Ceratotherium Gray, 1867

Antoine, Pierre-Olivier & Sen, Sevket, 2016, Rhinocerotidae and Chalicotheriidae (Perissodactyla, Tapiromorpha), Geodiversitas 38 (2), pp. 245-259 : 248

Genus Ceratotherium Gray, 1867

TYPE SPECIES. — Ceratotherium simum (Burchell, 1817) by original designation ( Gray 1867: 1027).

Ceratotherium neumayri (Osborn, 1900) ( Fig. 1 E-M)

Rhinoceros pachygnathus – Malik & Nafiz 1933: 45, 46.

Diceros aff. primaevus – Nicolas 1978: 456.

Diceros cf. neumayri – Nicolas 1978: 456.

MATERIAL EXAMINED. — MNHN.F.TRQ343, right M1 without ectoloph; TRQ360, right radius, proximal fragment; TRQ327, right Mc2; TRQ333, right calcaneus; TRQ334, right calcaneus, fragmentary and eroded.

DESCRIPTION

Upper dentition

The M1 MNHN.F.TRQ343 is worn, eroded, and largesized (L>52; antW>60; postW>52). The ectoloph is broken. Enamel is worn out. The occlusal pattern is simple, with a sigmoid protoloph devoid of constrictions, a simple sagittal crochet adjacent to the metaloph-ectoloph junction, and a short transverse metaloph ( Fig. 1E ). At this wear stage, the lingual valley, sigmoid in outline, is obturated lingually, due to connected but not fused protocone and hypocone. The protocone is much more developed than the hypocone. There is no lingual cingulum. Lingual roots are short and coalescent.

Postcranial skeleton

MNHN.F.TRQ360 is a proximal fragment of a right radius (proxTD = 99; proxAPD = 59), badly preserved (with a corrugated aspect; Fig. 1F, G ). In proximal view, the anterior border is concave ( Fig. 1F ). The lateral and the posterolateral borders connect through a right-angled ridge. The lateral humerus-facet is much less developed sagittally than its medial counterpart. In anterior view, these facets form a 140° dihedron, pointing to a “diabolo-like” humeral trochlea. The proximal head is much wider than the diaphysis ( Fig. 1G ). The insertion for the m. biceps brachii is delimitated by a rough surface, but without any fossa. In posterior view, the ulna-facets are badly preserved, being the medial one high and crescent-like.

The Mc2 MNHN.F.TRQ327 is quite slender (L = 147; proxTD = 40; proxAPD = 42; diaDT = 38; diaAPD = 19; distTD = 38; distAPD = 38.5), with small proximal and distal articular heads ( Fig. 1H ). In proximal view, the bone has a triangular outline ( Fig. 1I ). The trapezoid-facet is convex sagittally and concave transversely, with a trapezoid outline. The magnum-facet is flat, sub-vertical and kidney-shaped. The Mc3-facets, badly preserved, were independent. There is no trapezium-facet. The diaphysis is sagittally compressed, slightly curved and concave medially in anterior view, with no distal widening. The distal end is as deep as wide (APD = TD) and wider posteriorly than anteriorly (strong antero-medial constriction). In distal view, the anterior border is slightly convex, the lateral border is straight and at a right angle with the former. The posterior border is W-shaped, with a medial lip deeply concave and a sharp keel restricted to the posterior half of the articulation ( Fig. 1J ).

The calcanei MNHN.F.TRQ333 (complete; Fig. 1 K-M) and TRQ334 (fragmentary and eroded) have similar shape and dimensions and we therefore consider them as characterizing a single taxon. They are robust, with massive tuber calcanei (TRQ333: L = 119;TD = 67; APD = 66). There is no fibula-facet but a large almond-shaped tibia-facet (TRQ333; Fig. 1M ). The astragalus-facet 1 has a falciform outline in lateral view, with no obvious postero-distal expansion. The facet 2 is subcircular ( Fig. 1K ) and nearly flat (subconcave). The facet 3 is smaller and almond-shaped. All three facets are independent one from another ( Fig. 1K ). The sustentaculum tali is thick (APD), but not so wide (TD) with respect to the dimensions of the bone ( Table 1). The proximal tip of the tuber calcanei is as deep (APD) as the processus in lateral view ( Fig. 1M ). The posterior border of the calcaneus is straight in lateral view. The cuboid-facet, on the distal side, is saddle-shaped, with a kidney-like outline ( Fig. 1K ). The insertion for the m. fibularis longus forms a smooth tubercle sagittally elongated.

DISCUSSION

Dental and postcranial remains from Küçükçekmece West closely resemble those of C. neumayri from the late Miocene of eastern Mediterranean, in terms of shape. Their dimensions, perfectly matching those originating from Vallesian localities (e.g., Karacaşar, MN10; Antoine et al. 2012), are 10 to 25% smaller and somewhat slenderer than those of specimens from Turolian localities, such as Akkaşdağı, Samos, or Pikermi ( Geraads 1988, 1994; Kaya & Heissig 2001; Antoine & Saraç 2005). Moreover, the presence of a strong lateral tuberosity on the radius, the absence of a trapezium-facet and of a longitudinal crest on the posterior surface of the diaphysis on the Mc2, and the low development of the tuber calcanei on the calcaneus discard any referral of the concerned specimens to Dihoplus pikermiensis (Toula, 1906) , another conspicuous two-horned rhinocerotine from the late Miocene of eastern Mediterranean ( Geraads 1988; Giaourtsakis 2009; L. Pandolfi pers. comm. 04/2016)

Figures

FIG. 1. — Tapiromorph perissodactyls from the upper Miocene locality of Küçükçekmece, Thrace, Turkey: A-D, Ronzotherium sp. (reworked); MNHN.F.TRQ355, left m1 or m2 in occlusal (A), lingual (B), labial (C), and posterior views (D); E-M, Ceratotherium neumayri; E, TRQ343, right M1 in occlusal view; F-G, TRQ360, right radius in proximal (F) and anterior views (G); H-J, TRQ327, right Mc2, in anterior (H), proximal (I), and distal views (J); K-M, TRQ333, right calcaneus, in distal (K), anteroproximal (L), and medial views (M). Scale bar: A-E, 20 mm; F-M, 30 mm.