Trischizolagus dumitrescue Radulesco & Samson, 1967

Popov, Vasil V., 2004, Pliocene small mammals (Mammalia, Lipotyphla, Chiroptera, Lagomorpha, Rodentia) from Muselievo (North Bulgaria), Geodiversitas 26 (3), pp. 403-491 : 443-445

Trischizolagus dumitrescue Radulesco & Samson, 1967 ( Fig. 23 )

Trischizolagus dumitrescue Radulesco & Samson, 1967: 544-563 . — Terzea 1997: 656, fig. 4D-F.

Alilepus sp. – Daxner & Fejfar 1967: 43-46, taf. I, figs 1-4; abb. 5a-e.

Pratilepus kutschurganicus Topachevsky, 1980: 38 , 39, figs 1-17.

MATERIAL EXAMINED. — 6 p3 (Ms80-85). MEASUREMENTS. — p3 (L × W) = 3.3 × 3.5; 3.12 × 3.2; 3.57 × 3.00; 3.42 × 3.45; 2.6 × 2.95.

DESCRIPTION

Both hypoflexid and metaflexid are well developed, reaching near the sagital axis of the occlusal surface, and as a result the dentine bridge between the anterior and posterior segments of the occlusal surface is narrow, or absent (one specimen: Ms82). In one tooth only (Ms85) the metaflexid is relatively shallow. In some teeth, the posterior wall of these reentrant folds is slightly wavy. The paraflexid and protoflexid are well pronounced. The anteroflexid is clearly visible on most teeth as a broad and shallow reentrant valley with slightly folded margins in some specimens.

REMARKS

The p3s under consideration show greatest resemblance with Trischizolagus dumitrescuae and Pratilepus kutschurganicus Topachevsky, 1980 (waviness of the posterior wall of the hypoflexid and metaflexid). According to Topachevsky (1980), these species are very similar and the main difference concerns the presence of reentrant folds on the anterior wall of P2. However, it is debatable whether it is justified to lump certain types of upper premolars with groups of lower premolars having in mind the great diversity of leporids during this time. This author did not provide any clear argumentation in this respect. Some P2s with poorly developed lateral reentrant valleys, similar to those of Trischizolagus , have been referred to another species described from the locality, Pratilepus ucrainicus Topachevsky, 1980 . Moreover, as in Muselievo, the presence of representatives of the genus Pliopentalagus , for instance P. moldaviensis Gureev & Konkova, 1964 is also possible. Based on these considerations, for the time being, I regard Pratilepus kutschurganicus as a junior synonym of Trischizolagus dumitrescuae . The same opinion has been recently presented by Averinov & Tesakov (1997) regarding the leporids from Novopetrovka and Kuchurgan ( Pratilepus kutchurganicus , P. ukrainicus , and Seregnetilagus orientieuropaeus Topachevsky, 1987) as Trischizolagus cf. dumitrescuae . The teeth from Malusteni, reported under the name Alilepus sp. ( Daxner & Fejfar 1967) without doubt also belong to T. dumitrescue , described from the same locality ( Radulesco & Samson 1967). One tooth from Muselievo (Ms85) shows similarity with Trischizolagus maritsae De Bruijn, Dawson & Mein, 1970 in having a relatively broad connection between anterior and posterior parts of the occlusal surface. According to De Bruijn et al. (1970), this is a primitive feature. Since this peculiar pattern is presented only in one tooth in the studied material, it can be supposed that the form from Muselievo is more advanced than T. maritsae . The same suggestion derives from the comparisons of the measurements of p3. According to Averianov & Tesakov (1997), this tooth shows a gradual increase in size from the early to the late Ruscinian. The p3s from Muselievo are larger than those from Maritsa (MN14) and cover the range of the sample of T. dumitrescuae from Malusteni and Beresti (MN15) ( Radulesco & Samson 1967). Based on the broad overlap of the samples of different age, Averianov & Tesakov (1997) consider all the material they studied, including T. maritsae , belong to a single species, T. dumitrescuae . The above comparisons allow concluding that the p3 sample from Muselievo is very similar to T. dumitrescuae from the late Ruscinian (MN15) localities from Romania and Moldavia ( Radulesco & Samson 1967; Daxner & Fejfar 1967; Averianov & Tesakov 1997). The difference concerns the constant occurrence of very deep para- and protoflexids on the trigonid of p3s from Muselievo. Based on the drawings presented by Averianov & Tesakov (1997) it seems that these reentrants are more frequent within the MN15 samples, although they are not so deep as in the studied material. In this respect, the available p3s show similarity with the recent Pronolagus crassicaudatus (Geoffroy, 1832) from East Africa and seem more derived than T. dumitrescuae from the type locality. For the time being, having in mind the limited available sample and the possible ontogenetic variation of the deepness of the para- and protoflexids ( Averianov & Tesakov 1997), I consider these differences not enough for the species distinction of the form from Muselievo.

Figures

FIG. 23. — Trischizolagus dumitrescue Radulesco & Samson, 1967, p3 in occlusal view; A, right, Ms85; B, right, Ms81; C, left, Ms82; D, left, Ms80; E, right, Ms83; F, right, Ms84. Scale bar: 1 mm.