Neocricetodon cf. progressus

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 : 408-409

Neocricetodon cf. progressus

( TOPACHEVSKY et SCORIK, 1992) Pl. 9, Figs 7–13

M a t e r i a l. 4 m 1, 7 m2, 6 m3, 11 M1, 9 M2, 6 M3:

Volchaya Balka; 2 m 1, 1 M2: Gaverdovsky.

enclosing a shallow posterosinusid. A notch between the posterolophid and hypoconid is well expressed.

m3. The lingual anteroloph is small but well expressed, turning into a tiny ridge with wear. The short mesolophid reaches mid-depth of the mesosinusid. Te crescentic posteroloph connects to a stylid-like metaconid and closes a deep posterosinus.

M1. The anterocone cusps are separated by a shallow anterior depression and a deeper groove or a rounded basin of the anterosinus distally (Pl. 9, Figs 12–13). The well developed lingual anterolophule may be a single connection between the anterocon and the protocone-paracone region (n = 5), or may be accompanied by a much weaker labial anterolophule connecting to the labial spur of the anterolophule (anteromesoloph) (n = 3), or to the distal part of the lingual anterolophule (n = 1). An anteromesoloph is commonly present (n = 6), being long (n = 2), not reaching labial cingulum (n = 4), or absent (n = 1). The mesoloph extends for 2/3 of the mesosinus depth (n = 9) but does not reach the mesostyle. The posterior metaloph often closes a small posterosinus (n = 7). Most molars show a three rooted condition with a flattened but integer lingual root (n = 8). In one specimen the lingual roots are subdivided into two closely spaced roots.

M2. A well developed lingual anteroloph is a normal condition. A mesoloph is present in all specimens (n = 6). It

D e s c r i p t i o n. m1. Anteroconid cusps are closely spaced. The anterior surface is undivided and rounded (Pl. 9, Figs 7–9). Posteriorly anterocon cusps are weakly subdivided by a shallow groove. Anterolophulid is represented by its labial only (n = 2) or both branches (n = 3) delimiting a very small anterofossetid basin. The mesolophid is long and well developed (n = 4) or short not reaching mid-depth of the mesosinusid. A small bulge representing the mesostylid is present in most specimens. Ectomesolophid (n = 1) and ectostylid (n = 3) are occasionally present. The posterolophid connects to the very base of the entoconid leaving the sinusid open till latest wear stages. Two roots.

m2. The lingual anteroloph is very small, expressed as a shallow basin on the antero-lingual side of the metaconid, never becoming a ridge regardless of wear stages. The mesolophid is long (n = 6) but may be strongly obliterated in advanced wear stages (n = 2; Pl. 9, Fig. 10), or reaching middepth of the mesosinusid (n = 1). Long mesolophids usually connect with expanded mesostylid. The posterolophid usually connects to the posterior side of the entoconid may be long (n = 2), medium length and ending very shortly before the mesostylar margin (n = 5) as in M1, or short, reaching the mid-depth of mesosinus. A posterior metaloph is present in all specimens in the early or medium wear stages (n = 7) enclosing a small posterosinus. Four roots.

M3. A lingual anteroloph is present becoming a small ridge with moderate wear (Pl. 9, Fig. 13). A reduced mesoloph is present in most specimens as a laterally or anteriorly directed short bulge or ridge on the metaconal ridge. Three roots.

See Table 6 for measurements.

C o m m e n t s. Late Miocene faunas of south Eastern Europe show a transition from Neocricetodon dominated faunas in the late Vallesian and early Turolian to Pseudocricetus dominated faunas in the middle – late Turolian ( Topachevsky and Scorik 1992, Sinitsa 2012). This shift probably reflects a transformation from more closed to more open landscapes. The two synchronous faunas from the North Caucasus, alternatively dominated by one of the two genera, support a strict biotopic separation of these two lineages of hamsters. The morphological appearance of the Caucasian Neocricetodon represents a combination of characters of N. moldavicus (LUNGU, 1981) and N. progressus . With the former species recently revised by Sinitsa and Delinschi (2016) the described form shares a weak differentiation of anteroconid in m1, frequencies and manifestation degree of mesolophs, predominance of three-rooted M1. On the other hand, it resembles N. progressus in the comparable development of the anteromesoloph in M1 and mesolophs in upper molars, predominant development of a lingual anterolophule in M1, and the moderate development of lingual anterolophids in m2 – m3 and lingual anterolophs in the upper molars. It, however, appears more basal than both the type population from Novoelizavetovka 2 and the somewhat less derived form from Palievo ( Sinitsa 2012). From most Late Miocene central European species the described form differs by the less developed elements of dental complexity. Specifically, from the Vallesian Austrian species ( Daxner-Höck and Höck 2015) it differs in the relatively short m3 and M3 (from Kowalskia sp. A and B), in the three-rooted M1 (from Kowalskia sp. C ), and in double anteroconid (from Kowalskia sp. B and C). From the early Turolian N. falhbuschi (BACHMAYER et WILSON, 1970) it differs in smaller size, three-rooted M1, and relatively shorter m3/M3. From otherwise similar N. skofleki ( KORDOS, 1987) ( Daxner-Höck 1972, Kordos 1987, Freudenthal and Kordos 1989) it also differs in having a double-cusped anteroconid. We tentatively assign our form to N. cf. progressus .

Steklov (1966) studied the same sections near Maikop and found a single cricetine molar from the sandy beds with abundant shells of terrestrial snails dominated by Pomatias . We studied this molar (Steklov’s specimen 3044) in the collections of the Zoological Institute in Saint-Petersburg. The M1 (2.16 × 1.39) is identical in morphology (strong lingual anterolophule, long anteromesoloph, medium long mesoloph not reaching the mesostyle, posteroloph with defined posterosinus, three roots) to Neocricetodon from the Volchaya Balka sample.