Fork-marked lemurs or fork-crowned lemurs are strepsirrhine primates; the four species comprise the genus Phaner. Like all lemurs, they are native to Madagascar, where they are found only in the west, north, and east sides of the island. They are named for the two black stripes which run up from the eyes, converge on the top of the head, and run down the back as a single black stripe. They were originally placed in the genus Lemur in 1839, later moved between the genera Cheirogaleus and Microcebus, and given their own genus in 1870 by John Edward Gray. Only one species (Phaner furcifer) was recognized, until three subspecies described in 1991 were promoted to species status in 2001. New species may yet be identified, particularly in northeast Madagascar.
Fork-marked lemurs are among the least studied of all lemurs and are some of the largest members of the family Cheirogaleidae, weighing around or more. They are the most phylogenetically distinct of the cheirogaleids, and considered a sister group to the rest of the family. Aside from their dorsal forked stripe, they have dark rings around their eyes, and large membranous ears. Males have a scent gland on their throat, but only use it during social grooming, not for marking territory. Instead, they are very vocal, making repeated calls at the beginning and end of the night. Like the other members of their family, they are nocturnal, and sleep in tree holes and nests during the day. Monogamous pairing is typical for fork-marked lemurs, and females are dominant. Females are thought to have only one offspring every two years or more.
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. All four species are endangered. Their populations are in decline due to habitat destruction. Like all lemurs, they are protected against commercial trade under CITES Appendix I.
Taxonomy
Fork-marked lemurs were first documented in 1839 by Henri Marie Ducrotay de Blainville when he described the Masoala fork-marked lemur (P. furcifer) as Lemur furcifer. The holotype is thought to be MNHN 1834-136, a female specimen taken from Madagascar by French naturalist Jules Goudot. The source of this specimen is unknown, but thought to be Antongil Bay. In 1850, Isidore Geoffroy Saint-Hilaire moved the fork-marked lemurs to the genus Cheirogaleus (dwarf lemurs), but they were also commonly listed in the genus Microcebus (mouse lemurs). In 1870, John Edward Gray assigned fork-marked lemurs to their own genus, Phaner, after initially including them and the mouse lemurs in the genus Lepilemur (sportive lemurs). Although French naturalist Alfred Grandidier accepted Gray's new genus (while also lumping the other cheirogaleids in Cheirogaleus and illustrating the cranial similarities between cheirogaleids and Lepilemur) in 1897, the genus Phaner was not widely accepted. In the early 1930s, Ernst Schwarz, Guillaume Grandidier, and others resurrected the name, citing characteristics that were intermediate between Cheirogaleus and Microcebus.
Until the late 20th century, there was only one recognized species of fork-marked lemur, although size and coloration differences had been noted previously. After comparing museum specimens, paleoanthropologist Ian Tattersall and physical anthropologist Colin Groves recognized three new subspecies in 1991: the Pale fork-marked lemur (P. f. pallescens), Pariente's fork-marked lemur (P. f. parienti), and the Amber Mountain fork-marked lemur (P. f. electromontis). In 2001, Groves elevated all four subspecies to species status 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, the arrangement is generally accepted.
In December 2010, Russell Mittermeier of Conservation International and conservation geneticist Edward E. Louis Jr. announced the possibility of a new species of fork-marked lemur in the protected area of Daraina in northeast Madagascar. In October, a specimen was observed, captured, and released, although genetic tests have yet to determine if it is a new species. The specimen demonstrated a slightly different color pattern from other fork-marked lemur species. If shown to be a new species, they plan to name it after Fanamby, a key conservation organization working in that protected forest.
Etymology The etymology of the genus Phaner puzzled researchers for many years. Gray often created mysterious and unexplained taxonomic names. 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". In 2012, Alex Dunkel, Jelle Zijlstra, and Groves attempted to solve the mystery. 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. Since the genera Mirza (giant mouse lemurs) and Azema (for M. rufus, now a synonym for Microcebus) were both described in the same publication and equally enigmatic, the authors concluded that Gray had seen the comedy and then based the names of three lemur genera on its characters.
Fork-marked lemurs were called "fork-marked dwarf lemurs" by Henry Ogg Forbes in 1894 and "fork-crowned mouse lemur" by English missionary and naturalist James Sibree in 1895. Literature searches by Dunkel et al. also uncovered other names, such as "fork-lined lemur" and "squirrel lemur", during the early 1900s. By the 1970s, reference to dwarf and mouse lemurs had ended, and the "fork-crowned" prefix became popular between 1960 and 2001. Since then, the "fork-marked" prefix has become more widely used. These lemurs get their common name from the distinctive forked stripe on their head.
Evolution
Within the family Cheirogaleidae, fork-marked lemurs are the most phylogenetically distinct, although their placement remained uncertain until recently. One uniting characteristic (synapomorphy) among all cheirogaleids, to the exclusion of other lemurs, is the branching of the carotid artery along with how it enters the skull—a trait which is shared by fork-marked lemurs. Analyses based on morphology, immunology, and repetitive DNA have given contradictory placements of Phaner, while studies in 2001 and 2008 either lacked data or yielded poor resolution of their placement.
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. A study published in 2013 also grouped fork-marked lemurs with sportive lemurs when it used 43 morphological traits and mtDNA. If correct, this would make the family Cheirogaleidae paraphyletic. Broad agreement between two lemur phylogeny studies—one in 2004 using SINE analysis and another in 2012 using multilocus phylogenetic tests—gave strong support for a sister group relationship between fork-marked lemurs and the rest of the cheirogaleids and a more distant relationship with sportive lemurs. The split between Phaner and the rest of the cheirogaleids is thought to have occurred approximately 38 mya (million years ago), not long after the radiation of most of the major lemur groups on Madagascar, roughly 43 mya.
Description
Of the mostly small, nocturnal lemurs in family Cheirogaleidae, the genus Phaner contains some of the largest species, along with Cheirogaleus. Their body weight ranges between , and their head-body length averages between , with a tail length between .
Fork-marked lemurs' dorsal (back) fur is either light brown or light grayish-brown, while their ventral (underside) fur can be yellow, cream, white, or pale brown. A black stripe extends from the tail, along the dorsal midline to the head, where it forks at the top of the head in a distinguishing Y-shape leading to the dark rings around both eyes, and sometimes extends down the snout. The dorsal stripe varies in width and darkness. The base of the tail is the same color as the dorsal fur and is usually tipped in black; the tail is bushy. The lemurs' ears are relatively large and membranous. Males have a scent gland on the middle of their throat, which is approximately wide and pink in color. Females have a narrow, bare patch of white skin in the same location, but theirs does not appear to produce secretions.
These lemurs have relatively long hindlegs. For gripping tree trunks and large branches, they have large hands and feet with extended pads on the digits, as well as claw-like nails. They have a long tongue which assists obtaining the gum and nectar, as well as a long caecum, which helps digest gums. Their procumbent (forward-facing) lemuriform toothcomb (formed by the lower incisors and canines) is long and more compressed, with significantly reduced interdental spaces to minimize the accumulation of gum between the teeth.
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. The fork-marked lemur dental formula 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 first incisor (I1) is long and curved towards the middle of the mouth (unique among lemurs), while the second upper incisor (I2) is small with a gap (diastema) between the two. The upper canines are large, with their tips curved. Their upper anterior premolars (P2) are caniniform (canine-shaped) and more pronounced than in any other living lemur. The next upper premolar (P3) is very small, 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. The two cusps on the last upper premolar (P4) are a large paracone and a smaller protocone. Like other cheirogaleids, their first lower premolar (P2) is caniniform and large, while the cingulids (ridges) on the three lower premolars are more developed compared to most other cheirogaleids. The first two upper molars (M1–2) have a developed hypocone, and the buccal cingulum (a crest or ridge on the cheek side) is well developed on all three upper molars. The molars are relatively small compared to other cheirogaleids, with the second upper and lower molars (M2 and M2) having reduced functionality compared to those of mouse lemurs.
Males have relatively small testes compared to other lemurs, and their canine teeth are the same size as those seen in females. During the dry season, females can weigh more than males. Both patterns of sexual dimorphism are consistent with the theory of sexual selection for monogamous species and female dominance respectively. Females have two pairs of nipples.
Distribution and habitat