First described in 2010, it is placed in the genus Brachytarsomys together with two larger living species, which may differ in some details of molar morphology.

The presence of B. mahajambaensis, a rare element in the local rodent fauna, suggests that the region was previously more humid.

[4] Brachytarsomys is classified in the exclusively Madagascan subfamily Nesomyinae of the family Nesomyidae, which includes various African rodents.

The metacone is broadly connected to another labial cusp behind it, referred to as the "post-hypocone", which it is expected to fuse to with increasing wear.

[3] The anterolingual cingulum on the M2, a crest on the front lingual corner, is absent or very small; it is well-developed in B. albicauda.

[3] Brachytarsomys is a rare element of the rodent fauna, which is dominated by multiple species of Eliurus and Macrotarsomys.

[7] Modern Brachytarsomys are large rats that live in trees and eat fruits at the middle to high altitudes.

The modern, dry environment in northwestern Madagascar is decidedly inhospitable to these animals, and they no longer occur there; the former presence of B. mahajambaensis could indicate that the region was more humid in the past.