
) (
Fejfar & Repenning 1998
;
Dahlmann 2001
). The difference concerns only the somewhat longer m1 and the hyposinusids slightly lower in the sample from Muselievo.
FIG. 35. —
Dolomys occitanus
(
Thaler, 1955
)
, third upper molars;
A
, left, Ms23, occlusal view;
B
, right, Ms24, occlusal view;
C
, right, Ms25, occlusal view;
D
, right, Ms26, occlusal view;
E
, left, Ms27, occlusal view;
F
, right, Ms28, occlusal view;
G
, left, Ms29, occlusal view;
H
, left, Ms30, occlusal view;
I
, right, Ms31, occlusal view;
J
, left, Ms32, occlusal view;
K
, right, Ms33, occlusal view;
L
, left, Ms34, occlusal view;
M
, right, Ms35, occlusal view;
N
, left, Ms36, occlusal view;
O
, left, Ms37, occlusal view;
P
, left, Ms38, occlusal view;
Q
, left, Ms39, occlusal view;
R
, right, Ms40, occlusal view;
S
, left, Ms23, lingual view;
T
, the same, buccal view;
U
, right, Ms24, lingual view;
V
, the same buccal view. Scale bar: 1 mm.
The “
Mimomys
” morphotypes of
D. occitanus
are superficially similar to
M. davakosi
but differ in having higher dentine tracks (
Van
de Weerd 1979
). This difference is clearly visible in relation to the material from Ptolemais 3, the
type
locality of
M. davakosi
, especially in respect to the anterosinuid. Moreover,
M. davakosi
, being a typical member of the
Mimomys
lineage, shows a higher position of the Sb3-wall (cf.
Maul 1996
: fig. 3).