Oenomys hypoxanthus ornatus Rosevear, 1969

(Tables 7; 8)

Oenomys hypoxanthus ornatus Rosevear, 1969: 344.

REMARKS

Specimens belonging to this taxon were reported by Heim de Balsac & Lamotte (1958) for the first time as O. hypoxanthus ornatus. Rosevear (1969), followed by Tranier & Gautun (1979) who described its distinctive morphological and cytogenetical characteristics, elevated it to species rank. Oenomys ornatus is endemic to West Africa and has been recorded in Côte d’Ivoire, Liberia, Guinea, Ghana and Sierra Leone. Misonne & Verschuren (1976) collected four supplementary specimens on the Liberian side of Mount Nimba. We were unable to capture new specimens during our recent surveys.

A single MNHN specimen collected by Lamotte had external standard measurements (Table 7). It is characterized by reddish pelage around the nose, a grey-brown dorsal pelage with reddish flanks, hindfeet and back, and a white belly. A comparison with O. ornatus specimens from Seredou (Guinea) and the two karyotyped specimens from Côte d’Ivoire shows their great similarities in size and morphology but some differences with the holotype. The Nimba specimen is one of the largest compared to other Guinean representatives. The skull of the Nimba Oenomys is robust with a large rostrum (Table 8). On the ventral side the infra-orbital foramen just stops at the level of the first root of the upper M1/. The incisive foramina are broad in front and strongly narrower behind. The two upper molar rows are large and nearly parallel, the palate is very narrow. The tympanic bullae are moderately inflated and represent about 15% of the greatest length of the skull. In size, the Nimba specimen is larger than the holotype of O. ornatus but fits within variability of the karyotyped specimens from Côte d’Ivoire and from Seredou (Guinea). The molars of the Nimba specimen are relatively worn (stage 4) but they display a typical stephanodont pattern with crests developed longitudinally for each cusp of the upper molars. On the M1 and the M2 the central row of the cusps is large and round, there are some supplementary cusplets and the t9 is small but present. The upper M3/ is long and its first lobe has two cusps related to the second lobe on the labial side. Cusps are alternate on the lower m1, there is a tmA and a cv5 on the m1 and the posterior cingulum is small.