It was separated from the genus Marmosa in 1989, and has since had the genera Cryptonanus, Chacodelphys, and Hyladelphys removed from it.

[citation needed] Another general characteristic that mouse opossum have are mammary glands.

The different regions that Gracilinanus species can be found are Peru,[9][10] Bolivia,[9][10][11] Brazil,[10][12][13][14] Paraguay,[10] and Venezuela.

[6] G. agilis and G. microtarsus are the only two species that have been found in the central, south, and southeastern parts of Brazil.

[15] The production of sugar cane and fruits, along with deforestation, is thought to be a reason why the newer species, G. ignitus, has been harder to find.

[10][11][12][14] However, it has also been reported that these species are on the critically endangered list because they are only known in two general areas where their habitat has been found to be taking a decline.

[3] The species G. microtarsus has a diet that includes insects, spiders, fruits, termites, beetles and ants.

[3][10][15] For those that do not have a pouch, the young are only attached to the nipples for a short time period and are left in their nests early on in their life.

[6] The species in this genus are known to climb a lot and dig holes in trees or the ground.