Pseudocricetus TOPACHEVSKY et SCORIK, 1992

Tesakov, Alexey S., Titov, Vadim V., Simakova, Alexandra N., Frolov, Pavel D., Syromyatnikova, Elena V., Kurshakov, Sergey V., Volkova, Natalia V., Trikhunkov, Yaroslav I., Sotnikova, Marina V., Kruskop, Sergey V., Zelenkov, Nikita V., Tesakova, Ekaterina M. & Palatov, Dmitry M., 2017, Late Miocene (Early Turolian) Vertebrate Faunas And Associated Biotic Record Of The Northern Caucasus: Geology, Taxonomy, Palaeoenvironment, Biochronology, Fossil Imprint 73 (3 - 4), pp. 383-444 : 407

Genus Pseudocricetus TOPACHEVSKY et SCORIK, 1992

Pseudocricetus cf. antiquus TOPACHEVSKY et SCORIK, 1992 Pl. 9, Figs 1–6

M a t e r i a l. 5 m 1, 9 m2, 4 m3, 3 M1, 7 M2, 5 M3:

Gaverdovsky.

D e s c r i p t i o n. A smaller hamster ( Tab. 5) with a typical cricetine dental pattern with strongly reduced short sloping ridge (Pl. 9, Fig. 3). The posterosinusid forms a fossetid after moderate wear. Two roots.

M1. The anterocon is significantly divided. Equally developed lingual and labial anterolophules connect the anterocon with protocon-paracone region and delimit a small anterocon fossette. Deep anterior and posterior basins are delimited by high proto- and metalophs. Mesolophs are not present. Posteroloph connects to metacone posteriorly, posterior metalophule is not present (n = 3). Two of three available molars show four roots with distinctly separated lingual roots.

M2. The anteroloph is well developed, its lingual branch delimits a moderately developed protosinus. As in M1, high additional elements. Lower and upper incisors are oval in transverse section with a marked smoothed ledge on the anterior surface. The enamel does not extend to the medial side of the incisors.

m1. Cusps of the anteroconid are well defined and separated by anterior and posterior valleys (n = 3). An anterostylid is present in one specimen (Pl. 9, Fig. 1). The anteroconid connects to the protocone-metacone pair by an anterolophulid with its two almost completely fused branches enclosing a small anterofossetid. Mesolophid is strongly reduced and expressed as a short sloping ridge reaching at maximum the mid-depth of mesosinusid. Two roots.

m2. Labial anterolophid is well developed, running to the base of protoconid but never closing the protosinusid. The lingual anterolophid is weakly developed, not forming an enamel-dentine ridge with wear, and in most cases appearing as a shallow basin on the anterointernal side of the metaconid. Mesolophids are absent (n = 4), or present only as a short swelling (n = 4) sometimes with a sloping ridge nearly reaching mid-depth of the mesosinusid. A weakly developed ectomesolophid (n = 1) and ectostylid (n = 2) may be present (Pl. 9, Fig. 2). A distinct posterior notch between hypoconid and posteroloph is present in all specimens. The posterosinusid remains open regardless of wear. Two roots. The posterior root is strongly built, wide and flattened with a concave anterior face. The anterior root is much thinner, with an oval cross-section.

m3. Anterolophid expression as in m2, the lingual branch is present but weakly developed, never forming a lophid with wear. The mesolophid is strongly reduced but always expressed as a distinct bulge on the ectolophid or even a proto- and metalophs close anterior and posterior basins with early wear. Posterior metalophule is present in two specimens. Four roots.

M3. The labial anteroloph is strong and forms a ridge after wear. The lingual anteroloph is weakly expressed. Two fossae are formed after slight wear, similar to M1–2. The mesoloph is usually significantly reduced. It is present (n = 4) as a short, anteriorly directed bulge on the anterior metalophule or as a long ridge reaching the paracone (n = 1). The posterior basin may be crossed by a tiny posterior metalophule (n = 1; Pl. 9, Fig. 6). Three roots.

C o m m e n t s. The middle and late Turolian cricetines with a simple dental pattern in Eastern Europe are traditionally attributed to the genus Pseudocricetus TOPACHEVSKY et SCORIK, 1992 . The sequence of P. antiquus - P. orienteuropaeus (MN 12)- P. kormosi (MN 13) was shown to manifest a reduction of mesolophs/mesolophids and size increase. The early Turolian faunas from the northern Black Sea region mostly contain abundant Neocricetodon and rare Stylocricetus ( Topachevsky and Scorik 1992, Nesin 2013). In all hitherto known faunas in the region the cricetines form monodominant assemblages with either Pseudocricetus or Neocricetodon . Sinitsa (2010) showed that presumably chronoclinal characters, such as a degree of mesoloph/mesolophid reduction, may be variable and mosaic in different samples of Pseudocricetus from early and middle Turolian. If related to Pseudocricetus , the early Turolian cricetine from North Caucasus may represent one of its geologically oldest populations or belong to a basal radiation of this group of hamsters. The small sample size hampers the clear understanding of the variability in the Caucasian form. On the other hand, its comparison with early – middle Turolian forms from Ukraine shows obviously basal characters in the Caucasian form. These include well expressed mesolophids in m 1 in half of the specimens (Pl. 9, Fig. 1), occasional ectomesolophid in m2 (Pl. 9, Fig. 2) and, in a reduced form, in m1, weakly expressed lingual branches of the anterolophid in m2 – m3, and labial branches of anteroloph in M2 – M3, occasional presence of a posterior ridge of the metacon (posterior metalophule) in M1 – M2. The length of lower m3 equals or exceeds that of m2, which is typical for Pseudocricetus . Apparent increased hypsodonty of some ontogenetically younger molars, especially upper ones, may represent a regional specific feature. More material is needed to refine the taxonomic placement of the described sample of P. cf. antiquus .