Hipparion aff. sebastopolitanum, Borissiak, 1914

Koufos, George D. & Sen, Sevket, 2016, Equidae, Geodiversitas 38 (2), pp. 225-243 : 228-232

Hipparion aff. sebastopolitanum

LOCALITY. — Küçükçekmece, Turkey.

AGE. — Late Vallesian, MN 10; Late Miocene.

MATERIAL. — See Table 1.

MEASUREMENTS. — See Table 1.

DESCRIPTION

Mandible

Three mandibular fragments (MNHN.F.TRQ30, TRQ31, TRQ32) are the most complete remains in the Küçükçekmece hipparion sample;TRQ30 preserves the complete cheek tooth row, TRQ31 the p3-m3 row and TRQ31 the p3- m1row ( Fig. 3 ). The mandibular ramus of TRQ30 is deep and thick, the symphysial part is broken but the beginning of symphysis is well distinguished, indicating a possible short muzzle. The tooth row is elongated (p2-m3 = 148.5 mm) suggesting a large hipparion.The teeth are worn, especially in MNHN.F.TRQ31, TRQ32 (VIth wearing stage).

Upper cheek teeth

The upper cheek teeth have richly plicated enamel in the fossette’s borders with thin and deep plis (Fig. 4). The plication number (sum of plis in the fossette’s borders + pli caballin) ranges from 14-27 (mean 19.8) plis in the P3,4 and it is 16 in the M1,2. The pli caballin is double-triple and the main one is large. The protocone is free, oval, lingually flattened in some teeth and bears a reduced spur; the latter is strong in the unworn-little worn teeth (MNHN.F.TRQ12, TRQ15). In the much worn teeth the protocone becomes more rounded and is connected with the protoloph (TRQ19). The distal hypoco- nal groove is deep, V-shaped but the wear gradually reduces its depth and breadth (TRQ19). A clear lingual hypoconal groove can be distinguished in the little worn TRQ24 and a faint one in the wornTRQ7. The height of the unworn M1,2 TRQ15 is 54 mm and its hypsodonty index (tooth length at 1 cm above the roots × 100/height) is 38.3.

Lower cheek teeth

The p2 bears an elongated paraconid (anterostylid) pointed in MNHN.F.TRQ33 and more rounded inTRQ30 ( Figs3A ; 4). The premolars are short and wide in comparison to the molars. The parastylid is well developed in all teeth and it is continuous across the mesial border of the teeth.The metaconid is ellipticalrounded. The metastylid is triangular and the entoconid almost squarish with a small spur in the mesio-buccal corner. There is no ectostylid. The m 1,2 have a small protostylid restricted to the lower part of the tooth; despite its advanced attrition, it remains isolated and unconnected with the parastylid in the m1,2 of TRQ30, TRQ31 but in the less worn teeth ofTRQ32 it is not observable. The ectoflexid of the molars is deep and reaches the posterior border of the preflexid (TRQ30) or it is in touch with the linguaflexid. The pli caballinid is very weak in the molars. The pre- and post-flexid borders are plicated or crenulated.Two isolated m3, TRQ41 ( Fig. 5 ) and KÇ25, might belong to this hipparion. The eruption way of the m 3 in equids affects the value of its length and makes difficult a precise comparison.The size of TRQ41 and KÇ25 is similar to that ofTRQ30, TRQ31 and both can be included to this hipparion.

MNHN.F.TRQ15 MNHN.F.TRQ38 MNHN.F.TRQ40 MNHN.F.TRQ44

FIG. 4. — Hipparion aff. sebastopolitanum, Küçükçekmece , Turkey, Vallesian, upper and lower cheek teeth. The position of the teeth is given in Table 1. Scale bar: 4 cm.

MNHN.F.TRQ106 MNHN.F.TRQ14 MNHN.F.TRQ17 MNHN.F.TRQ41

Metapodials

The metapodials of form-A dominate in the Küçükçekmece sample but are all incomplete ( Fig. 6 ); the distal fragment of the McIII MNHN.F.TRQ21 is not included in the sample as it is strongly eroded and its measurements are not reliable. The sample of proximal and distal fragments of the McIII are close in size to H. mediterraneum Roth & Wagner, 1854 from Pikermi ( Fig. 2 ) but their length is unknown. The keel index (M12 × 100/M13) is on average 117 vs 117 for H. primigenium from Höwenegg, 115 from Akçaköy and 116 from Eppelsheim; for the strong keel bearing metacarpals of H. mediterraneum from Pikermi and H. philippus from Nikiti 2 the keel index is 119 and 123 respectively The MtIII is short and relatively robust; the slenderness index (M11 × 100/M1) is on average 15.3 vs 16.2 for H. primigenium from Höwenegg, 14.3 from Akçaköy and 15.2 from Vienna Basin. The same index for the slender metatarsals of H. mediterraneum from Pikermi and H. philippus from Nikiti 2 is 13.7. The keel index for MtIII is on average 121 vs 121 for H. primigenium from Höwenegg and Akçaköy, and 122 from Vienna Basin; the keel index of H. mediterraneum from Pikermi and H. philippus from Nikiti 2 with strong keel is 127 on average [data taken from Koufos (1987), Bernor et al. (1997, 2003) and Koufos & Vlachou (2016)]. Thus, the metapodials of the Küçükçekmece form-A are short and relatively robust with weakly developed keel.

Figures

FIG. 3. — Hipparion aff. sebastopolitanum, Küçükçekmece,Turkey,Vallesian:A, right mandibular fragment with p2-m3 (MNHN.F.TRQ30) in lingual (A1), labial (A2) and occlusal (A3) views; B, right mandibular fragment with p3-m3 (TRQ31) in lingual (B1), labial (B2) and occlusal (B3) views; C, left mandibular fragment with p3-m1 (TRQ32) in lingual (C1), labial (C2) and occlusal (C3) views. Scale bars: 5 cm.

FIG. 5. — Hipparion aff.giganteum, Küçükçekmece,Turkey,Vallesian, upper and lower cheek teeth; the specimens MNHN.F.TRQ14, TRQ17, TRQ41, and TRQ106 cannot be certainly attributed to one of the Küçükçekmece hipparions. The position of the teeth is given in Table 1. Scale bar: 4 cm.

FIG. 6. — Hipparion aff. sebastopolitanum and H. aff. giganteum, Küçükçekmece, Turkey, Vallesian, postcranial remains. The determination of the bones is given in Table 1. Scale bar: 5 cm.

FIG. 2. — Separation of the Küçükçekmece postcranial remains of hipparions. A, B, Simpson’s log-ratio diagrams comparing the third metacarpals (A) and third metatarsals (B); reference:H. mediterraneum Roth & Wagner,1854, Pikermi (Koufos 1987); C-E, principal component analysis separating the astragalus (C), first phalanx (D) and second phalanx (E). Abbreviations: see Figure 1.