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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.
REFERENCES
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.
If I see it right, the animal on the photo has elongated fingers! I had got the impression that the hands of gliding animals were all of normal size, and that elongated fingers only occurred in bats. If this one has elongated fingers, that would give a good example of an intermediate stage that could be applied to bat evolution. Can thai Anomalurs raise its arms over its shoulder, to actually flap?
ReplyDeleteIf you look at the second photo, you can see that the hands aren't integrated into the glinding membrane in anomalurids. The long finger-like structure visible in the top photo is the cartilaginous support rod, not a finger.
ReplyDeleteI don't know if any living mammals have long fingers as part of a gliding membrane (other than bats, of course), but they do occur in gliding frogs.
Gerdien: as Christopher said, anomalurid fingers are of "normal" length. Animal Diversity Web has a drawing of a gliding Anomalurus pelii (that site has similar pictures of a few other anomalurid species too). You can probably see the support rods attached at the elbows in the picture.
ReplyDeleteColugos have the fingers integrated into the membrane, as can be seen in this picture:
ReplyDeletehttp://i.livescience.com/images/071031-colugos1-02.jpg
The fingers aren't very long, though.