Allocricetus bursae Schaub, 1930

Popov, Vasil V., 2004, Pliocene small mammals (Mammalia, Lipotyphla, Chiroptera, Lagomorpha, Rodentia) from Muselievo (North Bulgaria), Geodiversitas 26 (3), pp. 403-491 : 460

Allocricetus bursae Schaub, 1930 ( Fig. 24 D-G)

Allocricetus bursae Schaub, 1930: 33 .

MATERIAL EXAMINED. — 2 M1 (Ms311, 313), 2 m 1 (Ms309-310).

MEASUREMENTS (L × W). — M1 = 1.82 × 1. 30; 1.95 × 1.29; m1 = 2.00 × 1.22; 1.97 × 1.27.

DESCRIPTION

m1: the anteroconid consists of two poorly individualized cusps, which are either in close connection (unworn specimen) or widely associated but with separated dentine fields (slightly worn specimen). Although there is a short spur on the anterolophid, directed postero-labially, the anterosinusid remains open. The anterolophulid is single. The main tubercles alternate. The mesolophid is lacking. The posterolophid is well developed but it does not close the posterosinusid.

M1: the anterocone is bicuspide but its parts are closely situated, so, in some cases, their anterior parts connect and form an anterior pit. The main cusps are opposite and the inner parts of the respective labial valleys soon become reduced by the conversion of their inner portions into enamel pits. The posterior cingulum is well developed.

REMARKS

The early evolutionary stages of small hamsters of modern type, such as Allocricetus , Cricetulus Milne-Edwards, 1867 , Tscherkia Ognev, 1914, and Cricetinus Zdansky, 1928 are poorly known. Four forms, Cricetulus sp. I , Cricetulus sp. II, Cricetinus europaeus Kretzoi, 1959 and Cricetinus beremendensis Hir, 1994 , similar in size to the material from Muselievo, are known from some Vallesian (Sumeg, MN10) and Pliocene (Osztramos 1, Csarnóta, Beremend 15, MN14- 16) localities of Hungary ( Kordos 1987; Hir 1994). These forms differ from the population under study in having an undivided anteroconid on m1. This feature may be considered as a primitive one. More over Cricetinus europaeus from Csarnóta-2 shows a double anterolophulid on this tooth. On the other hand, the occlusal pattern of M1 of C. europaeus is very similar to the material from Muselievo and to the Pleistocene populations of Allocricetus bursae . The Far East Pleistocene species Cricetinus varians Zdansky ( Fejfar 1970; Vorontsov 1982) differs from the Hungarian species by having mesolophid on the lower molars.

The material from the late Pliocene locality Maritsa (the isle of Rhodes, Greece), described as? Cricetulus sp. ( De Bruijn et al. 1970) is similar in size with the specimens from Muselievo but it differs in the presence of a short mesolophid on m1. According to Sen (1977), these specimens should be referred to Mesocricetus primitivus De Bruijn, Dawson & Mein, 1970 , described from the same locality.

The teeth from the Slovakian locality Ivanovce (MN15), described as Allocricetus cf. bursae , are smaller than the specimens from Muselievo. In this respect, they differ also from the comparative material of A. bursae from Zirany and Hundsheim ( Fejfar 1970). Moreover nearly all M1s from Ivanovce show undivided anterocone, while this tubercle is clearly divided in the material from Muselievo.

The available teeth are similar in size and overall occlusal pattern to the Pleistocene populations of Allocricetus bursae from Bulgaria. Although the anteroconid of the m1s from Muselievo is clearly divided, both parts are closely set, giving in this way a more primitive appearance of the population under consideration. However, this feature occurs also in some Pleistocene samples of Allocricetus bursae from Bulgaria (Varbeshnitsa, Morovitsa) ( Popov 1988, 1989). These comparisons suggest that the teeth from Muselievo most probably belong to a primitive form of Allocricetus bursae .

Figures

FIG. 24. — A, Pliopetaurista dehneli (Sulimski, 1964), left p4, Ms141, occlusal view; B, Sciurus sp., left M1-2, Ms142, occlusal view; C,?Spermophilus sp., right p4, Ms143, occlusal view; D-G, Allocricetus bursae Schaub, 1930; D, right m1, Ms309, occlusal view; E, right m1, Ms310, occlusal view; F, left M1, Ms313, occlusal view; G, left M1, Ms311, occlusal view; H, Tamias orlovi (Sulimski, 1964), left M3, Ms144, occlusal view. Scale bars: 1 mm.