The giant mouse lemurs are members of the strepsirrhine primate genus Mirza. Two species have been formally described; the northern giant mouse lemur (Mirza zaza) and Coquerel's giant mouse lemur (Mirza coquereli). Like all other lemurs, they are native to Madagascar, where they are found in the western dry deciduous forests and further to the north in the Sambirano Valley and Sahamalaza Peninsula. First described in 1867 as a single species, they were grouped with mouse lemurs and dwarf lemurs. In 1870, British zoologist John Edward Gray assigned them to their own genus, Mirza. The classification was not widely accepted until the 1990s, which followed the revival of the genus by American paleoanthropologist Ian Tattersall in 1982. In 2005, the northern population was declared a new species, and in 2010, the World Wide Fund for Nature announced that a southwestern population might also be a new species.
Giant mouse lemurs are about three times larger than mouse lemurs, weighing approximately , and have a long, bushy tail. They are most closely related to mouse lemurs within Cheirogaleidae, a family of small, nocturnal lemurs. Giant mouse lemurs sleep in nests during the day and forage alone at night for fruit, tree gum, insects, and small vertebrates. Unlike many other cheirogaleids, they do not enter a state of torpor during the dry season. The northern species is generally more social than the southern species, particularly when nesting, though males and females may form pair bonds. The northern species also has the largest testicle size relative to its body size among all primates and is atypical among lemurs for breeding year-round instead of seasonally. Home ranges often overlap, with related females living closely together while males disperse. Giant mouse lemurs are vocal, although they also scent mark using saliva, urine, and secretions from the anogenital scent gland.
Predators of giant mouse lemurs include the Madagascar buzzard, Madagascar owl, fossa, and the narrow-striped mongoose. Giant mouse lemurs reproduce once a year, with two offspring born after a 90-day gestation. Babies are initially left in the nest while the mother forages, but are later carried by mouth and parked in vegetation while she forages nearby. In captivity, giant mouse lemurs will breed year-round. Their lifespan in the wild is thought to be five to six years. Both species are listed as endangered due to habitat destruction and hunting. Like all lemurs, they are protected under CITES Appendix I, which prohibits commercial trade. Despite breeding easily, they are rarely kept in captivity. The Duke Lemur Center coordinated the captive breeding of an imported collection of the northern species, which rose from six individuals in 1982 to 62 individuals by 1989, but the population fell to six by 2009 and was no longer considered a breeding population.
Taxonomy
The first species of giant mouse lemur was described by the French naturalist Alfred Grandidier in 1867 based on seven individuals he had collected near Morondava in southwestern Madagascar. Of these seven specimens, the lectotype was selected in 1939 as MNHN 1867–603, an adult skull and skin. Naming the species after the French entomologist Charles Coquerel, Grandidier placed Coquerel's giant mouse lemur (M. coquereli) with the dwarf lemurs in the genus Cheirogaleus (which he spelled Cheirogalus) as C. coquereli. He selected this generic assignment based on similarities with fork-marked lemurs (Phaner), which he considered to also be members of Cheirogaleus. The following year, the German naturalist Hermann Schlegel and Dutch naturalist François Pollen independently described the same species and coincidentally gave it the same specific name, coquereli, basing theirs on an individual from around the Bay of Ampasindava in northern Madagascar. Unlike Grandidier, they placed their specimen in the genus Microcebus (mouse lemurs); however, these authors also listed all Cheirogaleus under Microcebus and based the classification of their species on similarities with the greater dwarf lemur (M. typicus, now C. major).
In 1870, the British zoologist John Edward Gray placed Coquerel's giant mouse lemur into its own genus, Mirza. This classification was widely ignored and later rejected in the early 1930s by zoologists Ernst Schwarz, Guillaume Grandidier, and others, who felt that its longer fur and bushy tail did not merit a separate genus and instead placed it in Microcebus. British anatomist William Charles Osman Hill also favored this view in 1953, noting that despite its larger size (comparable to Cheirogaleus), its first upper premolar was proportionally small as in Microcebus. In 1977, French zoologist Jean-Jacques Petter also favored the Microcebus classification, despite the threefold size difference between Coquerel's giant mouse lemur and the other members of the genus.
The genus Mirza was resurrected in 1982 by American paleoanthropologist Ian Tattersall to represent an intermediate branch between Microcebus and Cheirogaleus, citing the Coquerel's giant mouse lemur's significantly larger size than the largest Microcebus and locomotor behavior more closely aligned with Cheirogaleus. Adoption of Mirza was slow, though in 1994 it was used in the first edition of Lemurs of Madagascar by Conservation International. In 1993, primatologist Colin Groves initially favored the Microcebus classification in the second edition of Mammal Species of the World, but began supporting the resurrection of Mirza in 2001. In 1991, prior to adopting Mirza, Groves was the first to use the common name "giant mouse lemur". Prior to that, they were popularly referred to as "Coquerel's mouse lemur".
In 2005, Peter M. Kappeler and Christian Roos described a new species of giant mouse lemur, the northern giant mouse lemur (M. zaza). Their studies compared the morphology, behavioral ecology, and mitochondrial cytochrome b sequences of specimens from both Kirindy Forest in central-western Madagascar and around Ambato in northwestern Madagascar, part of the Sambirano valley. Their study demonstrated distinct differences in size, sociality, and breeding, as well as sufficient genetic distance to merit specific distinction between the northern and central-western populations. Because Grandidier's description was based on a southern specimen, they named the northern population as a new species.
The World Wide Fund for Nature (WWF) announced in 2010 that a biodiversity study from 2009 in the gallery forest of Ranobe near Toliara in southwestern Madagascar revealed a population of giant mouse lemurs previously unknown to science, and possibly a new species. They noted a significant difference in coloration between the two known species and the specimen they observed. However, further testing was required to confirm the discovery.
Etymology
The etymology of Mirza puzzled researchers for many years. Gray often created mysterious and unexplained taxonomic names—a trend continued with his description of not only Mirza in 1870, but also the genera Phaner (fork-marked lemurs) and Azema (for M. rufus, now a synonym for Microcebus), both of which were described in the same publication. In 1904, American zoologist Theodore Sherman Palmer attempted to document the etymologies of all mammalian taxa, but could not definitively explain these three genera. For Mirza, Palmer only noted that it derived from the Persian title mîrzâ ("prince"), a view tentatively supported by Alex Dunkel, Jelle Zijlstra, and Groves in 2012. However, because the reference to Persian princes might have come from Arabian Nights, a popular piece of literature at the time, Dunkel et al. also searched the general literature published around 1870. The origin of all three names was found in a 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 all three names: King Phanor (sic), Mirza, and Azema. The authors concluded that Gray had seen the comedy and then based the names of three lemur genera on its characters.
Evolution Based on studies using morphology, immunology, repetitive DNA, SINE analysis, multilocus phylogenetic tests, and mitochondrial genes (mtDNA), giant mouse lemurs are most closely related to mouse lemurs within the family Cheirogaleidae, and together they form a clade with the hairy-eared dwarf lemur (Allocebus). Both dwarf lemurs and fork-marked lemurs are more distantly related, with fork-marked lemurs being either a sister group of all cheirogaleids, or more closely related to sportive lemurs (Lepilemur).
Although Mirza, Microcebus, and Allocebus form a clade within Cheirogaleidae, the three lineages are thought to have diverged during a narrow window of time, so the relationships within this clade are difficult to determine and may change with further research. All three are thought to have diverged at least 20 mya (million years ago), although another estimate using mtDNA places the divergence between Mirza and Microcebus at 24.2 mya. Divergence between the two recognized species of giant mouse lemur is estimated at 2.1 mya.
Description Though giant mouse lemurs are relatively small cheirogaleids, they are more than three times larger than the smallest members of the family, the mouse lemurs. Their body weight averages . At around , their bushy and long tail is longer than their head-body length, which averages . Their forelimbs are shorter than the hind limbs (with an intermembral index of 70), a trait shared with mouse lemurs. The skull is similar to that of dwarf and mouse lemurs, and the auditory bullae are small.
Like other cheirogaleids, the dental formula for giant mouse lemurs is ; 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. Their upper teeth converge towards the front of the mouth, but are straighter than those in mouse lemurs. The first upper premolar (P2) is relatively small, but nearly as tall as the next premolar (P3). Unlike mouse lemurs and more like dwarf lemurs, giant mouse lemurs have a prominent anterior lower premolar (P2). Also more aligned with dwarf lemurs, the first two upper molars (M1–2) have a more anterior hypocone that sits opposite the metacone, compared to the mouse lemurs' more posterior hypocone, which is presumably a symplesiomorphic (ancestral) trait. Also on M1 and M2, the cingulum (a crest or ridge on the tongue side) comprises two small cuspules. In all other dental characteristics, giant mouse lemurs are noticeably similar to both dwarf and mouse lemurs.
Giant mouse lemurs have two pairs of mammae, one on the chest (pectoral) and one on the abdomen (abdominal). Their fur is typically grayish-brown on the dorsal (back) side and more gray in color on the ventral (front) side. The tail is typically black-tipped. The new population found by WWF in 2010 has an overall lighter color, along with reddish or rusty patches near the hands and feet on the dorsal side of the arms and legs. This population also has a red tail, which darkens at the end. Vibrissae are found above the eyes (superciliary), above the mouth (buccal), under the lower jaw (genal), near the top of the jaw (interramal), and on the wrist (carpal). Like mouse lemurs, the ears are large and membranous.