The "scaly-tailed squirrels" of the family Anomaluridae are seven species in three genera of arboreal rodents found in western and central Africa. Like pretty much everything from western and central Africa, they're somewhat enigmatic. Relationships between anomalures and other rodents have long been debated; it seems likely that their closest relative is the springhaas Pedetes capensis, another African endemic (Blanga-Kanfi et al., 2009), but the relationship is not an overly close one, nor can we be really confident where the springhaas-anomalure clade sits in turn. One thing we can be reasonably sure of is that anomalures are not closely related to squirrels (despite the common name).
The names "scaly-tailed squirrel" and "Anomaluridae" (i.e. "strange tail") both refer to the double-row of keeled scales under the base of the tail, visible in the photo above. These scales are used to grip the tree on which the animal is climbing, and also as accessory landing gear in the two gliding genera, Anomalurus and Idiurus (Nowak, 1999). The monotypic third genus, Zenkerella insignis, lacks a gliding membrane (patagium). Idiurus and Zenkerella are currently regarded as more closely related than either is to Anomalurus, but this relationship does not seem to have been formally tested phylogenetically. In the two gliding genera, an elongate cartilaginous process extends from the elbow to support the patagium; similar processes have been evolved by other gliding mammals (Johnson-Murray, 1987), but anomalurids are remarkable in just how much it has been developed.
Anomalurus pelii is the largest of the anomalures, up to two kilograms in weight, and is found from Liberia to the Ivory Coast. The individual in the photo above is the Liberian subspecies A. pelii auzembergeri which differs from other subspecies in lacking bright white patches on the head and along the margins of the patagium, as seen in the photo below from here.
Blanga-Kanfi, S., H. Miranda, O. Penn, T. Pupko, R. W. DeBry & D. Huchon. 2009. Rodent phylogeny revised: analysis of six nuclear genes from all major rodent clades. BMC Evolutionary Biology 9: 71.
Johnson-Murray, J. L. 1987. The comparative myology of the gliding membranes of Acrobates, Petauroides and Petaurus contrasted with the cutaneous myology of Hemibelideus and Pseudocheirus (Marsupialia, Phalangeridae) and with selected gliding Rodentia (Sciuridae and Anomaluridae). Australian Journal of Zoology 35 (2): 101-113.
Nowak, R. M. 1999. Walker's Mammals of the World 6th ed., vol. 1. Johns Hopkins University Press.