Prostrepsiceros rotundicornis ( Weithofer, 1888 )

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 : 475-476

Prostrepsiceros rotundicornis ( Weithofer, 1888)

The best preserved specimen is a frontlet with most of the right horn-core and the base of the left one, FM-2739 ( Fig. 13J ; measurements: Table 4). FM- 2765 and 2766 are horn-cores in bad condition. This taxon is also represented by a frontlet from Str-1, FM-2779 ( Fig. 13I ). The neurocranium was certainly little inclined on the face, as the frontal is little bent. The supra-orbital foramina open at the lateral sides of large depressions that nearly meet at a mid-frontal suture; the latter is slightly raised and open, as is also the fronto-parietal one. There is a large post-cornual fossa. The orbital rims are prominent.

The pedicles are extremely short, as the horncores rise directly from the frontal bone. They are inserted rather uprightly, diverge from the very base, and the divergence increases upwards before decreasing in the second half. They are strongly spiralled but lack keels, although grooves run along their lateral surface.

These frontlets obviously belong to a group of Prostrepsiceros Major, 1891 whose horn-cores virtually lack keels, and which includes P. rotundicornis and P. fraasi (Andree, 1826) . The former species was defined at Pikermi ( Weithofer 1888; Gaudry 1862 - 1867; Pilgrim & Hopwood1928), the latter at Samos ( Andree 1926). The boundary between these species, and their occurrences in other localities have long been debated ( Gentry 1971; Bouvrain 1982) but recent discoveries and taxonomic revisions tend to support the distinction ( Kostopoulos 2005, 2006). Prostrepsiceros fraasi is larger, has a more strongly angled face on the neurocranium, less salient orbital rims, shallower post-cornual fossa, and more divergent horn-cores. It occurs at Samos, Maragha, and perhaps Perivolaki (although Kostopoulos [2009b] now believes that the Perivolaki form is closer to P. houtumschindleri (Rodler & Weithofer, 1890)) , while P. rotundicornis is present at Pikermi, Halmyropotamos, AkkasdaĞI, Ravin des Zouaves 5 ( Gentry 1971; Bouvrain 1982; Kostopoulos 2005, 2006) and at Vozarci in the Republic of Macedonia (FYROM). Further finds are needed before the issue can be settled, because it may look hard to accept the occurrence of two contemporaneous and partly sympatric closely related species. If the distinction between these two species is accepted, the characters of the Str-2 frontlet clearly align it with P. rotundicornis . Both species are best known from sites similar in age to Pikermi, although some records may be earlier.

Two mandibles, FM-2332 and 2331 ( Fig. 13D ), differ from those assigned above to Palaeoreas by their longer premolar row ( Table 5), but they are otherwise little different, and their assignment to Prostrepsiceros is tentative.

Figures

FIG. 13. — Fossil mammals from the Miocene of Strumyani (SW Bulgaria): A-C, F, G, Palaeoreas lindermayeri Wagner, 1848; A, skull FM-2738, front view; B, mandible FM-2744; C, mandible FM-2783; F, frontlet FM-2740; G, frontlet FM-2780; D, I, J, Prostrepsiceros rotundicornis (Weithofer, 1888); D, mandible FM-2331; I, frontlet FM-2779; J, frontlet FM-2739; E, Palaeoryx sp., tooth row p2-m2 FM-2251; H, Tragoportax sp., skull FM-2094. Scale bar: A, G-J, 20 cm; B-E, 5 cm.