Microstonyx major (Gervais, 1848)

Geraads, Denis, Spassov, Nikolaï, Hristova, Latinka, Markov, Georgi N. & Tzankov, Tzanko, 2011, Upper Miocene mammals from Strumyani, South-Western Bulgaria, Geodiversitas 33 (3), pp. 451-484 : 468

Microstonyx major (Gervais, 1848)

From Str-2, the material includes a maxilla with both complete cheek-tooth rows FM-2801 ( Fig. 3I ) and two subadult mandibles FM-2327 and FM- 2802, with missing rami (measurements are given in Table 3). The only find from Str-1 is a large i1. There was no p1 on either mandible. The cheekteeth are close in their dimensions to the Kalimantsi ones ( Kostopoulos et al. 2001). The same is true of the maxillary teeth that reach or slightly exceed the maximum size of the Kalimantsi population. The apex of the P4 protocone (FM-2801) is positioned midway between the tips of the labial cones. The part of the maxilla anterior to P2 is not preserved and the presence/absence of P1 is unclear, but if present, it was not in close contact with P2.

The evolutionary trends, the significance of tooth size and the taxonomy of Microstonyx Pilgrim, 1926 aredebated. Like former authors ( Made et al. 1992; Kostopoulos 1994; Made 1997; Kostopoulos et al. 2001; Liu et al. 2004) we failed to find any significant morphological difference between the various populations, but metric differences have been variously interpreted. Kostopoulos (1994) and Bonis & Bouvrain (1996) hypothesized that the early Turolian M. erymanthius (Roth & Wagner, 1854) (or the subspecies M. major erymanthius ) can be distinguished from the middle/late Turolian M. major (or M. major major ); Sylvestrou & Kostopoulos (2006) included them all in a single species but acknowledged that “the populations of small-medium molar size prevail during MN11-12, while the medium-large sized ones are more common during MN12-13”. The M3 from Str-2 is among the largest in this group, being surpassed only by a few teeth from the late Turolian of Lubéron and Dytiko, but some teeth that are certainly earlier are almost as large; these include teeth from Nikiti-1 ( Kostopoulos 1994), Çorak Yerler, and a maxilla from Kopran in the NHMW, the M3 of which is 44.4 mm long. Although it is probably true that differences in size and proportions of the third molars do exist between the various populations, sample sizes are small, and most confidence intervals of the mean values overlap ( Fig. 12). In particular, the distinction between a “small-medium” and a “medium-large” group ( Sylvestrou & Kostopoulos 2006) looks to us artificial, as neither the m3s nor the M3s ( Fig. 12; also Sylvestrou & Kostopoulos 2006: respectively figs 6, 7; 2009: respectively figs 4, 3) show any clear distinction between two groups, and there is certainly no simple relationship between size and chronology. The fact that suids have been so useful (with much larger sample sizes!) in East- African Plio-Pleistocene biochronology should not lead us to believe that they are bound to play the same role in the Eurasian Upper Miocene.

Figures

FIG. 3. — Fossil mammals from the Miocene of Strumyani (SW Bulgaria): A-C,?Tetralophodon atticus (Wagner,1857); A, DP2 FM-2027, occlusal view;B, dp2 FM-2799, lingual view,C, DP3 FM-2798,occlusal view; D, Dihoplus pikermiensis (Toula, 1906), dorsal view of symphysis FM-2470;E, Microstonyx major (Gervais,1848),maxilla FM-2801;F, G, Dorcatherium cf.puyhauberti Arambourg & Piveteau,1929, mandible FM-2741 in occlusal (F)and lateral (G) views;H, Palaeotragus rouenii Gaudry,1861,mandible FM-2778;I, Miotragocerus (Pikermicerus) gaudryi (Kretzoi,1941), mandible FM-2103; J, Cervidae gen.et sp. indet., mandible FM-2100. Scale bar: A-C,F-J, 7.5 cm; D, 30 cm; E, 10 cm.