Stephanorhinus pikermiensis ( Toula, 1906 )

Antoine, Pierre-Olivier & Saraç, Gerçek, 2005, Rhinocerotidae (Mammalia, Perissodactyla) from the late Miocene of Akkașdağı, Turkey, Geodiversitas 27 (4), pp. 601-632 : 616-618

Stephanorhinus pikermiensis ( Toula, 1906)

Rhinoceros schleiermacheri pikermiensis Toula, 1906: 34 , pl. 2, fig. 2.

Rhinoceros schleiermacheri samius Toula, 1906 : pl. 2, fig. 3.

Rhinoceros (Ceratorhinus) schleiermacheri var. orientalis Schlosser, 1921 : pl. 1, fig. 8.

Stephanorhinus pikermiensis – Heissig 1996: 341-343, 347, text-fig. 27.2.

MATERIAL. — Left worn M1, AK5-w.n.; distal end of a right radius, GOK-14; right broken and eroded magnum, GOK-12; medial part of a left astragalus, AK6-57; left mesocuneiform, AK5-197; left MtII and MtIII from the same individual, AKA-45; (x) distal end of a left MtII (distal APD = 37), AK5-2; left MtIII, AK3-65.

DESCRIPTION AND COMPARISON

The remains belong to at least two individuals (e.g., two left MtIII are preserved).

Dentition

The M1 AK5-w.n. is much worn, so most of the morphological features have disappeared. The enamel is thin and wrinkled at the neck. The roots are joined, but not as thickly as it could be expected from an old individual. There is neither labial nor lingual cingulum. The crochet is simple. The lingual cusps are separate. There is neither anterior constriction isolating the protocone, nor antecrochet. No crista is preserved at this stage of wear. The hypocone is devoid of any groove. This tooth (L = 49; ant. W = 74; post. W = 65; H = 13) is very wide with respect to the M1 of the skull AK4-212 attributed to C. neumayri (see above; Appendix: Table 2). Indeed, these dimensions and structures are similar to the M1 from the skull NHM M 10144 ( S. pikermiensis, Pikermi ; Geraads 1988: pl. 2, fig. C).

Radius

Only a distal end is preserved (GOK-14; Appendix: Table 26; Fig. 5A ). It is large, with an oblique distal border in anterior view (getting lower medially than laterally). The tuberculum dorsale is very reduced and smooth. Thus, the anterior side is flat transversely. The single lateral ulna-facet is crescent-like, vertical and oblique sagittally. The posterior side is keeled and deepened by a wide fossa beginning 3 cm above the distal articulation.The scaphoid-facet is visible in anterior view on a considerable height. This facet has a sigmoid sagittal cross section. Its posterior expansion forms a high rounded triangle. The semilunate-facet is wide, concave antero-posteriorly and slightly convex transversally. There is no pyramidal-facet.

Magnum

The posterior tuberosity is lacking in the only specimen (GOK-12; Appendix: Table 27; Fig. 5B, C ), which is badly damaged. The anterior side is roughly square, without a salient central tubercle (contrary to GOK-11, referred to C. neumayri ). In proximal view, the scaphoidfacet is narrow. The semilunate-facet has a semicircular outline in lateral view: there is no anterior inflection as in C. neumayri . The proximal process is very large, with a huge diameter, and rounded. This facet reaches the anterior side of the bone. It is separate from the unciformfacet by a shallow groove. On the medial side, there is a shallow anterior indentation between the scaphoid- and the McII-facets. The former forms a flat and oblique sagittal stripe, nearly rectangular. Distally, the McIII-facet is wide and saddle-shaped, without posterior tapering.

Astragalus

The only specimen is a broken astragalus, lacking the lateral part (AK6-57). The proportions are similar to those from C. neumayri (see above; Appendix: Tables 17; 28). The size is comparable (H, APD, TD) but some features differ anyway. The medial lip of the trochlea is identical to that of C. neumayri , except in the facet for the malleolus medialis: this articular stripe for the tibia is much wider in AK6-57. It forms a broad stripe, with a brutal thinning in its proximal third. The lip is also smoother (sharp ridge in C. neumayri ). The collum tali is lower than in C. neumayri , especially medially, where the trochlea nearly reaches the proximal tip of the navicular-facet. The medial tubercle is very different in the two taxa: it is more laterally projected, forming a sharp and salient tubercle in AK6-57 (thin, with a vertical medial border in C. neumayri ); the most striking difference concerns the height of this tubercle. It does not reach the distal third of the bone in AK6-57, while it reaches the half of it in C. neumayri . On the posterior side, some differences appear. The calcaneus-facet 2 is large and circular, nearly flat, whilst it is high, oval and transversally strongly convex in C. neumayri . Furthermore, this facet joins the facet 3, contrary to C. neumayri , where both are separate – the astragalus-facets 2 and 3 are also separate on the calcanei attributed to C. neumayri (see above). On the distal side, the navicular-facet has the same outline, but its posterior tip is marked by a high and brutal break (AK6-57), visible in anterior view. This facet is concave transversally whereas it is nearly flat in C. neumayri . The cuboid-facet is broad, short, and it tapers posteriorly in AK6-57. The distal articulation is narrower (TD) in AK6-57 than in C. neumayri .

Further comparison with 30 astragali attributed to C. neumayri , three specimens identified as D. orientalis ( Schlosser, 1921) by Saraç (1994) from several Turolian localities of Turkey (MTA collections), and the material from Pikermi (Gaudry Collection, MNHN), confirms the consistency of these differences. Furthermore, the astragalus of “ D. orientalis ” from the Turolian of Shanxi ( Ringström 1924: 15, text-fig. 10) is identical to AK6-57, at least in anterior view (dimensions, proportions, structures).

Mesocuneiform

AK5-197 has the same size as AK5-637, attribut- ed to C. neumayri (Appendix: Tables 21; 29). The main differences consist of the triangular proximal outline (semi-circular in AK5-637), the presence of a tubercle on the antero-medial side (smooth in AK5-637), the low and drop-like entocuneiform-facet (semi-circular in AK5-637), and the high and short ectocuneiform-facet (low and long in AK5-637).

MtII

Although bearing similar dimensions with the MtII referred to C. neumayri (Appendix: Tables 23; 30), the specimens (AKA-45, AK5-2) somehow differ from the latter: the entocuneiformfacet is lower and circular; the postero-lateral facet joins the proximal facet; both anterior and posterior lateral facets are split into two equal parts by a median horizontal groove; the posterior facet is higher and the sub-facets are more distinct. Both distal halves (anterior and posterior) correspond to the MtIII, thus pointing out the presence of high MtII-facets on the MtIII.

MtIII ( Fig. 5D, E )

AK3-65 and AKA-45 display similar proportions with the MtIII referred to C. neumayri (Appendix: Tables 24; 31). Some morphological differences can anyway be observed: in proximal view, the anterior border of the proximal articulation is depressed while the lateral border is strongly concave; the proximal end is as deep (APD) as wide (TD); the MtII-facets are high and nearly joined; the MtIV-facets are fused; the distal trochlea is strongly thickening medially; the intermediate relief is high and acute; there is no distal widening of the diaphysis.

DISCUSSION

Toula (1906) established Rhinoceros schleiermacheri pikermiensis on the basis of some specimens from Pikermi. Later, Rhinoceros (Ceratorhinus) schleiermacheri var. orientalis was described on similar remains discovered in Veles, Pikermi and Samos ( Schlosser 1921). We agree with Geraads (1988), assuming that these fossils are conspecific, especially those from Pikermi, the type locality of Rhinoceros schleiermacheri pikermiensis . Thus, and following the current International Code of Zoological Nomenclature ( ICZN 1999), the principle of priority states that the valid name is R. pikermiensis Toula, 1906 .

On the other hand, we do follow the opinion of Heissig (1996) and Fortelius et al. (2003) concerning its assignment to the genus Stephanorhinus Kretzoi, 1942 , under the name Stephanorhinus pikermiensis ( Toula, 1906) , rather than to the genus Dicerorhinus Gloger, 1841 . The type species of Dicerorhinus and Stephanorhinus Kretzoi, 1942 are D. sumatrensis (Fischer, 1814) and S. etruscus (Falconer, 1859) , respectively. As a preliminary result of an unpublished cladistic analysis including most one-horned and twohorned fossil and recent rhinocerotine species (sensu Antoine et al. 2003), at least six synapomorphies differentiate the clade [ S. etruscus , S. pikermiensis s from Dicerorhinus sumatrensis : a small processus paraoccipitalis, a thick protocone on P2, a constricted metaloph on P2-4, a spurlike paralophid and a reduced paraconid on p2, and the presence of vertical roughnesses on the ectolophid of d2-3 support robustly the Stephanorhinus clade and prevent any generic assignment of R. pikermiensis Toula, 1906 to Dicerorhinus . However, the phylogenetic relationships of Stephanorhinus pikermiensis and Ceratotherium neumayri would probably be resolved by a thorough study of the whole rhino material from Pikermi (e.g., the Gaudry collections, MNHN).

Figures

FIG. 5. — A-E, Stephanorhinus pikermiensis (Toula, 1906), AkkaSdağı (Anatolia, Turkey), middle Turolian; A, distal end of a right radius (GOK-14), posterior view, displaying the diagnostic horizontal ridge; B, C, right magnum, lacking the posterior tuberosity (GOK-12); B, medial view; C, anterior view; D, E, left MtIII (AKA-45); D, anterior view; E, lateral view. Notice the fusion of the MtIVfacets, visible in E; F, G, Chilotherium sp., AkkaSdağı (Anatolia, Turkey), middle Turolian, left calcaneus (AK6-60); F, antero-medial view; G, posterior view. The Y-shaped vascular print is noticeable in G. Scale bar: 5 cm.