Ochotonoma csarnotana ( Kretzoi, 1959 )

Popov, Vasil V., 2004, Pliocene small mammals (Mammalia, Lipotyphla, Chiroptera, Lagomorpha, Rodentia) from Muselievo (North Bulgaria), Geodiversitas 26 (3), pp. 403-491 : 437-438

Ochotonoma csarnotana ( Kretzoi, 1959) ( Fig. 19 )

Ochotonoides csarnotanus Kretzoi, 1959: 244 ; 1962: 312, abb. 6. — Terzea & Boroneant 1979: 179-181, fig. 4. — Bazarov et al. 1976: 63, pl. II, fig. 9. — Erbaeva 1988: 81, pl. 19, fig. 2. — Terzea 1997: 654, fig. 3.

Ochotonoma csarnotana – Sen 1998: 367.

MATERIAL EXAMINED. — 8 p3 (Ms59-67), 2 p3 (Ms380), 1 dp4 (Ms381, 19 lower cheek teeth (Ms382), 1 fragment of mandible with m1 (Ms76), 14 upper incisors (Ms383), 1 dP2 (Ms79), 1 P2 (Ms75), 3 dP2 (Ms384), 1 P2 (Ms385), 2 dP4 (Ms77-78), 8 dP4 (Ms386), 2 P4 or M1 (Ms71-72), 2 M2 (Ms73- 74), 7 M2 (Ms387), 20 upper cheek teeth (Ms388).

MEASUREMENTS. — See Table 7.

DESCRIPTION

P2 and dP2: an oblique and deep paraflexus separates the occlusal surface in two parts.

P3: the occlusal surface of the tooth is ellipsoidal, bearing a crescent shaped paraflexus, filled with crown cementum. The lingual margins of both hypocone and protocone are angular. The enamel is thin or lacking on the postero-buccal margin of the occlusal surface.

dP4: the occlusal surface is elongated. The inner part of the hypoflexus forms a kidney-shaped enamel islet.

The occlusal surface of P4 and M1 consists of two transverse lophs (anteroloph and posteroloph), separated by a deep hypoflexus, filled with crown cementum. Posteroloph and anteroloph are about equal in width.

M2: anteroloph is wider than posteroloph. There is a postero-lingual process.

p3: the outline of the occlusal surface is nearly triangular. It consists of two lophs, anterior (anteroconid) and posterior ones, which are separated by two deep reentrant folds, paraflexid and protoflexid. The two parts of the occlusal surface are linked by a narrow dentine isthmus. The paraflexid is directed obliquely backward, or, in one specimen, it is nearly parallel to the median axis of the occlusal surface. The protoflexid is transverse. In most specimens, the flexid’s margins are smooth. In two teeth, a slight irregular waviness can be observed. The shape of anteroconid is rhomboidal and its variability concerns the presence or absence of additional anterior reentrant folds. Two specimens (Ms59 and 67) possess two well developed anterior reentrant folds, filled with crown cementum. These teeth are similar to the materials known from Csarnóta-2 and Ciuperceni (see below). Other specimens have only buccal reentrant valley (Ms63, 64, 66) with variable depth. Three other teeth (Ms63, 64 and 66) show no traces of anteroflexid, or bear very shallow grooves without cementum. The posterior loph has a deep hypoflexid obliquely directed posteriorly. On two specimens, a trace of a mesoflexid occurs on the posterolingual margin. The enamel thickness is variable. It is thick in some parts of crown perimeter, while it is very thin or lacks in some others.

REMARKS

The available p3s differ from the members of the genus Pliolagomys Erbaeva, 1983 – P. kujalnikensis (Topacevski & Scorik, 1977) and P. danubicus (Topacevski & Scorik, 1977) –, described from the area of Odessa (the northern Black Sea coast), in having a more symmetrically situated anteroconid and smaller size. Moreover, the paraflexid of those species is nearly perpendicular to the sagital axis of the p3 occlusal surface. The oblique position of both paraflexid and protoflexid on the specimens from Muselievo corresponds to the morphology of Ochotonoides csarnotanus , known from Csarnóta-2 ( Erbaeva 1988) and Ciuperceni ( Terzea & Boroneant 1979). The available p3s are considerably smaller than those of the east Asiatic species of the genus Ochotonoides – O. primitivus Zheng & Li, 1982 and O. complicidens Boule & Teilhard de Chardin, 1928 . In addition, the material from Muselievo differs from the second species in having smooth margins of paraflexid and protoflexid. These differences clearly show that the west Palearctic members of this morphologic group should be distinguished as a separate genus. This was done by Sen (1998) who, based on the material from the Pliocene locality Çalta (MN15), Anatolia, Turkey, described the genus Ochotonoma . The type species of the new genus is O. anatolica Sen, 1998 , to which the material from Muselievo is very similar. The differences concern some details of the shape of p3: the more oblique paraflexid and the lack of a mesoflexid (only two specimens bear a trace of mesoflexid) in the sample from Muselievo. Additionally, the form from Muselievo seems slightly larger. In these respects, the material under study compares better with the few specimens from Hungary and Romania, originally referred to Ochotonoides csarotanus ( Kretzoi 1959, 1962; Terzea & Boroneant 1979). The variability of the form from Muselievo is great and includes specimens similar to both species. The co-occurrence of two species seems however unlikely, especially having in mind that the extreme morphotypes are connected by intermediate states. In this respect, the form from Muselievo can be considered as a link between the European and Anatolian forms, which corresponds to its intermediate geographical location. The distinction or identity between O. csarnotana and O. anatolica remains to be further substantiated based on further material from Csarnóta-2.

Figures

FIG. 19. — Ochotonoma csarnotana (Kretzoi, 1959), teeth in occlusal view; A, right p3, Ms59; B, left p3, Ms67; C, left p3, Ms61; D, right p3, Ms62; E, right p3, Ms63; F, right p3, Ms64; G, right p3, Ms65; H, left p3, Ms66; I, right p3, Ms60; J, right P3, Ms69; K, left P3, Ms70; L, left P2, Ms75; M, right dP2, Ms79; N, left P3, Ms68; O, left P4/M1, Ms72; P, right M2, Ms74; Q, right M2, Ms73; R, left dP4, Ms78; S, right m1, Ms76; T, right P4/M1, Ms71; U, left dP4, Ms77. Scale bar: 1 mm.