Rhagapodemus cf. hautimagnensis Mein & Michaux, 1970

Popov, Vasil V., 2004, Pliocene small mammals (Mammalia, Lipotyphla, Chiroptera, Lagomorpha, Rodentia) from Muselievo (North Bulgaria), Geodiversitas 26 (3), pp. 403-491 : 453-456

Rhagapodemus cf. hautimagnensis Mein & Michaux, 1970 ( Figs 26 ; 27 A-H)

Rhagapodemus hautimagnensis Mein & Michaux, 1970: 2782 . — Van de Weerd 1979: 140, 141, pl. 2, figs 10-14.

MATERIAL EXAMINED. — 23 m 1 (Ms223-235), 1 mandibular fragment (Ms236), 10 m 2 (Ms235-241), 5 m 3 (Ms261-263), 18 M1 (Ms243-251, 264), 7 M2 (Ms252-258), 3 M3 (Ms242, 259, 260).

MEASUREMENTS. — See Table 9.

DESCRIPTION

m1: the anterocentral tubercle is fairly well developed and isolated on unworn teeth. In the latter stages of wear, it fuses with the anterior pair of cusps. In unworn teeth, the anterior and middle pairs of cusps are separated by a narrow valley. In some worn specimens, they are connected by a sagital pass. The posterior lamina is always isolated. The talonid is of medium size, oval and slightly elongated transversally. The labial accessory cusps are variable in size and number. The posterior one is always well developed, rounded and quickly becomes confluent with the hypoconid with wear. The other accessory cusps may lack, but more often, they are two, adjacent to the anterior and the middle pairs of cusps, respectively. In some specimens additional weak buds may occur.

m2: the accessory labial cusps, beside the anterior one, are poor (near the hypoconid) or lacking.

m3: there is a weak anterior add cusp.

M1: these molars possess three roots. The t1 is considerably pushed to the back and is separated from the t2. In some specimens t3 has a labially directed spur reaching the base of the t6. Most often, the t4 and t7 are not connected until the late stages of wear. Sometimes the t8 and t9 are also separated. The t7 is elongated and looks like a broad ridge. The posterior cingulum (t12) is well developed.

M2: the majority of teeth have three roots, but some specimens show 4 or 5 roots. The t1 is larger than the t3 and they are set apart. The pairs of adjacent cusps, t4/t7 and t8/t9, are separated during the early and middle wearing stages. The t7 is elongated.

M3: the tooth is three rooted. The t3 is lacking. The other cusps are connected in various combinations.

REMARKS

Some species of large murids, showing pronounced hypsodonty and presence of t7 on M1 and M2, are known from Europe. The first described species is Rhagapodemus frequens Kretzoi, 1959 , from the late Pliocene of Csarnóta (Carpathian basin, Hungary). This species is also recorded in Poland (Weze 1, Sulimski 1964). Subsequently, a more evolved form, Rh. frequens athensis De Bruijn & Van der Meulen, 1975 , was reported from the south of Greece (the early Pleistocene locality of Tourkobounia). This form is considered as a separate species by Martin Suarez & Mein (1998). Two closely related species differing in size were described from France: Rhagapodemus hautimagnensis Mein & Michaux, 1970 (large), and Rh. ballesoi Mein & Michaux, 1970 (small). The first species is also known from the early Ruscinian of Greece ( Van de Weerd 1979). Another species, Rh. wandeweerdi De Bruijn & Van der Meulen, 1975 , was reported from the isle of Rhodes (the locality Maritsa). Initially this material was described under the name Apodemus aff. jeanteti Michaux, 1967 ( De Bruijn et al. 1970). This short review of the Pliocene findings of the genus shows that it evolved in south and southeastern Europe. The main evolutionary trend is the increase of size and hypsodonty. The latest form, Rh. frequens athensis , is the largest one and has higher crowned molars. Therefore, it can be supposed that the forms of this phyletic lineage have stratigraphical significance for the Pliocene and the early Pleistocene.

The teeth from Muselievo are larger than these of the Greek population of Rhagapodemus hautimagnensis . In this respect, they are similar with Rh. hautimagnensis from its type locality ( Mein & Michaux 1970) as well as with Rh. wandeweerdi . On the other hand, the molars available are smaller than the molars of the latter forms ( Rh. frequens [ Sulimski 1964] and Rh. frequens athensis ). It appears that the Rhagapodemus -assemblage under consideration shows an intermediate evolutionary stage.

Although similar in size, the molars from Muselievo differs from Rhagapodemus wandeweerdi (cf. De Bruijn & Van der Meulen 1975) by: 1) having an oval posterior labial accessory cusp (c1) on m1, which fuses quickly with the hypoconid; 2) a poor or lacking posterior accessory cusp on m2; and 3) a large distance between the t1 and t3 on M2. In these features the material is similar with Rh. hautimagnensis and Rh. frequens . Therefore, if one considers these species as evolutionary stages of one phyletic lineage, the population from Muselievo provides a link between them. The material is tentatively referred to the first species on the basis of the similarity in size.

Although some small molars of Rhagapodemus are reminiscent at first glance of that of Sylvaemus they are readily distinguishable by their hypsodonty and occlusal pattern. In Rhagapodemus , the crowns of molars are high and the wear surfaces of the cusps and the ridges all lie in about the same (horizontal) plane. In contrast, in Sylvaemus , these surfaces are oblique to the horizontal plane and the ridges between cusps are lower ( Van de Weerd 1979).

Figures

FIG. 26. — Rhagapodemus cf. hautimagnensis Mein & Michaux, 1970, upper molars in occlusal view; A, right M1, Ms243; B, right M1, Ms244; C, right M1, Ms246; D, left M2, Ms253; E, right M2, Ms254; F, right M2, Ms255; G, right M3, Ms259; H, right M3, Ms260; I, right M3, Ms242. Scale bar: 1 mm.

FIG. 27. — A-H, Rhagapodemus cf. hautimagnensis Mein & Michaux, 1970, lower molars in occlusal view; A, right m1, Ms233; B, right m1, Ms234; C, right m1, Ms229; D, left m2, Ms237; E, right m2, Ms238; F, right m2, Ms235; G, left m3, Ms261; H, left m3, Ms262; I, J, Rhagapodemus sp., M1 in occlusal view; I, left, Ms302; J, right, Ms303. Scale bar: 1 mm.