These species live in a wide variety of habitats, ranging from dry deciduous forests to rainforests, and run quadrupedally across branches.

Their diet consists primarily of tree gum and other exudates, though they may obtain some of their protein and nitrogen by hunting small arthropods later at night.

[6][7] The holotype is thought to be MNHN 1834-136, a female specimen taken from Madagascar by French naturalist Jules Goudot.

In the early 1930s, Ernst Schwarz, Guillaume Grandidier, and others resurrected the name, citing characteristics that were intermediate between Cheirogaleus and Microcebus.

[12] Until the late 20th century, there was only one recognized species of fork-marked lemur,[6] although size and coloration differences had been noted previously.

[6][13] In 2001, Groves elevated all four subspecies to species status[6][14] based on noticeable color, size, and body proportion differences between the fragmented populations.

Although Tattersall disagreed with this promotion, citing inadequate information for the decision,[15] the arrangement is generally accepted.

If shown to be a new species, they plan to name it after Fanamby, a key conservation organization working in that protected forest.

In 1904, Theodore Sherman Palmer attempted to document the etymologies of all mammalian taxa, but could not definitively explain the origins of the generic name Phaner, noting only that it derived from the Greek φανερός (phaneros) meaning "visible, evident".

Following some initial speculation, a search of the general literature published around 1870 revealed the source: the British comedy The Palace of Truth by W. S. Gilbert, which premiered in London on 19 November 1870, nearly one and a half weeks prior to the date written on the preface of Gray's manuscript (also published in London).

The comedy featured characters bearing three names: King Phanor (sic), Mirza, and Azema.

[19] A study in 2009 of seven mitochondrial genes (mtDNA) and three nuclear genes grouped fork-marked lemurs with sportive lemurs (family Lepilemuridae), offering a host of explanations, such as a possible hybridization (introgression) following the initial split between the families.

[25][26] Of the mostly small, nocturnal lemurs in family Cheirogaleidae, the genus Phaner contains some of the largest species, along with Cheirogaleus.

[30] Males have a scent gland on the middle of their throat,[27] which is approximately 20 mm (0.79 in) wide and pink in color.

[6][30] Their procumbent (forward-facing) lemuriform toothcomb (formed by the lower incisors and canines) is long[32] and more compressed, with significantly reduced interdental spaces to minimize the accumulation of gum between the teeth.

[33] The genus is distinguished from other cheirogaleids by the toothrows on its maxilla (upper jaw), which are parallel and do not converge towards the front of the mouth.

[14] The fork-marked lemur dental formula is 2.1.3.32.1.3.3 × 2 = 36; on each side of the mouth, top and bottom, there are two incisors, one canine, three premolars, and three molars—a total of 36 teeth.

[35] The next upper premolar (P3) is very small,[14] with a single, pointed cusp that contacts the lingual cingulum (a crest or ridge on the tongue side), which circles the base of the tooth.

[6][30] Their habitat ranges from dry deciduous forests on the western coast of the island to rainforest in the east.

[6] On average, males make approximately 30 loud calls per hour,[37][43] and are most vocal at dusk and dawn.

[49] Males and females have been seen sleeping and foraging together as monogamous pairs, although polygamy and solitary behavior has also been observed.

[50] At Kirindy Forest, pairs were observed staying together for multiple seasons, though they were only seen foraging alone, with most interactions resulting from conflicts over feeding sites.

[6][54] Their diet consists mainly of gum from trees in the genus Terminalia (known locally as "Talinala"),[6][42][55] which are often parasitized by beetle larvae that burrow beneath the bark.

[6][32] They have also been documented eating gums from Commiphora species and Colvillea racemosa, bud exudates from Zanthoxylum tsihanimposa, sap from baobab trees (Adansonia species),[32] nectar from Crateva greveana flowers, the sugary excretions from bugs (family Machaerotidae) which feed on trees of the genus Rhopalocarpus,[6][32][44] and very small amounts of fruit.

[44] Although fork-marked lemurs have widely varied forest habitat, gum and other plant exudates of other species are likely to dominate their diet.

Insects are captured by rapidly grasping them with the hands, a stereotypic behavior seen in other members of their family, as well as galagos.

In western Madagascar, interspecific competition is reduced by restricting activity to specific levels of the canopy, such as using only the highest sleeping sites at least 8 m (26 ft) above the ground.

[42] Studies of P. pallescens at Kirindy Forest found up to a 20% drop in body mass during the dry season despite no changes in exudate production, indicating flowers and insects have a significant impact on the species' health.

[43] In one case, a family of fork-marked lemurs exhibited mobbing behavior when they encountered a Malagasy tree boa.

[57][58][59][60] Before this assessment, it was assumed that their population was in decline due to habitat destruction for the creation of pasture and agriculture.