Hipparion, de Christol, 1832

Ataabadi, Majid Mirzaie, Mohammadalizadeh, Jafar, Zhang, Zhaoqun, Watabe, Mahito, Kaakinen, Anu & Fortelius, Mikael, 2011, Late Miocene large mammals from Ivand (Northwestern Iran), Geodiversitas 33 (4), pp. 709-728 : 713-716

Hipparion sp. large ( Fig. 2 )

LOCALITY. — Quarry 2, Ivand district, north of Tabriz, Iran.

MATERIAL EXAMINED. — Skull ( HMNH-IV 1) and mandible ( HMNH-IV 2) ( Fig. 2 ; Table 1 ).

DESCRIPTION

The skull is quite long and belongs to a large adult male (large canines present). The muzzle is elongated and broad, even though the application of extra material in fixing the broken snout has made the muzzle artificially longer ( Fig. 2 A-C). The narial opening and nasal area have been damaged during excavation and subsequently restored, so details of this area are missing. The POF is very well preserved on the right side and partially filled with sediment on the left side ( Fig.2A ).The POF is far from the orbit,sub-triangular in shape, relatively large and deep, and antero-posteriorly oriented. There is no posterior pocketing. The anterior rim of the POF is well expressed and appears above the medial part of P3. The posterior border of the POF is located above the anterior part of M2. The ventral rim of the POF is not straight, features undulation, and is above the line of the lower border of the orbit.The infra-orbital foramen is at the anteroventral border of the fossa, placed slightly inferiorly. The orbit is round and its anterior border is situated close to the posterior border of M3. The facial crest is very strong and is far from the alveoli and the ventral border of the POF. The anterior border of the facial crest is situated above the medial part of P4.The palate is elongated and wide. The choanae, although filled with sediment, are well preserved. They are wide and their anterior border is situated at the level of contact between M2 and M3.

The upper tooth row is long and complete at both sides, including P2-4, M1-3. All the teeth are moderately worn and the enamel morphology is visible ( Fig. 2D ). The protocone is elliptical and flattened lingually, especially in the molars. The enamel plication is rich (mean plication is 20) with deep plis. The hypocone is elliptical with relatively deep distal hypoconal grooves. The plicabaline is strong, short and single or long and double/multiple.

The mandible is elongated with a narrow snout and cup. The symphysis is short and narrow.The condyle and coronoid processes and the ascending ramus, though not preserved,have been restored ( Fig.2 E-G). The tooth row is long and the teeth are large and wide ( Fig. 2H ). The parastylid is relatively well developed and closed. The metaconid is elliptical to round and the metastylid is rounded. The entoconid is elliptical to round. The ectoflexid is V- or U-shaped and moderately deep and narrow, reaching the middle of the tooth; only in m1 it reaches the linguaflexid. A plicabalinid is present in some of the teeth.

COMPARASION

The hipparion skull from Ivand (HMNH-IV1) has been compared to several species of hipparionine horses, from localities in the eastern Mediterranean and northern Black Sea regions. The bivariate plots of the POB width (distance between the anterior rim of the orbit and the posterior rim of the POF) against the P2-orbit distance, which serve as a useful measure of skull (face) length ( Forsten 1983), appear in Figure 3 . Here, Ivand skull clusters with H. giganteum Gromova, 1952 from Grebeniki, H. brachypus Hensel, 1862 from Pikermi, and Hipparion sp. large from Samos ( Fig. 3A ). The results of a similar plot show the distinction, based

D, H

on this criterion, of the Ivand skull from those of other known hipparion species in Maragheh ( Fig. 3B ), including “ H ”. gettyi Bernor, 1985 ; “ H. ” aff. moldavicum ( H. moldavicum Gromova, 1952 sensu Watabe & Nakaya 1991b ); Hipparion prostylum Gervais, 1849 ; and H. campbelli Bernor, 1985 ( H. urmiense Gabunia, 1959 sensu Watabe & Nakaya 1991b ).

The large-sized skull from Ivand (HMNH-IV1), as the logarithmic ratio diagram shows ( Fig. 4A ), is comparable in its basic dimensions and morphology to H. brachypus from Pikermi ( Koufos 1987b), Hadjidomovo ( Hristova et al. 2003), and Akkaşdaği ( Koufos & Vlachou 2005). However, the Ivand skull has a longer muzzle (M1), which is indeed an artifact of incorrect restoration, and a wider snout (M15). Figure 4B shows that the large-sized skull from the Ivand locality is not comparable in size and morphology to any of the hipparionine horses from Maragheh ( Bernor 1985).

Hipparion brachypus is characterized by large size, an elongated skull with a relatively wide muzzle, and a deep narial opening. The preorbital fossa is oval, antero-posteriorly oriented, well-marked, deeply posteriorly pocketed, and situated far from the orbit. The upper cheek teeth also show rich enamel plication with deep plis ( Koufos 1987a; Koufos & Vlachou 2005; Vlachou & Koufos

2009). Ivand skull ( Fig. 4A ) also partially resembles H. giganteum from Grebeniki, Moldavia ( Gromova 1952). Hipparion giganteum is also a large hipparion with a single, elliptical, and deep POF with strong posterior pocketing, located far from the orbit and facial crest. Nevertheless, the large-sized skull from Ivand has a sub-triangular POF which lacks posterior pocketing. Ivand skull is also comparable to a large-sized skull from Samos (AMNH 22838), described as H. cf. proboscideum ( Sondaar 1971) . This specimen from Samos features more facial height than does the large skull from Ivand. Unlike the type skull of H. proboscideum Studer, 1911 , AMNH 22838 bears a single and deep POF ( Sondaar 1971), which makes it morphologically similar to the H. brachypus skull from Akkaşdaği ( Koufos & Vlachou 2005).

Based on the bivariate plots and log ratio diagrams ( Figs 3 , 4 ), the hipparion skull from the Ivand locality likely belongs to a large-sized Hipparion species of H. giganteum - H. brachypus lineage (“ Hippotherium ” brachypus -“ Hippotherium ” giganteum lineage, sensu Bernor et al. 1996b), previously unknown from the cranial material in NW Iran (i.e. the Maragheh area). We refrain from classifying this specimen at the species level because of some differences in its facial morphology, such as the shape of the POF and lack of posterior pocketing, and its inaccurately restored muzzle. The occurrence of large hipparions (similar to H. brachypus ) in Maragheh was previously evidenced by the presence of medium to large, robust third metapodials ( Watabe & Nakaya 1991a; Tobien in Bernor et al. 1996a, b). Some of these robust metapodials were assigned to H. prostylum , even though they showed greater similarity to the metapodials of H. brachypus from Pikermi ( Watabe & Nakaya 1991a: fig. 15).

Family RHINOCEROTIDAE Owen, 1845

Figures

FIG. 2. — Hipparion sp. large, Ivand locality, NW Iran: A-C, skull (HMNH-IV1) in left lateral (A), ventral (B) and dorsal (C) views; D, right tooth row in occlusal view; E-G, mandible (HMNH-IV2) in left lateral (E), dorsal (F) and right lateral (G) views; H, left tooth row in occlusal view. Broken lines on the fossil specimens delineate extra material used erroneously in restoration (A-C, E-G). Scale bars: A-C, 80 mm; D, H, 30 mm; E-G, 75 mm.

FIG. 3. — Preorbital bar (POB) width plotted against the P2-ORBIT distance, comparing Hipparion sp. large (HMNH-IV1) from the Ivand locality with: A, several other species from the eastern Mediterranean and northern Black Sea regions; and B, Hipparion species from Maragheh (NW Iran).

FIG. 4. — Logarithmic ratio diagrams comparing the skull of Hipparion sp. Large (HMNH-IV1) from the Ivand locality to: A, H. brachy­ pus Hensel, 1862, H. cf. proboscideum, and H. giganteum Gromova, 1952 from localities in the eastern Mediterranean and northern Black Sea regions; and B, “H.î gettyi Bernor, 1985, “H.î aff. moldavicum (H. moldavicum Gromova, 1952 sensu Watabe & Nakaya 1991b), H. campbelli Bernor, 1985 and H. prostylum Gervais, 1849 from Maragheh, NW Iran. Standard, H. primigenium Meyer, 1833, Höwenegg (Bernor et al. 1997).