Lophuromys sikapusi ( Temminck, 1853 )

Denys, Christiane, Missoup, Alain Didier, Nicolas, Violaine, Sylla, Morlaye, Douno, Mory, Kadjo, Blaise, Lalis, Aude & Monadjem, Ara, 2025, Annotated checklist of rodents from a biodiversity hotspot, Mount Nimba (West Africa), Zoosystema 47 (27), pp. 617-689 : 649

Lophuromys sikapusi ( Temminck, 1853)

Mus sikapusi Temminck, 1853: 160 .

Lasiomys afer Peters, 1866: 409 .

Lophuromys afer – Peters 1874: 234.

Lophuromys sikapusi – Allen 1939: 395.

REMARKS

Most of the Lophuromys captured display the typical red brown pelage, small size, and short tail, which characterizes the sikapusi complex, but some specimens collected at 1600 m altitude in the Mare d’hivernage showed a slightly darker pelage than specimens living at lower altitudes. Such colour variability was also noticed by Roche (1971) for the Seredou ( Guinea) Lophuromys series. Three females and six males from three localities and two altitudes (600 and 1200 m) yielded the same karyotype of 2 N = 66, NFa=76, which differs from known L. sikapusi of Côte d’Ivoire (2 N=60, 64; NF =70-76, Matthey 1958; Gautun et al. 1986). Previous work in western Guinea indicated that L. sikapusi was characterized by a 2N= 66, NFa= 74 ( Denys et al. 2009). Some molecular analyses ( Missoup 2010, pers comm.) confirm that all the Nimba specimens belong to the L. sikapusi clade, but also that a high genetic variability with at least two subclades is present on Mount Nimba. This robust rat harbors short legs, a short tail and short ears and the tail is uniformely naked and black. All newly collected specimens from Guinean and Liberian Nimba fit well in size and proportions with those previously collected despite a wide variability ( Table 7 ).

The skull of Lophuromys is relatively large and somewhat triangular in outline. The nasal bone is long and narrow, the IOC very large with sometimes visible bumps. The zygomatic arches are close to the skull and low. The braincase is wide and long. The incisors are either orthodont or proodont. In ventral view the incisive foramina are long and wide and stop between the dental rows at the level of the upper M 1 t 4 cusp. The dental rows are parallel, and the palate is short ending in between the upper M3. The pterygoid fossae are long and narrow, the tympanic bullae are small, the mastoid part of the bullae is slightly inflated. The mandible is low and long and displays a large variability in size. The lower incisors are long and poorly curved. There is a large size variability but both newly collected specimens from Guinea and Liberia display same range of measurements with slightly smaller mean values in the Guinean populations ( Table 8 ). On the molars, the cusps are high and rounded. On the upper M1, the t1 is relatively well individualized and posterior to the t2- t3. The t3 is not well individualized and its posterior border is oblique with a little crest. Discrete stephanodont crests are visible on some upper molars as well as some supplementary cingular cusplets. The M3 is small and reduced to two more or less oblique laminae of cusps. On the lower molar rows, the prelobe is fused to the first chevron by a longitudinal crest and the two cusps of the prelobe are separated by a small valley where in some cases a tmA develops. There is a large posterior cingulum on m1-2 and a small antero-labial cusp on m2. The m3 is small with two rows of cusps. An important variability of the cusp disposition and of the size of molar rows is observed in the Nimba populations.