Prostrepsiceros rotundicornis (Weithofer, 1888)

Kostopoulos, Dimitris S., 2005, The Bovidae (Mammalia, Artiodactyla) from the late Miocene of Akkaşdağı, Turkey, Geodiversitas 27 (4), pp. 747-791 : 757-761

Prostrepsiceros rotundicornis (Weithofer, 1888)

MATERIAL EXAMINED. — Frontlet: AK6-64, AK5-641; horn-cores: AK2-75dex, AK3-70sin, AK2-73dex, AK2-74sin, AK3-68sin, AK3-69sin, AK4-189sin; part of frontlet: AK5-152; part of horn-core: AK6-135, AKB-28; P4-M3: AK3-220sin; P3-M3: AK5-51sin; M1-M3: AK6-72dex, AK2-45dex, AK4-195sin; p2- m3: AK7-102sin, AK2-459sin, AK5-618sin, AK5- 615sin, AK2-323dex, AK2-318dex; p3-m3: AK3-76sin, AK5-639sin, AK2-457sin, AK3-190dex; p4-m3: AK5-617sin, AK6-191sin; m1-m3: AK4- 200dex, AK5a-259dex, AK5a-207dex, AK2-458dex; p3-p4: AKA-6; m3: AK5-50sin, AKK-79; distal part of humerus: AK2-79; radius: AK2-326; metacarpal: AK2-474; distal part of tibia: AK14-20; astragal: AK7- 176; calcaneus: AK3-75; metatarsal: AK3-222, AK9- 309; phalanx I: AK2-79, AK5-252; phalanx II: AK5-373.

DESCRIPTION

Skull

Prostrepsiceros rotundicornis represents a medium sized antelope with moderately long horn-cores, relatively robust at their base ( Fig. 8 ; Appendix: Table 7). The width of the skull behind the horncores ranges between 65 and 68 mm (Appendix: Table 7). The interfrontal suture rises as a ridge and is visible ahead of the horn-cores. The frontals are not elevated between the horn-cores and appear slightly convex in lateral view ( Fig. 8A ). There are no internal sinuses in the frontals or reaching into the pedicles. In the postero-distal part of the medial side (around the pedicles) the frontals are significantly depressed. The supraorbital foramens are relatively large, situated in large and deep pits which extend forwards like depressions; their lateral border is higher than the medial one. The rather rounded orbits (anteroposterior axis 32-36 mm) are moderately project- ed with widely extended dorsal rim. The postcornual grooves are rounded and shallow. The pedicles are sub-rounded and short. Their contact with the horn-cores is sharp anteriorly but less developed posteriorly. The horn-cores are situated over the orbits, strongly tilted backwards (≈ 40° with the cranial roof) and slightly divergent (≈ 50-60°); their anteroproximal margin is placed above the anterior third of the orbital rim. They are closely situated at their bases and lyriform in frontal view. At about 5 cm above the base, the horn-cores curve moderately backwards, whereas they are re-curved upwards at their top. The horn-core’s cross-section is elliptical at the base (Appendix: Table 7) with strongly convex medial side and slightly convex lateral one. Their greater anteroposterior axis at this level forms an angle of about 50° with the sagittal plane. 7 cm above the base the cross-section becomes subsquarish with the greater axis parallel to the sagittal plane. In the uppermost part of the horn-cores the crosssection becomes sub-triangular. The horn-cores are about 230 (AK5-641) to 240 mm (AK6-64) long, normally (anticlockwise) and relatively tightly spiraled and slightly torsioned. Thin discontinuous furrows run along their surfaces. Two keels are present. The “anterior” one descends to the postero-medial side of the base, forming a complete gyre towards the apex. It is smooth in the lower part of the horn-core but becomes sharper in its upper half ( Figs 8 ; 9 ). A deep longitudinal furrow, starting 2-3 cm above the base, runs in parallel with this keel or even replaces it ( Figs 8 ; 9 ). Nevertheless, the presence and development of this furrow is variable: it is very deep in AK4-189, well expressed but less deep in AK6- 64, AK2-75, AKB-28, weak in AK2-73 and double in AK5-641 and AK3-70. The second keel descends over the anterior margin of the postcornual groove and also forms a complete gyre towards the top. In the lower 3/4 of the horn-core it is weak but becomes thin and spiky towards the uppermost part. Deep furrows associate with this keel in the proximo-lateral face of the horn-cores, while in some specimens a deep and narrow furrow follows the keel towards the middle of the horn-core’s height (AK3-70, AK5- 641). In two specimens (AKB-28 and AK4-189) the furrow is projected to the pedicle.

Hornless skull (AKB-97)

A badly preserved skull of a medium-sized antelope (AKB-97) is included into this species. The skull maintains just the braincase, the frontal region and part of the basioccipital. The total absence of horn-cores indicates a female individual. The cranial roof is strongly convex and the braincase more bulky than that of Gazella (AKB- 29). The frontals form an angle of about 115° with the cranial roof. The interfrontal suture is simple. The orbit is strongly projected laterally with wide dorsal orbital rim. The supraorbital foramen is small and there are no pits. The parietal crest is strong, starting just behind the dorsal orbital rim and directed posteriorly and upwards, where it gradually disappears. The occiput is short and wide, forming an angle of about 78° with the basal axis. The mastoid is large. The basioccipital is short and trapezoidal shaped. The posterior tuberosities are small and globular, forming a smooth crest, placed vertical to the sagittal plane. The anterior tuberosities, situated behind the small oval foramen, are smaller than the posterior ones and elongated-hilly shaped. A weak crest runs along the basioccipital groove. The auditory bulla is short and oblique comparatively to the sagittal plane (32°). The condyles are strong and distant. The foramen magnum is wide. The paroccipital process is situated more anteriorly than in Gazella (AKB-29) and projects laterally.

The morphological characters of the skull point to a representative of Prostrepsiceros ( Bouvrain 1982; Bouvrain F Thomas 1992), while the dimensions indicate a similar size category with the previously described frontlets.

Dentition

A few upper toothrows are known (Appendix: Table 8). The length M1-M3 varies between 39.1 and 42.5 mm whereas the upper premolar length is unknown. P3, 4 have strong paracone and parastyle. P4 is slightly asymmetrical and bears traces of a possible hypoconal islet. The upper molars have strong styles, angular protocone and wide hypocone. A small central islet is present. The metastyle of M3 is strong directed backwards.

The length p2-m3 ranges between 68.8 and 75.1 mm with short premolars comparatively to the molars (premolar/molar ratio: 6 2-7 1) (Appendix: Table 9). In p3 ( Fig. 10 ) the paraconid is independent from the larger parastylid until the middle of the crown’s height. The metaconid is extended posteriorly, fused quickly with the entoconid. The p4 is morphologically similar to p3 but with more rounded metaconid and stronger hypoconid. The lower molars bear a thin basal pillar and a smoothly developed goat fold ( Fig. 10 ). The third lobe of m3 is formed by a single tubercle and has a slightly concave lingual face.

Bovidae (Artiodactyla) from Akka s daw gı

Postcranials

The metapodials are elongated and slender (length of MtIII+IV = 203 mm, DTdia = 1 6 m m, r o b u s t i c i t y i n d e x: 7.9; l e n g t h o f MtIII+IV = 212.2 mm, DTdia = 16 mm, DTdistal = 26.2 mm, robusticity index: 7.5). The index “Length of metacarpal/Length of radius × 100” is 0.76 and the index “Length of metacarpal/Length of metatarsal × 100” about 0.95, indicating a fast runner.

COMPARISON

The general morphological characters of the available frontlets and horn-cores allot the medium sized antelope of Akkaşdagwı to Prostrepsiceros ( Gentry 1971; Bouvrain 1982; Bouvrain F Thomas 1992). Although late Miocene Prostrepsiceros is well known from several localities of the Greco-Iranian province, it is scarcely recognized in Turkey ( Şenyürek 1952; Ozansoy 1965; Tekkaya 1973b; Köhler 1987; Bouvrain F Thomas 1992; Gentry 2003). In my knowledge the Akkaşdagwı sample constitutes at present time the best known evidence of this genus in the country.

Prostrepsiceros vallesiensis Bouvrain, 1982 , known from the late Vallesian (MN 10) localities of Greece and Turkey ( Gentry 2003), differs from the Akkaşdagwı Prostrepsiceros in its significantly smaller size, lack of supraorbital pits, shorter, more slender and more tightly spiraled horncores with strong mediolateral compression and sharp keels, as well as, in the comparatively long- er basioccipital.

The Akkaşdagwı Prostrepsiceros also differs from P. syridisi Kostopoulos F Koufos, 1996 (fide Bouvrain F Heintz pers. comm.) from the latest Vallesian locality Nikiti-1, Greece (Bonis F Koufos 1999) in the longer premolar row (premolar/molar ratio = 62-71 in Akkaşdagwı versus 56-60 in NKT), the constricted interfrontal suture, the large supraorbital foramens into deep pits, the more robust horn-cores inserted more uprightly and situated more closely on the frontals with less developed keels, more rounded cross section and more medially descended anterior keel.

The type species of the genus, P. houtumschindleri (Rodler F Weithofer, 1890) , originally described from Maragha, Iran, differs from the Akkaşdagwı Prostrepsiceros in the feebler facio-cranial angle, the smaller supraorbital foramens and postcornual grooves, the wider separation of the horn-cores on the frontals, their stronger mediolateral compression ( Fig. 11 ) and tighter twist and in the presence of a vigorous posterior keel. Prostrepsiceros vinayaki ( Pilgrim, 1939) is a poorly known species. According to the available data from several localities ( Pilgrim 1939; Gentry 1999; Bouvrain F Heintz pers. comm.) it differs from the Akkaşdagwı Prostrepsiceros in the longer and slenderer horn-cores, which are more torsioned than spiraled and extremely compressed mediolaterally. The deep anterior furrow, the short pedicles, the close setting of the horn-cores at their base, the large supraorbital foramens into pits and the weak postcornual fossa observed in Akkaşdagwı Prostrepsiceros are also present in the large P. lybicus Lehmann F Thomas, 1987 from

, P. rotundicornis, Pikermi ; ◆, P. rotundicornis, RZO ;, P. rotundicornis, Gökdere ;, P. houtumschindleri (Rodler & Weithofer, 1890) , Maragha; +, P. fraasi ( Andree, 1926) , Maragha, Samos; ▲, P. zitteli Schlosser, 1904 type, Samos; ▲, P. axiosi Kostopoulos, 2004 , RZO, PXM. Abbreviations: DAP, anteroposterior diameter; DT, transverse diameter. Data from Gentry 1971; Watabe 1990; Bouvrain & Thomas 1992; and pers. data.

Sahabi, Libya, which, however, has significantly longer horn-cores, more compressed mediolaterally and less torsioned.

Prostrepsiceros zitteli Schlosser, 1904 is originally known from Samos and also described from Kavakdere, Turkey (Geraads F Güleç 1999; Kostopoulos 2004). It is slightly smaller than the Akkaşdagw ı form with feebler facio-cranial angle, absent interfrontal suture ahead of the horns, more laterally projected orbits, absent postcornual grooves, more widely separated horn-cores on the frontals, stronger anterior keel, tighter torsion and stronger distal curvature. Prostrepsiceros axiosi Kostopoulos, 2004 from Axios valley, Greece, is significantly larger than the Akkaşdagwı Prostrepsiceros ; its horn-cores are more widely spa- ced on the frontals, stronger curved backwards and torsioned, stronger keeled and more compressed anteroposteriorly ( Kostopoulos 2004).

Prostrepsiceros fraasi ( Andree, 1926) is originally described from Samos by a single frontlet. A similar form from Maragha was described under various names ( Mecquenem 1924; Andree 1926; Watabe 1990). Gentry (1971) and Solounias (1981) regarded the species as a synonym of P. rotundicornis from Pikermi, but Bouvrain (1982), Bouvrain F Thomas (1992), Gentry F Heizmann (1996) and Gentry et al. (1999) consider P. fraasi as a valid species. Recently, Bouvrain F Heintz (pers. comm.) suggest referring to the Maragha form under the name P. gaudryi Mecquenem, 1908 . P. fraasi (including the Maragha form) is somewhat larger than the Akkaşdagwı Prostrepsiceros ( Fig. 11 ) with similarly inclined face but without postcornual grooves, ridge-like frontoparietal suture, wider separated, more strongly diverged and less torsioned horn-cores with a vestigial anterior keel and no posterior one (Bouvrain F Thomas 1992; Gentry 1999; pers. obs.).

The Pikermi P. rotundicornis (Weithofer, 1888) is the more allied species to the Akkaşdagwı form, b o t h m o r p h o l o g i c a l l y a n d m e t r i c a l l y. T h e medium size, the moderately inclined face, the projected orbital margins, the constricted interfrontal suture in front of the pedicles, the large supraorbital foramens into pits, the robust horncores comparatively to the skull, inserted in the posterior part of the orbits, their close setting on the frontals, their weak anteroposterior compression, their moderate torsion and closed spiraling and the presence of a weak anterior keel descending anteromedially, which is sometimes accompanied by a longitudinal furrow (two of four specimens in BMNH) are common characters in both Pikermi and Akkaşdagwı forms. However, the Turkish Prostrepsiceros differs in the larger supraorbital foramens situated in deeper and wider depressions, the shallower postcornual grooves, the higher pedicles (especially on the lateral face), the weaker divergence and the persistence of keels instead of furrows.

Bouvrain (1982) also refers to P. rotundicornis , the large Prostrepsiceros from Ravin de Zouaves 5 (Axios valley). This form is known by two frontlets (RZO-223 and RZO-120, LGPUT) that look identical to those from Akkaşdagwı: both have a weak but visible posterior keel, descending to a postero-lateral insertion and strengthening upwards, large supraorbital foramens (however smaller in Akkaşdagwı) in wide depressions of the frontals, shallow postcornual grooves, lyriform pattern of the horn-core’s divergence, short pedicles, tending to disappear posteriorly, and strongly grooved baso-lateral surface. Similarly to the Akkaşdagwı form a weak longitudinal furrow associates the posterior keel of RZO- 223 in its proximal part, while an anterior furrow is also present but less developed. Finally, both forms have similar horn-core length and basal dimensions that appear to be slightly larger than those of the Pikermi population. Based on the cone impression of a horn-core, its robusticity could be expressed as the relation of the horn-core length [Ls measured along the anterior face, to the basal area [BA = π(D/2) 2 s, considered as a circle with diameter D equivalent to the mean diameter of the base. Thus, the Horn-core robusticity index, HcRI = BA/L ranges from 3.7 to 4.6 (n = 2) in Akkaşdagw ı Prostrepsiceros , being very close to the estimated values for the two RZO frontlets (3.5- 3.8) and slightly larger than those of Pikermi (3.3-3.4; n = 2).

Şenyürek (1952: figs 45-47) also mentioned two horn-cores from Gökdere ascribed to P. rotundicornis . They are slightly smaller than the studied form and closer to the Pikermi one, but similarly to Akkaşdagwı, they seem to bear a well developed posterior keel and an anterior furrow. Although Bouvrain (1994a) mentioned the absence of Prostrepsiceros in Kemiklitepe ( Turkey), the original comparison of the material showed that the specimen KTA-189 (distal part of a left horncore) included in x Oioceros wegneri by Bouvrain (1994a) rather corresponds to Prostrepsiceros , being similar to that from Akkaşdagwı. The specimen bears a deep anterior furrow like the Akkaşdagwı form and an even more marked posterior keel.

I certainly regard the Akkaşdagw ı and RZO Prostrepsiceros as conspecific. The Gökdere form seems to be very close to this group, which also occured in Kemiklitepe A-B. The relations with the Pikermi P. rotundicornis are obviously strong, and the small differences cannot be considered as overpassing intraspecific variation.

Figures

FIG. 8. — Prostrepsiceros rotundicornis (Weithofer, 1888) from Akkaşdağı, frontlet AK5-641; A, lateral view; B, frontal view. Scale bar: 5 cm.

FIG. 9. — Prostrepsiceros rotundicornis (Weithofer, 1888) from Akkaşdağı, horn-core AK4-189, antero-internal view. Scale bar: 5 cm.

FIG. 10. — Prostrepsiceros rotundicornis (Weithofer, 1888) from Akkaşdağı, mandible AK2-323, occlusal view. Scale bar: 2 cm.

FIG. 11. — Prostrepsiceros horn-core distribution of basal measurements. ■, P. rotundicornis (Weithofer, 1888), Akkaşdağı;