Samotragus crassicornis Sickenberg, 1936

Kostopoulos, Dimitris S., 2014, Taxonomic re-assessment and phylogenetic relationships of Miocene homonymously spiral-horned antelopes, Acta Palaeontologica Polonica 59 (1), pp. 9-29 : 15-17

Samotragus crassicornis Sickenberg, 1936

Fig. 4.

Holotype: Frontlet, NHMW A4787 ( Sickenberg 1936: pl. 3: 1, 2).

Type locality: Samos, Greece (unknown level).

Type horizon: Judging from the quality and color of fossilization of the holotype in Vienna, it seems likely that it came from the Main Bone Beds Member of the Mytilinii Formation, Samos , indicating a middle Turolian (Late Miocene) age ( Kostopoulos et al. 2003) .

Material.—Frontlets, NHMW A4787, AMNH 22639 (cast); partial skulls SMF M1965, AMNH 104791.

Emended diagnosis.— Samotragus of medium size; braincase moderately long and narrow, with weak temporal lines; frontals moderately elevated between the horncores and hollowed out anteriorly; occipital facing bilaterally; horncores uprightly inserted above the orbits, strongly curved posteriorly at halfway point, and abruptly tapering; horncores very close together at the base, closely converging at mid−height, and strongly diverging laterally in their distal part; horncore cross section squared at the base ( Fig. 1 ) with a proximally flattened posterior surface, changing to roughly triangular at mid−height; proximal part of horncores bearing a deep lateral furrow and showing pronounced “exostosis”.

Remarks.—Apart from the holotype, two additional specimens from Samos have been referred to this species ( Solounias 1981): a frontlet from the Korff Collection, Hanaw, Germany (cast AMNH 22639); and a partial skull (SMF M1965; Fig. 4), on which the revised diagnosis of the species is mainly based. Gentry and Heizmann (1996) and Gentry et al. (1999) suggested that Samotragus crassicornis from Samos may represent males of Oioceros rothii from Pikermi (allowing synonymy at the generic level), without providing strong evidence. However, horncore size variation within Oioceros rothii supports the presence of horned females like in O. atropatenes at Maragheh, Iran, whereas some hornless specimens from Samos (e.g., AMNH 104791) may represent females of S. crassicornis , given their morphological compatibility with both male skulls of S. crassicornis and females of S. praecursor Bouvrain and Bonis, 1985 from the Axios Valley, Greece.

Geographic and stratigraphic range.—?Middle Turolian (Late Miocene) of Greece.

Samotragus praecursor Bouvrain and Bonis, 1985 Fig. 5A, B, E .

Holotype: Skull, LGPUT RPl−480 ( Bouvrain and Bonis 1985: figs. 1, 3; Fig. 5B ).

Type locality: Ravin de la Pluie, Axios Valley, Greece ( RP 1).

http://dx.doi.org/10.4202/app.2011.0013

Type horizon: Late Vallesian (magnetostratigraphically calibrated at 9.3 Ma; Sen et al. 2000), Late Miocene.

Material.—Horned skulls and frontlets, LGPUT RPl−480, RPl−38, RPl−263, RPl−264, RPl−280, RPl−394, RPl−349, RPl−481, RPl−105n, RPl−109n, RPl−111n, RPl−112n; isolated horncores, LGPUT RPl−37; RPl−350, RPl−385, RPl−108n, RPl−110n; hornless skulls, LGPUT RPl−211, RPl−479, RPl− 482; dental and postcranial material as in Bouvrain and

Bonis (1985). Emended diagnosis (modified from Bouvrain and Bonis

1985).—Small−sized Samotragus ; females hornless; opithocranium relatively short and box−like, with a rough dorsal surface around the fronto−parietal suture; supraorbital pits located close to the bases of the pedicles; face shallow and rather short, and moderately inclined compared to the braincase; nasals flat and rather short, roofing a shallow narial opening; contact between praemaxillae and nasals short; ethmoidal fissure very narrow or closed; choanae opening posterior to M3 and the lateral indendations of the palate; occiput moderately high and square−shaped, facing posteriorly; paroccipital processes strong and bearing posterior keels; foramen ovale large; horncores inclined more posteriorly than in S. crassicornis ; premolars moderately short compared to the molars; postcranials slender.

Remarks.—Several unpublished specimens of S. praecursor have been unearthed from its type locality during the past decade. Most of them fall well within the limits of the size and morphological variation defined by Bouvrain and Bonis (1985). One almost complete skull ( LGPUT RP1−105n; Fig. 5A ) helps, however, to clarify some previously unknown or badly defined cranial details, as included in the species diagnosis provided here.

Geographic and stratigraphic range.—Late Vallesian (Late Miocene) of Greece.

Samotragus cf. praecursor Bouvrain and Bonis, 1985 Fig. 5C, D .

Material.—Frontlet ( LGPUT RZ1−10), left horncore ( LGPUT RZ1−12), left juvenile horncore ( LGPUT RZ1−11), distal part of tibia, calcaneum, and astragalus ( LGPUT RZ1− 68), distal part of humerus, radius, and metacarpal III+IV ( LGPUT RZ1−69), proximal part of humerus ( LGPUT RZ1− 70), distal part of humerus, metacarpal III+IV, and proximal phalanges ( LGPUT RZ1−71), metacarpal III+IV and phalanges ( LGPUT RZ1−72), femur, tibia, metatarsal III+IV, and phalanges ( LGPUT RZ1−73). All specimens come from the locality of Ravin de Zouaves 1 ( RZ 1) in the Axios Valley of northern Greece, which provided a limited number of fossils. The locality is usually considered to be isochronous with Ravin de la Pluie (RPl; late Vallesian, MN10), the type locality of Samotragus praecursor . Nevertheless, the presence of Ouzocerus Bouvrain and Bonis, 1986 and the absence of Prostrepsiceros Major, 1891 from this site may be indicative of a slightly older age, probably closer to the age of the locality of Xirochori (Axios Valley, Greece), dated to 9.6 Ma ( Sen et al. 2000).

Description.—The Samotragus from RZ 1 is known from a frontlet, two isolated horncores and several postcranials, all of them so far undescribed ( Bouvrain and Bonis 1985, 1986). The RZ 1 horncores closely resemble those of S. praecursor from RPl (similar position above the orbits, similar degree of torsion; compare Fig. 5C, D with Fig. 5E ). However, the taxon from RZ 1 differs from S. praecursor in its smaller (about a quarter shorter and 15% thinner in absolute basal dimensions) and more gradually tapering horncores ( Fig. 5C, D ), as well as the presence of a less well−defined lateral furrow restricted to the laterobasal part of the horncores, the presence of a moderately developed anterior keel descending anteromedially and becoming stronger towards the apices ( Fig. 5C 1, D 1 ), the weaker posterior curvature of the horncores in lateral profile, the dorsal (instead of lateral) deflection of the distal portions of the horncores, the presence of wide and moderately deep postcornual fossae, less elevated frontals between the horncores, smaller supraorbital foramina located closer to the horncore bases, and an anteriorly notched fronto−parietal suture (Y−shaped as in S. crassicornis , and unlike the T−shape of S. praecursor ). The available postcranials from RZ 1 do not, however, differ from those of S. praecursor .

Remarks.—Although poorly documented, the RZ 1 Samotragus differs from S. praecursor in terms of both its horncore size and morphology, casting doubt on its previous taxonomic assignment ( Bouvrain and Bonis 1985, 1986). Several features of the RZ 1 taxon seem less derived than in the material from RPl, whereas others, such as the anterior keel and the straight axis of the horncore, show a residual occurance within the RPl polulation (e.g., a blunt anterior keel is present in the young male individual LGPUT RPl−109n, whereas LGPUT RPl−37 exhibits a straight horncore axis; Fig. 5E ). This may suggest a transition from the RZ 1 to the RPl morphotype.

Figures

Fig. 1. Box−plots of the horncore basal compression index (i.e., TD*100/ ADP) for several species and genera of Oiocerina, showing the medial (horizontal line inside the boxes), the 25–75% quartiles (gray boxes) and the minimum and maximum range of values (short horizontal lines). NKT−1, Nikiti−1; RZ1, Ravin des Zouaves 1.

Fig. 5. Oiocerin antelope Samotragus from Northern Greece. A, B, E. Samotragus praecursor Bouvrain and Bonis, 1985 from Ravin de la Pluie (RPl), Axios Valley, late Vallesian (Late Miocene). A. LGPUT RPl−105n, cranium in dorsal (A1) and lateral (A2) views. B. LGPUT RPl−480, holotype cranium in lateral view. E. LGPUT RPl−37, left horncore in lateral view. C, D. Samotragus cf. praecursor Bouvrain and Bonis, 1985 from Ravin des Zouaves 1 (RZ1), Axios Valley, late Vallesian (Late Miocene). C. LGPUT RZ1−11, left horncore in anterior (C1) and lateral (C2) views. D. LGPUT RZ1−17 left horncore in anterior (D1) and lateral (D2) views.