Prostrepsiceros vallesiensis Bouvrain, 1982

Kostopoulos, Dimitris S., 2009, Contribution to the systematics and phylogeny of Bouvrain, 1982 (Mammalia, Bovidae), Geodiversitas 31 (4), pp. 879-891 : 880-884

publication ID	https://doi.org/ 10.5252/g2009n4a879
persistent identifier	https://treatment.plazi.org/id/03D687CB-6737-FFA1-E9E8-FE177EBFFDC0
treatment provided by	Marcus
scientific name	Prostrepsiceros vallesiensis Bouvrain, 1982
status

Treatment

HOLOTYPE. — Cranium RPl-234 illustrated by Bouvrain (1982: figs 2, 3); Fig. 1. View FIG

TYPE LOCALITY. — Ravin de la Pluie, Axios valley, Greece.

NEW REFERRED MATERIAL. — Frontlet, RPl-115n; horncore, RPl-114n; Fig. 2. View FIG

DEPOSIT. — Laboratory of Geology & Paleontology, University of Thessaloniki.

EMENDED DIAGNOSIS. — Prostrepsiceros of small size; females horned; basioccipital long and narrow with strong medial groove; nasal bones short, ending anteriorly at a single point; face slightly inclined to the opisthocranium; frontals very weakly inflated between the horn-cores in male individuals; supraorbital foramina small, round to pear-shaped and not sunken into pits; postcornual groove very shallow to almost absent; pedicels very short antero-laterally; horn-cores moderate in size compared to the skull; medio-lateral compression strong, increasing rapidly from the base to the top in females; moderate to strong postero-lateral and antero-medial keels; horn-cores weakly twisted (tighter in females) and very closely spiralled (more openly in females); primitive lower premolars; advanced hypsodonty; long, slender limbs.

OTHER OCCURENCES. — Middle Sinap, locality 40, Turkey.

AGE. — Late Vallesian (MN10).

DESCRIPTION

RPl-114n ( Fig. 2C View FIG )

Proximal part of a right horn-core with part of the frontal bone. The APD at the base is = 31mm and the TD at the base is 23.3mm. The preserved length is about 120 mm but the cross-section at the top level indicates a longer horn-core, which probably attains 200 mm. The pedicel is very short posteriorly and not distinct from the horn-core at the medial and antero-lateral sides. Thin discontinuous grooves run along the horn-core surface. The basal cross-section is oval to elliptical and becomes almost semicircular towards the distal tip. The zone of maximum transverse thickness at the base is short and lies anteriorly. Medio-lateral compression is strong (75%) and increases further from the base to the top. The lateral face is slightly convex at the base, becoming flat or even concave upwards. The medial face is strongly convex.Two keels are present; a rather sharp anterior keel descends antero-medially, whereas a blunt posterior keel, probably affected by rolling, descends postero-laterally, giving rise to an almost flat postero-medial basal surface. Spiralling is close with coils weakly deviating from the torsion axis of the horn-core.Torsion is rather loose; at 10 cm from the base the antero-medial keel takes a lateral position, whereas the posterior one is shifted postero-medially (~1/2 of a complete coil).

RPl-115n ( Fig. 2A, B, D View FIG )

Frontlet with proximal part of horn-cores. The back of the face slopes gently on the cranial roof. The mid-frontal suture is slightly raised in front of the pedicels. The frontals appear slightly thickened between the horn-cores. The supraorbital foramina are small, rounded and not sunken into pits; they are placed rather laterally compared to the descending point of the anterior keel. There are no sinuses in the frontals. The pedicel is observable only in the antero-lateral side of the horn-core base, while a smooth ridge occurs in its antero-medial face. The horn-cores are rather closely set on the cranial roof; the internal distance between the horn-core bases is 17.7 mm and the external one about 70.5 mm. The external distance between the supraorbital foramina is 35.3 mm. The APD at the base of the right horncore is about 30 mm and the TD is 20.4 mm. The horn-cores are moderately divergent (~40°). The major axis of the horn-core base (APD) forms an angle of about 45° with the sagittal plane of the skull. The horn-cores are strongly tilted backwards; their angle with the preserved part of cranial roof is about 35°. They show a strong posterior keel descending postero-laterally and a blunt anterior keel descending antero-medially; the latter seems however, to be post-mortem weathered. Their torsion and spiralling are similar to those of the specimen RPl- 114n.

REMARKS

According to the original diagnosis of Prostrepsiceros vallesiensis given by Bouvrain (1982: 118) this species is characterized as: “ Prostrepsiceros of small size; horn-cores strongly compressed medio-laterally and small relatively to the skull; nasal bones short, ending anteriorly at a single point; face slightly inclined to the braincase; supraorbital foramina small and not sunken into pits” (translated from French). As Gentry (2003) points out, the name of the species was spelled vallesienis on the page where it was formally founded ( Bouvrain 1982: 118), but it appears almost everywhere else as vallesiensis , which should be considered as the valid name (ICZN Art. 32.5).

As noted by Bouvrain (1982), the holotype of P. vallesiensis ( Fig. 1 View FIG ) belongs to a young adult individual; the M3 is fully erupted but in the first stage of wear. Although the cranium represents a pre-mature stage of ontogenetic development, its horn-core morphology and size should correspond to a final stage. In similar sized extant antilopines (e.g., Gazella dorcas ) a fully erupted and unworn M3 is usually associated with completely developed horn-cores.

The two new specimens RPl-114n and RPl-115n share in common with the holotype cranium RPl- 234 of P. vallesiensis the weak inclination of the face on the cranial roof, the small and rounded supraorbital foramina without surrounding pits, and the general pattern of the horn-core morphology with close spiralling and loose torsion, strong medio-lateral compression and two more or less equally developed keels ( Fig. 2 View FIG ). There is, therefore, no doubt that both new specimens belong to P. vallesiensis . Their absolute dimensions are, however, significantly larger (at about 10-15% in skull measures and 30-40% in horn-core dimensions; Fig. 3 View FIG ) than those of the holotype, indicating important intraspecific variability. Equivalent size differences are quite commonly displayed in sexually-dimorphic living and extinct bovids of open landscapes. Other morphological features come across as sexual dimorphism as well: even partly destroyed, the frontals of the holotype do not show the slight thickening between the horn bases seen in RPl-115n, whereas the horn-cores of RPl-234 are comparatively more widely spaced at their bases than those of RPl-115n ( Figs 1 View FIG , 2 View FIG ). Both features are usually indicative of horned female bovids in contrast to their male counterparts.

Judging from the comparison it is, consequently, suggested that the holotype cranium of P. vallesiensis should be ascribed to a female individual. According to this concept, the males of P. vallesiensis are larger, with thickened interfrontal region and more closely set horn-cores on the cranial roof, more loosely twisted and less coiled with a more convex medial face, elliptical to semicircular cross-section (instead of elliptical to spindle-shaped in females) and weaker medio-lateral compression towards the distal tips. The TD*100/APD index at the base is 72 in the type specimen (RPl-234) vs. 68 in RPl-115n and 75 in RPl- 114n. At 4 cm above the base, however, the same index becomes 49.5 in the type specimen vs. 69.6 and 69.2 for the other two, indicating that the females have more compressed and faster tapering horn-cores than the males. The diagnosis of P. vallesiensis is, consequently, modified according to the new data, while the remaining cranial, postcranial and dental features follow Bouvrain (1982) and Bouvrain & Bonis (1985).

Outside the Axios valley, forms referred to P. vallesiensis have been recently described from Turkey. The specimen Loc. 40 89.457 from the MN 10 of Middle Sinap is described and figured by Gentry (2003: 350, fig.15.12) as P. aff. vallesiensis because it is similar to the type of this species but larger, less twisted, with less prominent postero-lateral keel and more convex medial surface. As already mentioned, these differences fall into the observed intraspecific variation seen in the type locality and they are interpreted as sexual dimorphism. The Turkish specimen shows great morphological and

B, D, frontlet RPl115n; C, right horn-core RPl114n; A, anterior;

dimensional similarity to the male specimen RPl- 114n ( Fig. 3 View FIG ) and it could therefore be fully attributed to P.vallesiensis ; the compatible geological age of both forms further supports such a decision.

Gentry (2003) also referred to Prostrepsiceros sp. a few additional specimens from the MN 9 of Middle Sinap ( Fig. 3 View FIG ), mentioning affinities to P. vallesiensis . Although the described specimens are collected from different sites, they show most of the characters credited to P. vallesiensis from RPl. As Gentry (2003) points out, the most important differences of the Loc. 91 specimens from P. vallesiensis are the weaker spiralling and the narrower dorsal orbital rims.