Hipparion cf. longipes Gromova, 1952

Koufos, George D. & Vlachou, Theodora D., 2005, Equidae (Mammalia, Perissodactyla) from the late Miocene of Akkaşdağı, Turkey, Geodiversitas 27 (4), pp. 633-705 : 648-665

Hipparion cf. longipes Gromova, 1952

LOCALITY. — Akkaşdağı, Keskin, Turkey.

AGE. — Middle Turolian, MN 12 (late Miocene).

MATERIAL. — Left maxilla with P2-M3, AK7-69; right maxilla with P2-M3, AK7-70; 19 distal parts of humerus, AK2-16, 101, 232, AK3-91, 148, 226, AK5-177, 391, 464, AK5-83, AK6-21, AK7-2, 3, 47, 89, AK11-3, 50, 51, 111; radius+ulna, AK2-234; 2 radii, AK3-259, AK11-122; 2 proximal parts of radius+ulna, AK3-214a-b, AK5-221; proximal part of radius, AK5-84; 9 third metacarpals, AK2-393, AK3- 1, 139, 260, AK5-478, 479, AK6-107, 273, AK14- n.n.; 2 McII+McIII+McIV, AK2-244a-c, 24; proximal part of McIII+carpals, AK5-220; proximal part of McII+McIII+McIV, AK4-98; distal part of tibia+tarsals+MtII+MtIII+MtIV, AK11-99a-i; 17 distal parts of tibia, AK2-19, 262, AK3-7, 157, 268, AK5-400, 402, 470, 471, 555, AK6-183, 221, 256, AK12-43, 44, 45, AKK-274; astragalus+calcaneum, AK2-103; 30 astragali, AK2-103, 25, 264, AK3-20, 21, 103, 104, 228, 270, AK4-25, 28, 30, 32, 156, AK5-99, 169, 170, 175, 403, 582, 583, 580, AK6-12, 112, 149, 214, 215, AK7-137, AKK-167, 170; 5 calcanei, AK4-157, AK5-65, 178, 130, 131; 2 MtII+MtIII+MtIV, AK11-136, 137; 12 third metatarsals, AK2-1, 3, 242, 400, AK3-86, 88, AK4- 165, AK5-72, 73, 153, AK14-4, 11; 7 proximal parts of MtIII, AK2-6, AK3-3, AK4-1, 11, 35, 166, AK7-1; 4 distal parts of MtIII, AK3-141, AK5-156, AK11-43, AK13-16; PhI+PhII, AK4-103; 2 first phalanges, AK5-587, AK5-115; 5 second phalanges, AK3-163, AK4-16, 178, AK6-277, AKK-188; 4 third phalanges, AK5-418, AK7-97, 113, AK11-120; part of a third phalanx, AK6-49.

DESCRIPTION

Dentition

The upper toothrow is long with elongated and narrow teeth which are little worn; the M3 is just erupted and unworn ( Fig. 13 ). The P2 has elongated anterostyle, bended lingually; the fossettes are closed. In the P3, 4 the mesiolabial part of the postfossette is still in touch with the mesostyle’s enamel but this is due to the early wearing stage. The enamel plication is rich with deep and narrow plis; the mean plication number is 21.0 for the premolars and 20.5 for the molars. Both studied maxillae are at the first wearing stage, and this means that the enamel plication number will increase somewhat in the second wearing stage. The protocone is elliptical and flattened lingually, especially in the premolars. In the P2 it bears a “spur”. The pli caballin is strong, double in the premolars and simple in the molars. The hypocone is elongated and angular with deep and open distal hypoconal groove, while a slight lingual hypoconal groove is also present, especially in the premolars.

Postcranials

The postcranials of this hipparion are large and slender. The metapodials are very elongated and slender ( Fig. 14 ). The metacarpal is relatively long with narrow epiphyses. The index Length McIII × 100/Length radius is 80, and the robusticity index is 14.7, both indicating a slender metacarpal form. The keel index (m12 × 100/m13) of the studied metacarpal is 122.8 indicating a relatively prominent keel (not well prominent). Similarly the metatarsal is very long and slender. The robusticity index is 13.5 confirming its slenderness, and the keel index (m12 × 100/m13) is 126.9 indicating also a relatively prominent keel.

COMPARISONS

A large-sized hipparion from Pavlodar ( Kazakhstan) having very long and slender metapodials was described under the name H. longipes by Gromova (1952). The type collection of H. longipes includes only isolated teeth ( Gromova 1952). Two maxillary fragments from Akkaşdagwı can belong to this species. Their toothrow length varies between 162.5 and 169.0 mm, while in H. brachypus Pikermi it varies between 147.0 and 168.3 mm with a mean value of 154.86 mm ( Koufos 1987a). Such a large-sized hipparion with very long and slender metapodials is unknown in the Turolian of Eastern Mediterranean region.

In the original description of the type material from Pavlodar, Gromova (1952) noted that the upper teeth of H. longipes are characterized by their large size, short and wide protocone and moderate enamel plication. In the revision of the Pavlodar material, Forstén (1997) noted that the upper teeth are moderately hypsodont, the protocone is apparently flattened lingually and often preserves a “spur”, the plication number is medium to high (22.7 ± 1.5 plis) and the hypocone has occasionally a hypostylar foramen. The Akkaşdagwı sample has similar morphology and dimensions to those of H. longipes . In Figure 15 the dental dimensions of the studied specimens are compared with H. longipes from Pavlodar (measurements from Gromova 1952 and Forstén 1997), as well as with the large-sized H. brachypus from Pikermi ( Koufos 1987a). There are no significant differences in the dental size between the studied material, H. brachypus from Pikermi and H. longipes from Pavlodar. The Akkaşdagwı form has possibly narrower teeth, but we wonder if this is due to the wearing stage or to the way of measuring. However, the teeth length is close to the maximum values for H. brachypus and closer to H. longipes .

The metapodials of H. longipes from Pavlodar are long and slender ( Gromova 1952). The index Length McIII × 100/Length radius is 80 in Akkaşdagwı sample, while the robusticity index is 14.7 for McIII and 13.5 for MtIII, suggesting elongated and slender metapodials. The corresponding index for H. longipes of Pavlodar varies between 14.5 and 14.9 for McIII and 12.5 and 12.9 for MtIII ( Gromova 1952; Eisenmann F Sondaar 1998). Comparatively to H. longipes from Pavlodar, the metacarpals from Akkaşdagwı are slightly shorter with reduced mid-shaft depth and pronounced supra-articular width (measurements 1, 4, 10 in Fig. 16 ). It is worth mentioning here that the Pavlodar sample is poor (one to two specimens) to appreciate the variation of these characters. One proximal part of metacarpal belonging to a large-sized and slender form is known from the Pliocene (MN 15) locality of Çalta, Turkey. It was first referred to H. longipes ( Heintz et al. 1975) and later to H. cf. longipes (Eisenmann F Sondaar 1998) . This partial metacarpal seems to be larger than the typical H. longipes of Pavlodar and those from Akkaşdagw ı ( Fig. 16 ). The proximal part of a metacarpal from Megalo Emvolon (MN 15) ( Macedonia, Greece) was referred to as H. gracile (Arambourg F Piveteau 1929) . It is a large-sized form with proximal articular width similar to that of the typical H. longipes from Pavlodar, but the proximal articular depth is significantly larger, and similar in that to H. cf. longipes from Çalta ( Koufos et al. 1991). The Akkaşdagwı metatarsal is closer to the typical H. longipes from Pavlodar and to H. cf. longipes from Çalta, but it is shorter and its distal articular depth quite smaller ( Fig. 17 ).

The astragalus and calcaneum are also compared with those of H. longipes . The dimensions of the astragalus are generally smaller than those of the typical H. longipes , while those of calcaneum seem to be similar ( Fig. 18 ).

The similarity of the studied form with H. longipes from Pavlodar is also observable on the logarithmic ratio diagram that compares the first and second phalanges of the Akkaşdagwı form to those of H. longipes . The first phalanx is similar in size to H. longipes from Pavlodar, but it is significantly shorter than that of Çalta ( Turkey) and Megalo Emvolon, Greece ( Fig. 19 ). Moreover, the Megalo Emvolon first phalanx seems to be more slender than that of Pavlodar, Çalta and Akkaşdagwı ( Fig. 19 ). These differences are due either to the age differences between the localities or to the differences between the phalanges of front and hind leg. The second phalanx of the studied form is also very close to H. longipes from Pavlodar ( Fig. 19 ). The Çalta material is again larger than that of the Akkaşdagwı and Pavlodar samples ( Fig. 19 ).

A comparison of both legs of the Akkaşdagw ı material with H. longipes from the type locality of Pavlodar, as well as from Çalta, is given in Figure 20 . It is quite clear from the diagram that the Akkaşdagw ı form is closely related to the type form; their lines are parallel and very close to each other, indicating a similar size. The small differences are possibly due to the scanty material from both localities. On the other hand the Çalta form is significantly larger than the Akkaşdagwı form with relatively narrower metatarsal (measurements 3, 11 in Fig. 20 ). This size difference is possibly due to the younger age of the Çalta material ( Sen et al. 1998a) .

Taking into account all the above mentioned data, the very large and slender form from Akkaşdagwı is morphologically and proportionally close to H. longipes from Pavlodar. However, the unknown skull morphology and the limited dental morphology of H. longipes , as well as the poor material from its type locality cannot allow a certain determination for the studied material. Thus, it is referred to as Hipparion cf. longipes . However, if the presence of H. longipes in the Akkaşdagwı fauna is a fact, it could mean that: 1) H. longipes appeared in Asia earlier than in its type locality Pavlodar which is correlated to late Turolian (MN 13), and survived in Greece and Turkey during Ruscinian; 2) the Turolian H. longipes (Pavlodar, Akkaşdagwı) is smaller in size than the Ruscinian one from Çalta and Megalo Emvolon indicating an evolutionary size increase. However, the poor material referred to H. longipes , and especially the absence of skull, do not allow to testify the previous thoughts about the origin and dispersal of this species.

Hipparion dietrichi Wehrli, 1941 LOCALITY. — Akkaşdağı, Keskin, Turkey.

AGE. — Middle Turolian, MN 12 (late Miocene).

MATERIAL. — Skull, AK3-211; anterior part of the skull with I1-M3 dex and sin, AK2-499; anterior part of the skull with the muzzle and P2-M3 dex and sin, AK3-234; maxilla with P2-M3, AK6-136; maxilla with P2-M3, dex and sin, AK5-n.n.; maxilla with P3- M3, AK11-83; maxilla with dP4-M2 dex and P3-dP4- M2 sin, AK2-498; right maxillary fragment with P2-M3, AK2-46; right maxillary fragment with P3- M3, AK2-172; right maxillary fragment with P4-M2, AK2-175; right maxillary fragment with P3-M2, AK2- 173; right maxillary fragment with P2-P3, AK4-59; left maxillary fragment with P4-M3, AK3-170; left maxillary fragment with P2-M1, AK5-510; right maxillary fragment with P3-M3, AK7-71; maxillary fragment with P4-M3 sin, AK6-137; maxillary fragment with P3-M2 sin, AK14-19; 2 maxillary fragments with M2-M3 dex, AK14-18, AK7-115; 4 mandibles, AK2- 177, 51, AK4-129, AK5-530; left and right mandibular fragment with p2-m3, AK2-357, 358; mandibular fragment with p2-m1 sin, AK2-119; mandibular fragment with p2-m3 sin, AK5-33; mandibular fragment with m1-m3 sin, AK5-645; mandibular fragment with c-m1 dex and m1-m2 sin, AK6-129; 5 distal parts of humerus, AK2-327, AK3-92, AK6-19, 268, AK7-114; humerus+radius, AK6-222; 2 radii, AK5-467, AK7- 49; 4 proximal parts of radius, AK3-n.n., AK5-8a, AK5b-102, AK6-103; 5 distal parts of radius, AK2- 392, AK3-215, AK4-249, AK6-147, AK11-115; 5 third metacarpals, AK3-140, AK5-394, 476, 477, AK6-4; 3 McII+McIII+McIV, AK11-56a-c, 133, 134; 3 proximal parts of McIII, AK3-4, 264, AK11-20; 3 distal parts of McIII, AK2-8, AK5-219, AK7-44; distal part of tibia+astragalus+tarsals+MtII+MtIII+MtIV, AK11-5-13; distal part of tibia+astragalus+calcaneum+navicular, AK6-263a-c; distal part of tibia+astragalus+calcaneum, AK6- 264a-b; 14 distal parts of tibia, AK3-146, AK4-2, 34, AK5-554, 556, 558, 559, AK7-92, AK11-12, 38, 41, 44, 128, AK12- 46; astragalus+tarsals+MtII+MtIII+MtIV, AK6-181; astragalus+calcaneum, AK5-10a-b, AK11-15; astragalus+tarsals, AK2-28a-b; 20 astragali, AK3-19, 153, AK4-14, 101, AK5-98, 168, 173, 404, 581, 584, AK6-10, 111, 113, 148, 220, 314, AK7-11, 50, 136, 137; 9 calcanei, AK2-30, AK2-32, 272, AK4-31, AK5-12, 405, 473, n.n., AK7-112; 8 partial calcanei, AK-2-29, 32, AK3-18, AK4-27, AK5-111, AK11-15, 16, 33; 2 MtII+MtIII+MtIV, AK5-563, AK11-42a-c; 12 third metatarsals, AK2-96, 401, AK5-158, 408, 409, 481, 482, 485, AK5b-n.n., AK6-108, 181, 270; 7 proximal parts of MtIII, AK2-7, AK3-2, 277, AK5- 566, AK6-109, AK12-50, 51; 6 distal parts of MtIII, AK2-9, AK3-85, AK5-157, AK6-8, AK10-15, AK11- 25; PhI+PhII, AK6-274a-b; 7 first phalanges, AK5- 116, 162, 415, 588, AK6-119, 265, AKK-149; distal part of first phalanx, AK6-45; 7 second phalanges, AK2-33, AK5-118, 419, 589, AK5a-121, AK6-159, 266; 3 third phalanges, AK4-15, AK5-496, AK11- 119; part of a third phalanx, AK5-165.

DESCRIPTION

Skull and dentition

The studied form corresponds to the mediumto large-sized hipparion of Akkaşdagwı. Contrary to the abundance and good preservation state of the postcranials, the cranial and mandibular remains are fragmentary. All available skulls

Koufos G. D. F Vlachou T. D.

lack the braincase, and in most of them the muzzle is broken. The most complete skulls are AK3-211, AK2-499 and AK3-234 ( Figs 21-23 ), preserving either the facial region with the preorbital fossa or the muzzle. The AK3-211 is so badly preserved and dorsoventrally compressed that its morphological characters cannot be safely used. Consequently, the description is mainly based on the last two skulls, AK2-499 and AK3-234.

Miocene Equidae from Akkaşdagwı, Turkey

The skull is medium- to large-sized with a very short, wide, U-shaped and deep muzzle. The narial opening is short and its posterior border is situated just above or in front of the P2. The palate is narrow, elongated and quite deep; the index m2 × 100/m13 is 136.4. The preorbital fossa is anteroventrally oriented, relatively narrow and elliptical, moderately deep (no more than 15 mm) with a well marked but no pocketed posterior rim and a faint anterior rim. It is situated far from the orbit and its posterior end is situated quite higher to the orbit ( Fig. 22A ). The lacrymal

Koufos G. D. F Vlachou T. D.

seems to be large but does not invade the preorbital bar. The crista facialis is well developed and its anterior end is placed close to the maxilla, situated above and between the contact of the P4 and M1. The infraorbital foramen is situated above the posterior border of the P2 and just inferior to the anteroventral rim of the preorbital fossa. The orbit is oval-shaped and its anterior border is situated well behind the M3.

The upper cheek teeth are relatively short and wide ( Figs 21C ; 23C ). The P2 is elongated and it has a moderately developed anterostyle directed forward. The fossettes are free and isolated. The emamel plication is moderate with deep and rela-

Miocene Equidae from Akkaşdagwı, Turkey tively wide plis in the moderately worn teeth. The plication number is 12-27 in the P3,4 and 7-19 in the M1,2. The protocone is rounded in the premolars and elliptical in the molars. The pli caballin is long and usually simple to multiple in the premolars, while it is small and simple in the molars. The hypocone is elliptical with well developed and deep distal hypoconal sinus and lingual hypoconal sinus in M3 where it tends to be isolated.

The mandible ( Figs 24 ; 25 ) has a wide snout. The index m2 × 100/m7 is 221.8 indicating a short snout. The symphysis is relatively elongated and deep. The cup seems to be large and wide

Koufos G. D. F Vlachou T. D.

and the insisors are moderately curved. The horizontal ramus has moderate height. The premolars are relatively short and wide having a robust aspect ( Figs 24C ; 25C ). The metaconid and metastylid are elliptical. The enamel at the flexid’s borders is plicated or crenulated. The entoconid is elliptical in all teeth. The ectoflexid is moderately deep in the premolars, separating the pre- and post-flexid, and very deep in the molars touching the lingualflexid. The latter is open, U-shaped and shallow. The pli caballinid is simple in the premolars and simple or absent in the molars. The hypoconulid is well developed especially in the less worn teeth.

Miocene Equidae from Akkaşdagwı, Turkey

Postcranials

The metapodials are relatively long and slender ( Fig. 26 ). The index Length McIII × 100/Length radius is 75.5 indicating a relatively long metacarpal. The robusticity index (m11 × 100/m1) is 16.0 for McIII and 14.3 for MtIII respectively, indicating long and relatively robust metapodials. The facet for cuneiforme II is always present. The keel index (m12 × 100/m13) is 120.4 for McIII and 128.4 for MtIII, indicating a well developed keel. COMPARISONS

H. dietrichi is the best known Old World hipparion and, according to Bernor et al. (1996a), belongs to “ Hipparion s.s. -group” that derives from an Old World form belonging to the “ Hippotherium Complex”. It was originally described from Samos (locality unknown) as Hemihipparion dietrichi (Wehrli, 1941) . Later, it was transferred to the genus Hipparion and for a long time it was considered as a local species of Samos. The main features that characterize the type specimen of H. dietrichi are: medium to large size, short and broad muzzle, short narial opening (above or in front of P2), oval-shaped and relatively shallow preorbital fossa situated quite far from the orbit and far above the facial crest, moderately plicated upper teeth, ovalshaped protocone and elongated and relatively slender metapodials ( Sondaar 1971).

A set of skulls from Samos Q1 and Q4, stored in the AMNH, have been described as H. dietrichi by Sondaar (1971:pl.IIb). Some skulls from Adrianos ravine, stored in the Natural History Museum of Aegean, Samos, were also referred to H. dietrichi by Koufos F Melentis (1984). Later on, the species was recognized in the Turolian localities of “Ravin des Zouaves-5” (RZO), “Prochoma 1” (PXM), “Vathylakkos 1,2,3” (VLO, VTK, VAT) of the Axios Valley and in the locality “Nikiti 2” (NIK) of Chalkidiki, Greece ( Koufos 1987b, c, 1988a; Vlachou F Koufos 2002). All these skulls share more or less the morphology of the type specimen. The Akkaşdagwı skulls seem to be closely related to the sample of H. dietrichi , as they have several morphological affinities and metrical similarities ( Figs 22 ; 27 ). Comparing the Akkaşdagwı form to H. dietrichi from various localities, it has longer muzzle (measurement 1) and narrower preorbital fossa (measurement 35). Overall, the dimensions of the studied sample track those of H. dietrichi from Q1 and the larger toothrow length suggest a larger body mass compared to the rest of the sample ( Fig. 27 ).

Another species closely related to H. dietrichi is H. prostylum which was also referred by Bernor et al. (1996a) to “ Hipparion s.s. -group”. Hipparion prostylum was originally described from Mont Lubéron by Gervais in 1849, and it was also mentioned from Pikermi, Thessaloniki and Middle Maragha ( Bernor 1985;Watabe F Nakaya 1991b) but Koufos did not recognize this taxon neither in Pikermi nor in Axios Valley ( Koufos 1987b). Two badly preserved skulls from Mont Lubéron are stored in the BMNH.One of them, BMNH26617, has an oval preorbital fossa, anteroposteriorly oriented and its anterior rim is well defined. The preorbital bar is long. The posterior border of the narial opening is situated above P2, while the muzzle is short (measurement 1 is 105 mm). These characters are common in H. dietrichi and, comparing the skull of H. prostylum from Maragha either to the type skull of H. dietrichi or to the skulls of H. dietrichi from Axios Valley and Samos, no more differences are observed except the well marked peripheral outline of the preorbital fossa and the short cheek teeth length; in other words, the Maragha H. prostylum seems to be very close to H. dietrichi ( Fig. 27 ; Appendix 2: Table 20). The studied hipparion from Akkaşdagwı shares some characters with both Axios and Maragha samples (Appendix 2: Table 20). In more details, the cheek teeth length is longer than that of H. prostylum and closer to that of H. dietrichi (measurement 31 in Fig. 27 ). Furthermore, the length of the preorbital fossa is comparable to that of H. dietrichi from Q1, but the width and the general morphology of the fossa is similar to that of H. prostylum from Maragha (measurements 33, 34 in Fig. 27 ). Among the above mentioned forms, there are no clear differences in the upper teeth morphology. Taking into account all the above mentioned, either H. prostylum from Maragha and H. dietrichi are closely related forms or they are synonyms and, the small differences in the preorbital fossa morphology are due to intraspecific variation.

Another hipparion species having similarities to the above mentioned forms is H. molayanensis from Molayan, Afghanistan ( Zouhri 1992). Its snout is short, but not as broad as in H. dietrichi and the Akkaşdagwı form (Appendix 2: Table 20). The nasal notch is situated above the anterior part of P2. The skull proportions almost follow those of H. dietrichi and the Akkaşdagwı form ( Fig. 27 ). The preorbital fossa resembles that of H. dietrichi in being shallow, oval-shaped, situat- ed far from the orbit and occasionally well defined posteriorly. Besides these similarities, H. molayanensis seems to have more oval fossa, situated closer to the facial crest and to the maxilla (measurements 34, 36, 38 in Fig. 27 ) and, from this point of view, H. molayanensis is closer to H. mediterraneum from DTK. The dental morphology is similar to that of H. dietrichi , H. prostylum from Maragha and the Akkaşdagwı form (Appendix 2: Table 20). The mandibles from Akkaşdagwı are also very similar to that of H. dietrichi from the various localities ( Fig. 28 ). However, the toothrow of the Akkaşdagwı form is longer than in all the other samples, except H. dietrichi from Samos Q1 (measurements 3, 4, 5 in Fig. 28 ).

The metacarpal of the Akkaşdagwı form is long and slender, and in this feature it differs from H. dietrichi from Northern Greece. In comparison to that from Samos Q1, despite their similar length, it is more robust ( Fig. 29 ). Generally, the metacarpal from Akkaşdagwı has a different pattern than that of H. dietrichi in having mid-shaft width larger than the depth (measurements 3, 4 in Fig. 29 ). In this character, the Akkaşdagwı sample resembles better H. prostylum , but the latter is quite smaller. Unlike metacarpals, the metatarsals from Akkaşdagwı provide great similarities in size with H. dietrichi from Samos Q1 and in general terms similar morphological pattern to the H. dietrichi sample ( Fig. 30 ). The metatarsal from Mont Lubéron, possibly referred to H. prostylum , is quite smaller than the Akkaşdagwı sample and comparable to H. dietrichi from Axios Valley ( Fig. 30 ).

Our knowledge about the size and morphology of the Hipparion limb bones from Central Asia and former USSR is limited either because the material is mixed or because the number of specimens is poor and not well determined. Well studied samples of H. dietrichi are known from Northern Greece (Axios Valley, Chalkidiki) where the species is frequent ( Koufos 1987b, c, 1988a; Vlachou F Koufos 2002). In this area, the chronology of the localities is well established, and the presence of two or three species in each locality with clear size differentiation (smallmedium-large) make the correlation of the limb bones with the skull more certain. So, in these localities the metapodials referred to H. dietrichi are long and slender.

Direct postcranial associations from Samos are unknown. Sondaar (1971) refers some metapodials to H. dietrichi , although he points out that “in the American Museum material it was not possible to find indicators for correlating the bones with the skull”, i.e. his correlation is arbitrary and temporal. The comparison of H. dietrichi from Northern Greece and Samos suggests that although the cranial morphology is homogenous, there is an increase in the size (more robust metapodials, larger toothrow) towards the East. The comparison of the front and hind limb bones of H. dietrichi from various localities ( Fig. 31 ) confirms these results.It is quite clear that the Axios Valley forms are smaller than the Akkaşdagwı and Samos ones, the latter being smaller than that of Akkaşdagwı. The presence in Akkaşdagwı of a skull similar to that of H. dietrichi from Samos Q1,4 and postcranials also similar to those of H. dietrichi , as referred by Sondaar (1971), confirms the determination of the Akkaşdagwı sample as H. dietrichi . The available data about the postcranial skeleton of H. prostylum and H. molayanensis are not precise enough for an accurate comparison. The material of H. prostylum from Maragha belongs to old collections, which are mixed and they cannot be correlated to the stratigraphy. However, according to Watabe F Nakaya (1991a), H. prostylum has possibly large, elongated and probably robust metapodials, as well as large tarsals. Concerning H. molayanensis , despite the fact that all the material was collected from the same locality, we are suspicious about the homogeneity of the postcranial remains, since the presence of another species is not excluded. However, the several similarities between the skulls of H. dietrichi , H. prostylum and H. molayanensis prove a kind of relation between them. The poor information about their postcranial skeleton, the lack of personal observations and a direct comparison between the samples do not permit us to testify their relationship. The three species could be synonyms, representing a widespread form with some local adaptations, or they possibly belong to the same lineage representing forms derived from one another; both assumptions need further study.

Figures

FIG. 13. — Hipparion cf. longipes, Akkaşdağı, Turkey, right upper toothrow, AK7-70, occlusal view. Scale bar: 2 cm.

FIG. 14. — Hipparion cf. longipes, Akkaşdağı, Turkey; A, third metacarpals, AK6-273, AK3-260, AK11-23; B, third metatarsals, AK5- 153, AK2-3, AK3-86. Scale bars: 2 cm.

FIG. 15. — Logarithmic ratio diagram comparing the dimensions of the upper teeth of Hipparion cf. longipes from Akkaşdağı with H. longipes, H. cf. longipes and H. brachypus from various localities. Standard H. mediterraneum, Pikermi, n = 10-32 (Koufos 1987a).

FIG. 16. — Logarithmic ratio diagram comparing the third metacarpal of Hipparion cf. longipes from Akkaşdağı with H. longipes and H. cf. longipes from various localities. Standard H. mediterraneum, Pikermi, n = 12-39 (Koufos 1987a).

FIG. 17. — Logarithmic ratio diagram comparing the third metatarsal of Hipparion cf. longipes from Akkaşdağı with H. longipes and H. cf. longipes from various localities. Standard H. mediterraneum, Pikermi, n = 11-65 (Koufos 1987a).

FIG. 18. — Logarithmic ratio diagram comparing the astragalus and calcaneum of Hipparion cf. longipes from Akkaşdağı with H. longipes from Pavlodar. Standard H. mediterraneum, Pikermi, n = 6-27 (Koufos 1987a).

FIG. 19. — Logarithmic ratio diagram comparing the first and second phalanges of Hipparion cf. longipes from Akkaşdağı with H. longipes and H. cf. longipes from various localities. Standard H. mediterraneum, Pikermi, n = 2-8 (Koufos 1987a).

FIG. 20. — Logarithmic ratio diagram comparing the front and hind legs of Hipparion cf. longipes from Akkaşdağı with H. longipes from Çalta and Pavlodar. Standard H. mediterraneum, Pikermi, n = 3-61 (Koufos 1987a).

FIG. 21. — Hipparion dietrichi, Akkaşdağı, Turkey, skull, AK3-211; A, dorsal view; B, ventral view; C, right toothrow, occlusal view. Scale bars: 2 cm.

FIG. 22. — Hipparion dietrichi, Akkaşdağı, Turkey, skull AK2-499; A, lateral view; B, ventral view; C, right toothrow, occlusal view. Scale bars: 2 cm.

FIG. 23. — Hipparion dietrichi, Akkaşdağı, Turkey, skull AK3-234; A, dorsal view; B, ventral view. Scale bar: 2 cm.

FIG. 24. — Hipparion dietrichi, Akkaşdağı, Turkey, mandible AK5-530; A, ventral view; B, lateral view; C, left toothrow, occlusal view. Scale bars: 2 cm.

FIG. 25. — Hipparion dietrichi, Akkaşdağı, Turkey, mandible AK2-177; A, dorsal view; B, lateral view; C, left toothrow, occlusal view. Scale bars: 2 cm.

FIG. 26. — Hipparion dietrichi, Akkaşdağı, Turkey; A, third metacarpals, AK5-394, AK3-140; B, third metatarsals, AK5-409, AK5-408, AK6-108. Scale bars: 2 cm.

FIG. 27. — Logarithmic ratio diagram comparing the skull of Hipparion dietrichi from Akkaşdağı with other similar forms from various localities. Standard H. mediterraneum, Pikermi, n = 1-9 (Koufos 1987a).

FIG. 28. — Logarithmic ratio diagram comparing the mandible of Hipparion dietrichi from Akkaşdağı with other similar forms from various localities. Standard H. mediterraneum, Pikermi, n = 2-24 (Koufos 1987a).

FIG. 29. — Logarithmic ratio diagram comparing the third metacarpal of Hipparion dietrichi from Akkaşdağı with H. dietrichi from various localities. Standard H. mediterraneum, Pikermi, n = 12-39 (Koufos 1987a).

FIG. 30. — Logarithmic ratio diagram comparing the third metatarsal of Hipparion dietrichi from Akkaşdağı with H. dietrichi from various localities. Standard H. mediterraneum, Pikermi, n = 11-65 (Koufos 1987a).

FIG. 31. — Logarithmic ratio diagram comparing the front and hind legs of Hipparion dietrichi from Akkaşdağı with other forms from various localities. Standard H. mediterraneum, Pikermi (Koufos 1987a).