I. Geoffroy, 1851
General characteristics
The genus Lepilemur was placed in a separate family by Petter et al., 1977 since it is clearly distinct from the four genera of the Lemuridae family, with which it was first classified. The Lepilemur family possesses unique characteristics that separate it from the Lemuridae. The size of Lepilemur (head and body) does not exceed 25 to 35 cm, and the tail is almost as long as the body. The upper incisors are missing. The animals essentially move by jumping from trunk to trunk, but they keep their bodies in an upright position, which clearly distinguishes them from Eulemur and Lemur.
During the day, they take refuge in a shelter to be hidden from sunlight and having a minimal amount of protection. In this way, the animals may settle in a hollow trunk or tree hole. However, in the South or Northeast, they are regularly found closely packed together against a trunk, sheltered by foliage. They especially feed on leaves and have a very specialized digestive system, which differentiates them from all other lemurs. Lepilemur is found in natural forest all over Madagascar. They live solitarily but many animals also form small core populations. These nocturnal animals are widely distributed in Madagascar, and generally their presence is easily noticed because of very variable calls that almost every species produces at dusk.
The genus Lepilemur is well defined by its anatomical characters, and the genera Galeocebus (Wagner, 1855), Mixocebus (Peters, 1875), and Lepidolemur (Peters, 1875) are considered synonymous (Simpson, 1945; Hill, 1953). The name Lepilemur is now commonly used despite the fact that according to Petit, 1933 the name Lepilemur was a typographical error as the word does not mean anything. The name Lepidolemur should be used instead. The name Lepilemur is indeed mentioned in the text of I. Geoffroy in 1851, but has been corrected in the first part of its Methodological Catalogue of the Collection of Mammals and should be used according to article 32 (ii) of the International Code of Zoological Nomenclature (1961: 43).
Systematics
The genus Lepilemur is one of the Malagasy genera of which the systematics presents many difficulties due to its widespread distribution (it is found in almost all forests of the island) and its variability. Numerous authors (Geoffroy, 1851; Grandidier, 1867; Gray, 1870; Peters, 1875; Forsyth Major, 1894; Lorenz, 1898; Milne-Edwards and Grandidier, 1897) have successively described the various collected specimen types. However from the first publications and onwards, the large resemblance between some of these forms led to confusion and to a number of revisions.
The imprecision of the places of origin of the obtained specimens did not contribute to resolving this matter. Three 'new' essays on the classification did not take into account the entire complexity of the problem (Schwarz, 1931; Petit, 1933; Hill, 1953).
In his work, Hill adopted the classification proposed by Schwarz. The genus only consisted of two species of which the second comprised two subspecies, whereas the other forms were considered synonymous. In a more recent revision of this genus (Petter and Petter-Rousseaux, 1960) a new attempt was made to base a classification on the analysis of pelage and skulls of a certain number of collections and on particular field observations. In the absence of any difference in cranial sections, this new study led to the conclusion that this genus only contained one species whose variations, although much less apparent, were parallel with those of for example Eulemur. As all specimens are brown colored, only differences in shade and size could be used for distinction between the animals. Five forms that were considered as geographical subspecies were characterized and grouped within Lepilemur mustelinus.
In 1956, during their first visit to Madagascar, J.-J. Petter and A. Petter-Rousseaux visited various regions of the island in an attempt to study the behavioral ecology of several forms of Lepilemur in their natural environment, with aid of electric lamps and infrared telescope. After that field study, it was decided to make a complete revision of the genus by studying specimens in the most important collections of the principal museums (Petter and Petter-Rousseaux, 1960). 153 specimens were studied at the National Museum of Natural History in Paris, the British Museum of National History, the Tring Museum, and the collections at Tananarive. These museum collections and field observations led to the conclusion that the majority of specimens are easily classified into distinct populations of different geographical distribution. In addition, these populations equally differed in size, pelage details, and in their behavior.
A certain number of names, given to these specimens accompanied with labels of origin, have been retrieved through bibliographical searches. To summarize:
- L. mustelinus (Geoffroy, 1851). The type specimen was probably acquired by J. Goudot at the eastern coast, north of Tamatave and preserved at the National Museum of Natural History in Paris. The specimen resembled the animals of the area of Alaotra Lake and those living in the northern parts of the forest in the East (Rode, 1939).
- L. ruficaudatus (Grandidier, 1867). The type specimen was obtained by Grandidier in the Morondava area and was preserved at the National Museum of Natural History in Paris (Rode, 1939).
- L. dorsalis (Gray, 1870). The type specimen was obtained by D. van Dam in the Northeast of Madagascar and preserved in a bad state with missing skull at the British Museum of Natural History. Later this name was used by Petit, 1933 to describe a specimen found in the West, between the eastern bank of the river Betsiboka and the Sambirano heights, as well as at Nosy Be.
- L. pallidicauda (Gray, 1873). The type specimen collected by A. Crossley in the Morondava region and preserved at the British Museum of Natural History.
- L. caniceps (Peters, 1875). The type specimen is preserved in Berlin and described under the name of Mixocebus caniceps. A. Crossley collected the specimen, a young female, in the East in 1872. It had a pair of incisors in the upper jaw, which is unusual for an adult. Therefore, this animal is most probably a young L. mustelinus.
- L. edwardsi (Forsyth Major, 1894). The type specimen is collected by J. T. Last at the northern shore of the Bombetoka Bay, which is an estuary of the Betsiboka River, and it is stored at the British Museum of Natural History.
- L. globiceps (Forsyth Major, 1894). The type specimen collected 25 km north of Tulear by J. T. Last, and preserved in alcohol at the British Museum of Natural History (Schwarz, 1931). However, Petter and Petter-Rousseaux were unable to find the specimen there. By studying the description of Elliot, 1900, one may conclude that the animal most probably was a L. leucopus.
- L. grandidier (Forsyth Major, 1894). The type specimen is collected by D. van Dam in the Northeast of Madagascar and preserved at the British Museum of Natural History.
- L. microdon (Forsyth Major, 1894). The type specimen is collected by W.D. Cowan in the East of the Betsileo land (heights of Masiatra) and preserved at the British Museum of Natural History. The specimen corresponded to the animals from the southern parts of the forest in the East.
- L. leucopus (Forsyth Major, 1894). The type specimen is collected in the Fort Dauphin region and preserved at the British Museum of Natural History.
- L. mustelinus rufescens (Lorenz, 1898). The type specimen collected by A. Voeltzkow on the riverbank north of the Bombetoka Bay and it is preserved at the Senckenberg Museum, at Frankfurt am Main.
In spite of the research done by Petter and Petter-Rousseaux, the systematics of this group still remains rather confusing. It would have been very difficult to get a clear picture without the cytogenetic studies started by Yves Rumpler in 1986.
Certain 'forms' correspond with types, which are defined by results obtained from cytogenetic research.
-(2N = 20): ruficaudatus A. Grandidier, 1867 (= pallicauda Gray, 1873)(Karyo L. ruficaudatus)
-(2N = 22): edwardsi Forsyth Major, 1894 (= rufescens Lorenz, 1898)(Karyo L. edwardsi)
-(2N = 26): dorsalis Gray, 1870 (= grandidieri Forsyth Major, 1894)(Karyo L. dorsalis)
-(2N = 34, 36 and 38): septentrionalis Rumpler and Albignac, 1975
(2N = 38): septentrionalis andrafiamenensis Rumpler and Albignac, 1975 (1)
(2N = 36): septentrionalis ankaranensis Rumpler and Albignac, 1975 (2)(Karyo L. s. ankaranensis)
(2N = 36): septentrionalis sahafarensis Rumpler and Albignac, 1975 (3)
(2N = 34): septentrionalis septentrionalis Rumpler and Albignac, 1975 (4)
-(2N = 34): mustelinus I. Geoffroy, 1851(Karyo L. mustelinus)
-(2N = ?): microdon Forsyth Major, 1894
-(2N = 26): leucopus Forsyth Major, 1894 (= globiceps Forsyth Major, 1894)(Karyo L. leucopus)
(1) Holotype: 1 male, Madagascar North, Massif of Andrafiamena (Muséum national d'Histoire naturelle, Paris, Cat. Mamm. Ois., 1974 no 79)
(2) Holotype: 1 female, Madagascar North, forest of Analamerana (Muséum national d'Histoire naturelle, Paris, Cat. Mamm. Ois., 1974 no 77)
(3) Holotype: 1 male, Madagascar North, forest of Sahafary (Muséum national d'Histoire naturelle, Paris, Cat. Mamm. Ois., 1974 no 78)
(4) Holotype: 1 female, Madagascar North, forest of Sahafary (Muséum national d'Histoire naturelle, Paris, Cat. Mamm. Ois., 1974 no 80)
After the analysis of the above mentioned research and the works of Y. Rumpler, it is now possible to identify seven different species to which yet another species should be added that was mixed up with Lepilemur ruficaudatus. However, the existence of this species needs to be verified. Provisionally, the species may correspond with Lepilemur pallicauda Gray, 1873 and with a relatively large sized form that was observed by R. Albignac near the summit of Tsaratanana.
The different species are listed in order corresponding to their distribution from North to South, and a) corresponds with West and b) with East:
a) Lepilemur septentrionalis Rumpler and Albignac, 1975 (with 4 subspecies)
a) Lepilemur dorsalis Gray, 1870
a) Lepilemur edwardsi (Forbes, 1894)
a) Lepilemur pallidicauda (Gray, 1873)
a) Lepilemur ruficaudatus A. Grandidier, 1867
a) Lepilemur leucopus (Major, 1894)
b) Lepilemur microdon (Forbes, 1894)
b) Lepilemur mustelinus I. Geoffroy, 1851
The existence of very similar forms that are only differentiable by cytogenetic comparison, as well as the existence of natural hybrids between neighboring forms, indicates that speciation within the genus Lepilemur is still in process. Any pronounced chromatic differentiation between the different forms is not very clear because evolutionary selection on small species sensitive to predation probably made this impossible. Only rather dark brown-colored forms, which can merge with their background, survive. According to Y. Rumpler, 1974, a possible pattern of chromosomal evolution in Lepilemur could be the development from a primitive chromosomal formula to a chromosomal formula with a large proportion of acrocentric chromosomes. Centric fusion, pericentric inversion, and translocations play a major role within Lepilemur, contrary to Eulemur within which a centric fusion is a chromosomal modification that occurs rather rarely.