The highland small rice rat is a small rodent recorded in Andean páramo. An Ecuadorian study found lineage differences between northern and southern samples and noted that the northern group may be a separate species.
Southern M. altissimus sensu stricto specimens had dorsal hairs with gray bases, yellow-brown middle bands, and black tips; belly hairs had gray bases and cream tips. The northern sample may represent another lineage.
In Ecuador, the study recorded refuges in shrubs, soil cavities, fallen logs, and rock walls, and found animals in páramo grassland and around Polylepis forest.
An extinction-risk assessment has not been added yet.