Myomimus complicidentatus, Popov, 2004

Popov, Vasil V., 2004, Pliocene small mammals (Mammalia, Lipotyphla, Chiroptera, Lagomorpha, Rodentia) from Muselievo (North Bulgaria), Geodiversitas 26 (3), pp. 403-491 : 449-451

Myomimus complicidentatus n. sp. ( Fig. 25 A-I)

HOLOTYPE. — Right M2, Ms129 ( Fig. 25H ).

FIGURED PARATYPES. — 2 m 1 (ms122, 123), 3 m 2 (ms124, 125, 126), 1 m 1 (ms128), 2 m 2 (ms127, 129), 1 m 3 (ms130).

ETYMOLOGY. — Complicidentatus because of its complicated occlusal surface of the upper molars.

TYPE LOCALITY. — Muselievo, Bulgaria.

OTHER MATERIAL EXAMINED. — 1 m 2 (Ms125-1).

MEASUREMENTS. — See Table 8.

DIAGNOSIS. — A large Myomimus species with broad upper molars bearing centrolophs.

DIFFERENTIAL DIAGNOSIS. — Myomimus complicidentatus n. sp. has larger molars than Myomimus dehmi (De Bruijn, 1966) and Myomimus maritsensis De Bruijn, Dawson & Mein, 1970 . It differs from Myomimus qafzensis (Haas, 1973) and the Quaternary populations of M. roachi (Bate, 1937) in having broa- der upper molars, larger lower molars, and more complicated occlusal pattern of the upper molars, which always bear well developed centrolophs and some times an anterior extra ridge present.

DESCRIPTION

Lower molars (m1-2): the teeth show three roots. There are four main ridges on the concave occlusal surface – anterolophid, metalophid, mesolophid, and posterolophid. There is a posterior extra ridge in the valley between the mesolophid and posterolophid.

Upper molars (M1-2): three roots. The occlusal surface is clearly concave. In two specimens, the anteroloph is separated from the paracone as well as from the protocone. In one tooth (Ms127), it is connected with the protocone. The protoloph and metaloph meet and form a symmetrical arc. The posteroloph connects these ridges lingually. In most cases the anterior and posterior centrolophs are well developed, connected to the protoloph and metaloph, respectively. The anterior centroloph is usually larger.

M3: there are two centrolophs. The anterior one is longer, separated from the paracone.

REMARKS

The teeth from Muselievo are larger than those of the fossil species of the genera Myomimus , Peridyromys Stehlin & Schaub, 1951 , Microdyromys De Bruijn, 1966 and Ramys Garcia Moreno & Lopez Martinez, 1986 with similar dental pattern ( De Bruijn & Rumke 1974; Van de Weerd 1973; Storch 1975; Daams 1981; Hugueney 1968; Aguilar 1974): Myomimus maritsensis De Bruijn, Dawson & Mein, 1970 , M. dehmi (De Bruijn, 1966) , Myomimus sp. , M. roachi (Bate, 1937) , M. qafzensis (Haas, 1973) , Microdyromys koenigswaldi De Bruijn, 1966 , Peridyromys murinus (Pomel, 1953) , P. aquatilis (De Bruijn & Moltzer, 1974) and Ramys multicrestatus (De Bruijn, 1966) , (the taxonomy is after Daams & De Bruijn 1995). In size, the form from Muselievo is similar to the Miocene species Miodyromys aegercii (Baudelot, 1972) but it possesses a greater number of extra ridges ( Aguilar 1980).

In general, the teeth from Muselievo show rather complicated occlusal pattern, comparable with the earlier forms of the genus: Myomimus dehmi and M. maritsensis ( Daams 1981) . The dental pattern of the molars under study differs from that of Myomimus maritsensis by having somewhat more complicated occlusal surface: the constant presence of a posterior centroloph on M1-2 and posterior extra ridge on m1-2.

The occlusal pattern of the M1-2s available is more complicated in comparison with the Quaternary populations of Myomimus roachi ( Daams 1981; Van der Meulen & Doukas 2001). On the other hand, some specimens of the upper Pleistocene species Myomimus qafzensis ( Israel) also show a rather complicated occlusal surface: presence of centrolophs (M1-2). Nevertheless, the populations from Israel look more progressive (see below) since these ridges are shorter ( Daams 1981: pl. 3). An additional difference concerns the great frequency of the endoloph of M2s in the populations of Myomimus qafzensis (morphotypes C, Ce of M1-2, cf. Daams 1981). This ridge lacks in the small sample from Muselievo. As concern the lower molars, some middle and upper Pleistocene populations of M. roachi and M. qafzensis include specimens with posterior extra ridge. In these cases, again, the Pleistocene populations look more advanced in comparison with the material from Muselievo in having shorter extra ridges ( Daams 1981: pl. 2). Some of the available lower molars fall in the upper part of the size variability of these populations ( Daams 1981). The small size of the sample from Muselievo does not permit detailed comparisons, but the above-mentioned size differences do not allow to refer the material available to these species.

According to Daams (1981) the main trend within M. dehmi-M. roachi evolutionary lineage is towards a simplification of the dental pattern and size increase. The simplification includes the loss of the posterior extra ridge and the shortening of the centrolophid in the lower molars, while the M1-2s lose extra ridges and centrolophs. It is not clear whether the size differences between populations are due to spatio-temporal environmental variation or to evolution ( Daams 1981). The population from Muselievo fits well within this pattern. Having in mind the age of the locality (MN15b, see below), it can be supposed that the new species is a direct descendant of M. dehmi (MN9-12; Daams 1981). The northern position of the locality probably additionally strengthens the considerable size increase in comparison with the populations of M. dehmi from Spain and Greece ( Daams 1981). The earlier East Mediterranean species, M. maritsensis (MN14; Daams 1981), seems more progressive than the population from Muselievo in having a more simplified M1 occlusal pattern ( Daams 1981: fig. 30). Myomimus complicidentatus n. sp. can be considered as a potential ancestor of the upper Pleistocene M. qafzensis from Israel. The smaller size of the southern Pleistocene species can be attributed to a geographical variation.

Figures

FIG. 25. — A-I, Myomimus complicidentatus n. sp.; A, left m1, Ms122, occlusal view; B, right m1, Ms123, occlusal view; C, left m2, Ms125, occlusal view; D, right m2, Ms126, occlusal view; E, right m3, Ms124, occlusal view; F, left M1-2, Ms127, occlusal view; G, left M1-2, Ms128, occlusal view; H, right M2, Ms129, occlusal view (holotype); I, right M3, Ms130, occlusal view; J, K, Dryomimus eliomyoides Kretzoi, 1959; J, right M1-2, Ms132, occlusal view; K, left M1-2, Ms131, occlusal view; L-R, Glis minor Kowalski, 1956; L, right p4, Ms133, occlusal view; M, left M2, Ms134, occlusal view; N, right M2, Ms135, occlusal view; O, right P3, Ms136, occlusal view; P, right M1-2, Ms138, occlusal view; Q, right M1-2, Ms137, occlusal view; R, right M3, Ms139, occlusal view. Scale bar: 1 mm.