Pachytragus crassicornis Schlosser, 1904

Kostopoulos, Dimitris S., 2005, The Bovidae (Mammalia, Artiodactyla) from the late Miocene of Akkaşdağı, Turkey, Geodiversitas 27 (4), pp. 747-791 : 772-777

Pachytragus crassicornis Schlosser, 1904

MATERIAL EXAMINED. — Part of skull: GOK- 181+182; frontlet: AK2-503, AK12-70, AK3-200; isolated part of horn-cores: AK7-126, AK7-161, AK6-316, AK4-80, AK4-190; D2-M3: AKB-67; D2- M2: AK11-73; P2-M3: AK2-312, GOK-210, AKB- 95; P3-M2: AK2-157, AK5-204, AKB-69; P4-M3: AK2-156; P2-M1: AK5-445; P2-M2: AK2-312; P3- P4: AK3-194; M1-M3: AK5-426, AK5-293, AKB-70; d2-m2: AK12-80; d4-m3: AK11-59; mandible without vertical rami: AK2-63; i1-m3: AK4-123; p3-m3: AK2-64; p2-m2: AK5-616, AK2-155, AK7-66, AK12-79; m1/2: AK2-159, AK7-104, AK12-35; m3: AK2-325, AK6-68, AK12-81, AK5b-254, AK12-84.

DESCRIPTION

Skull

The opisthocranium is elongated and narrow ( Fig. 18 ; Appendix: Table 10). The occiput is relatively high with strong mastoidal crests. It forms an angle of about 115° with the cranial roof. The foramen magnum is large comparatively to the condyles. The mastoid faces both laterally and posteriorly. The paroccipital processes are probably short and sub-rounded in cross-section. The external auditory meatus is placed just above the upper level of the condyles. The elongate basioccipital is parallel to the flat cranial roof ( Fig. 19A ). Its anterior tuberosities are elongated and parallel to the sagittal plane. The posterior tuberosities are larger and bulge with main axis vertical to the sagittal plane. Between the anterior and posterior tuberosities a weak, wide and shallow central groove runs along the basioccipital. The oval foramen is large, squarish and opens just in front of the anterior tuberosities. The f r o n t o p a r i e t a l a n d i n t e r f r o n t a l s u t u r e s a r e complicated ( Fig. 19B ). The first one forms a forward indentation. The latter one is constricted between the horn-core bases. The frontals form two shallow depressions in the postero-medial side of the pedicles. The supraorbital pits are small, opening at about 40 mm below the horncore base. There is no postcornual groove. The pedicle is rather short with well marked contact with the horn-core. It contains sinuses that however do not continue into the horn-cores. The horn-cores are moderately long (maximal length along the anterior surface at about 280 mm), sabre-like, slightly curved backward and moderately diverged from the sagittal plane ( Figs 18 ; 20A, B ). They are placed above the posterior part of the orbits, slightly tilted backwards (77° with the cranial roof). Their lateral face is flat while the internal one is slightly convex. Their section is elliptically shaped with narrower posterior part at the base but wider towards the apex. The medio-lateral compression increases from the base to the top (Appendix: Table 11). The anteroposterior axis of the horn-core base is oblique comparatively to the sagittal plane (≈ 25°). Discontinuous longitudinal grooves run along the horn-core surface. There is no real keel but a blunt anterodistal constriction is present.

Dentition

Several maxillas and mandibles are assigned to this form (Appendix: Tables 12; 13). The teeth are hypsodont with strong styles and reduced premolar row. P3 is bilobed lingually and longer than P2. Upper molars do not bear basal pillars ( Fig. 21A ).

The mandible is elongate and narrow with shallow rami and moderately long snout. In the best preserved specimen AK2-63 ( Fig. 21B ) the length i1-m3 is about 185 mm, the diastema p2-c is 69.6 mm and the length p2-m3 97.3 mm. The mental foramen opens 46.5 mm in front of p2. The height of the mandibular ramus at p4-m1 level varies between 27 and 32.2 mm (n = 2) with mandibular width at the same point 12.6- 12.9 mm (n = 2).

The lower canine is symmetrical and in contact with the incisors but not very incisiform (rather oval shaped), while its width is slightly larger than that of i3. i2 is as much long as i3 and both are slightly asymmetrical with a weak lingual ridge. i1 is rather symmetrical, more shovel and about 20% larger than i2 ( Fig. 21B ). p2 is simple without paraconid but with strong metaconid and entoconid. p3 has well developed parastylid and paraconid, fused each other at the crown base. The metaconid is independent, but the second valley usually closes at the base due to an elevation of the enamel. The entoconid and the endostylid are elongated and they are fused rapidly together. Lingually, there is a weak furrow separating protoconid from hypoconid. p4 is similar to p3 ( Fig. 21B ) but the paraconid fuses with the parastylid from the first stages of wear, the metaconid is stronger and wider towards the base and the lingual fur- row is stronger. The lower molars have strong stylids, especially metastylid. There is no goat fold or basal pilar (“ectostylid”). The talonid of m3 is single-tubercled with strong postero-lingual stylid.

One of the most impressive characters of the dentition is its hypsodonty. Considering unworn or slightly worn specimens, the hypsodonty index (“Height of posterior lobe/Occlusal length”) is estimated as follows: 113.5 for M1 (n = 1), 91.9- 97.7 for M2 (n = 2), 103.4-121.9 for M3 (n = 3), 122.4-126.9 for m2 (n = 2) and 82-100.4 for m3 (n = 3).

COMPARISON

The morphological features of the Akkaşdagwı skull and frontlets, such as the strong cranio-facial angle, the long and relatively narrow opisthocranium, the sabre-like horn-cores with strong mediolateral compression, the large sinus extending into the pedicle, the small supraorbital foramina not sunken into depressions, the short premolar row and the advanced hypsodonty, clearly align them with the large late Miocene antelopes referred to Protoryx / Pachytragus group. I follow Köhler (1987), Roussiakis (1996), Gentry et al. (1999), and Gentry (2000) in considering Pseudotragus Schlosser, 1904 (synonyms: Microtragus Pilgrim F Hopwood, 1928 ; Sporadotragus Kretzoi, 1941 ) as a valid and distinct genus.

Protoryx enanus Köhler, 1987 from the middle Miocene (MN7) of Turkey and the slightly later Protoryx solignaci Robinson, 1972 from MN8-9 of Tunisia, are quite different from the Akkaşdagwı form, being more primitive either in the horncore or dental morphology and rather smaller in dimensions ( Köhler 1987; Gentry 2000).

In comparison with Protoryx carolinae Forsyth- Major, 1891 from Pikermi, the Akkaşdagwı form differs in the smaller size, longer and narrower opisthocranium, more posteriorly directed condyles, more laterally projected mastoids, more triangularly shaped basioccipital (rather rectangular in P. carolinae ) with less marked groove and bulbous posterior tuberosities (crest like in P. carolinae ), more developed pterygoid process

, P. laticeps Andree, 1926 , Samos;, P. crassicornis, Samos. Abbreviations: DAP, anteroposterior diameter; DT, transverse diameter. Data from Gentry 1971; Köhler 1987; Bouvrain 1994a; and pers. data.

of the sphenoid, flat cranial roof and shorter and more uprightly inserted and almost uncurved horn-cores. Moreover, the horn-cores of P. carolinae show a weaker mediolateral compression ( Fig. 22 ), increasing slightly toward the apexes; the index DT/DAP at the base varies between 70.5 and 84 in P. carolinae versus 65. and 69.7 in Akkaşdagwı, while at 10 cm from the base the same index becomes 69.5-74 versus 60.7-70 respectively.

I do not believe Protoryx carolinae exists in Samos; all the material from the island I have seen is definitely different from the Pikermi one. Therefore, I come closer to Gentry’s (1971) thoughts in placing the forms from Samos (as well as those from Maragha) in a different genus, Pachytragus Schlosser, 1904 . The morphology of the Akkaşdagwı form also matches the diagnostic char- acters of this genus ( Gentry 1971: 244). The recent study of the rich Pachytragus collection from Samos housed in the AMNH (October 2004) let me clarify my previous opinion (exposed in the manuscript reviewed by the referees) and I finally follow Gentry (1971, 2000) in accepting the occurence of two Pachytragus species in Samos. I think Pachytragus latifrons ( Andree, 1926) and Pachytragus crassicornis Schlosser, 1904 are well distinct chrono-stratigraphically: the former is known from the early-middle Turolian levels of Samos (xQx, Q4, Q1) while P. crassicornis is exclusively identified from a certainly younger fossil level (Q5; see also Kostopoulos et al. 2003); the specimen AMNH 20708 from Q1, for which Gentry (1971: 255) suggests stronger similarities with P. crassicornis , belongs with confidence to a young mature male individual of P. laticeps . Interestingly, the braincase dimorphism exhibited in P. latifrons (see discussion in Gentry 1971; Bosscha-Erdbrink 1988) has been bequeathed in P. crasssicornis too (but in a lesser degree): six crania of P. crasssicornis from Q5 have a shorter and broader braincase than the remaining three specimens, which show a long-brained aspect. The character appears to me strongly related to the mechanical response of the skull to the degree of lengthening and backward curvature of the horns and it is worth to be further studied. I do not think the presence of an anterodistal keel is a species related character as suggested by Gentry (1971); although the presence of keel varies significantly (even in the same individual; AMNH 20579), it seems that the character occurs preferencially (or more frequently) in the short-horned individuals of both species (e.g., Pachytragus laticeps , specimen MGL S30 figured in Gentry 1971: pl. III, figs 1, 2; P. laticeps AMNH 22857, 20612, PIM 4, 8, 9; P. crassicornis Schlosser, 1904 : pl. 11, fig. 11; P. crassicornis, AMNH 22943, 22938, 22939).

Both P. laticeps and P. crassicornis populations from Samos comprise rather exclusively male individuals (the female morphology AMNH 20687 [ Gentry 1971: 252 s is much less recognized into the worldwide Samos sample), suggesting gregarious bovids living in large segregated herds. Hence, it seems quite logical to accept that the keel development is more closely linked to the behavioural ecology of these animals, substituting the attractiveness of a long horn.

Pachytragus laticeps and P. crassicornis are very closely related species with the former representing the direct ancestor of the latter. The relatively short and diverged horn-cores, the so-called “mesocephalic” skull structure and the size proportions detected in Akkaşdagwı ( Fig. 22 ) fit pretty well with P. crassicornis . According to Gentry (1971) a distinction of the premolar shortness into the Samos sample is impossible. The premolar/molar ratio of the Akkaşdagwı form varies between 60 and 68 in the upper dentition and 56 and 58 in the lower one. These values are placed safely into the variation of the Samos Pachytragus (the ratio varies between 56 and 69 in the upper toothrow, n = 16 and between 56.6 and 65.7 in the lower, n = 16), being rather larger than in P. carolinae (the upper dentition ratio is about 49 in one of the three known Pikermian specimens; BMNH M11415 ). Interestingly P. carolinae shows a shorter premolar row indicating more advanced dentition than the Samos and Akkaşdagwı forms.

The Maragha Pachytragus , at least the cranium BMNH M3878 (which by the way is the same specimen mentioned and figured by Pilgrim F Hopwood 1928: pl. III, fig. 2 under the register number M3841) shows numerous common features with several Samos specimens but it has certainly stronger horn-cores, more expanded anteroposteriorly. These two characters, as well as the smaller degree of horn-core’s divergence, differentiate it from the Akkaşdagwı form. Among the Maragha material described by Bosscha-Erdbrink (1988) there are, however, several specimens approaching the Akkaşdagwı form both in morphology and dimensions.

Bouvrain (1994a) describes P. laticeps from Kemiklitepe A/B ( Turkey) and Köhler (1987) Protoryx sp. from Kınık ( Turkey). Although the available material from these two localities is quite restricted (some isolated horn-cores and dentitions) the horn-core morphology and proportions ( Fig. 22 ) as well as the dental structure and hypsodonty ( Bouvrain 1994a: 186) indicate close affinity with the Akkaşdagwı form.

A lot of words have been spent on the relationships of Pachytragus to the recent representatives of Caprini and/or Hippotragini ( Gentry 1971, 2000; Bosscha-Erdbrink 1988). Among other characters, Gentry (1971: 279) emphasizes the importance of the size of the central incisor as distinguishing Eurasian from African antelopes. In a general scheme ( Gentry 1970, 1987) i1 is slightly larger than other incisors and canine in Bovini, Panthalops and Caprini , while a significantly large i1 (associated perhaps with a reduced i3 and c) characterizes Tragelaphini , Boselaphini , Hippotragini and Antilopini . Hitherto, the incisor morphology and size of Pachytragus was unknown but the Akkaşdagwı material provides the first evidence on this feature, indicating a relation of the type i1> i2 = i3 <c. Although relatively worn, the first incisor of the Akkaşdagwı Pachytragus is larger than i2, a character that is also attested by its larger root ( Fig. 21B ). In the restricted mandible sample of living Caprini I have examined, i1 is equal in size to i2 and i3. It is the same in several fossil forms related to Caprini (cf. Gentry 1970: pl. 9, fig. 6, pl. 14, fig. 3), while late Miocene Antilopini show a significantly larger i 1 in comparison to the rest incisors and the canine. Although the size difference between the Perivolaki i1 and i2 is not as sharp as that shown in Antilopini , it indicates closer relations to the “African” pattern than to the “Eurasian” one (cf. Gentry 1970: pl. 9, fig. 5). Thus, the case for Pachytragus being related to Caprini ( Gentry 2000) would be weakened.

Figures

FIG. 18. — Pachytragus crassicornis Schlosser, 1904 from Akkaşdağı, skull GOK-181+182, lateral view. Scale bar: 5 cm.

FIG. 19. — Pachytragus crassicornis Schlosser, 1904 from Akkaşdağı, skull GOK-181+182; A, ventral view; B, dorsal view. Scale bar: 5 cm.

FIG. 20. — Pachytragus crassicornis Schlosser, 1904 from Akkaşdağı, frontlet AK2-503; A, lateral view; B, frontal view. Scale bar: 5 cm.

FIG. 21. — Pachytragus crassicornis Schlosser, 1904 from Akkaşdağı; A, upper toothrow AK2-312, occlusal view; B, lower toothrow AK2-63, lateral view. Scale bar: 4 cm.

FIG. 22. — Pachytragus horn-core distribution of basal measurements; ■, P. crassicornis Schlosser, 1904, Akkaşdağı;, BMNH M3878, Maragha;, P.?crassicornis, KTA;, Pachytragus sp., Kınık;, Protoryx carolinea Forsyth-Major, 1891, Pikermi;