Evolution and systematics

There is one extinct genus Megaladapis, or koala lemur, within the family Lepilemuridae, and within that extinct genus there are three extinct species Megaladapis madagascariensis, M. edwardsi, and M. grandidieri. Megaladapis grandidieri was known to exist (from subfossil material) from Ampasambaz-imba in central Madagascar, while M. madagascariensis and M. edwardsi were known to exist from southwestern and southern Madagascar.

Koala lemurs were very impressive during their time because, according to fossil skulls that have been found, their skulls were as large as that of the skull of an ass; and with a deduced head and body weight of 88-176 lb (40-80 kg). Such subfossil remains have been found during the last quarter of the twentieth century at sites in Madagascar, and date back (with radiocarbon dating procedures) about 600-3,000 years ago. Humans began to populate Madagascar during this period, moving in with domestic livestock. This put environmental pressure on the koala lemurs with respect to reduced natural forest habitat and a very aggressive human predator

(they were earlier evolving without predators). In addition, drought was believed to have increased pressures during this time with respect to them. Koala lemurs probably became extinct sometime prior to the arrival of Europeans during the 1500s. In 1982 Tattersall indicated a similarity between the koala lemur and the prosimian ("primitive ape") family Adapidae of the Eocene Epoch (55-38 million years ago) of Europe.

From cranial and postcranial morphology, the locomotion and lifestyle of koala lemurs were similar to that of Phascolarc-tos, the living koalas of Australia. The skull was very large in relation to the short, bulky postcranial skeleton; and relatively narrow, greatly elongated, and resembling the skull of a pig. Cranial length of Megaladapis grandidieri was 10.8-11.8 in (27.3-30.0 cm), while the length of M. madagascariensis was 9.3-9.6 in (23.5-24.4 cm). Both species' postcranial specializations suggested that they had a greater flexibility of their limbs and most likely a more distinct arboreal (tree climbing) adaptation than M. edwardsi. Hind limb suspension was in all likelihood an important behavior of both animals. Cranial length

A white-footed sportive lemur (Lepilemur leucopus) in a tree in Berenty, Madagascar. (Photo by Nigel J. Dennis/Photo Researchers, Inc. Reproduced by permission.)

of M. edwardsi was 10.9-12.5 in (27.7-31.7 cm); it possessed one of the largest sized cranial lengths of known prosimians.

The facial area of koala lemurs was long, the orbits divergent, the auditory bullae flat, and the braincase very small. The long nasal bones projected well past the anterior end of the palate; this feature tends to indicate to researchers that they had a moveable snout when alive. The zygomatic arches (the bone bar that connects the cheekbone with the temporal bone on the side of the skull) were massive, and there were strong nuchal (with respect to the nape of the neck) and sagittal (with respect to the suture at the top of the skull) crests. The foramen magnum (the opening at the base of the skull) was rotated back onto the posterior surface of the skull so that it faced forward when the species stood on all four feet. The occipital condyles (the knobs on each side of the foramen magnum) were oriented perpendicularly to the cranial base. Adults had no upper incisor teeth, instead had bony ridges that suggested a horny pad (similar to some ungulate herbivores). The large molars were complex cusps and increased in size from the front to the rear.

Hands and feet were extraordinarily long, but the legs were relatively short. The forelimbs were longer than the hind limbs, and all four powerful legs were somewhat curved, shaped for grasping. They clung to tree trunks and branches with all forelimbs, and moved upward with a series of short hops. Koala lemurs crossed to neighboring trees with short leaps. They fed by cropping leaves pulled by its forelimbs that were within easy reach of the mouth.

The white-footed sportive lemur (Lepilemur leucopus) is able to leap a distance of 16 ft (5 m). (Photo by © Gallo Images/Corbis. Reproduced by permission.)

The living genus Lepilemur had for a long time been placed in the family Lemuridae. However, according to Rumpler (1975), Rumpler and Albignac (1975), and Petter and Petter-Rousseaux (1979), systematic investigations, which included cytogenetics (the scientific study of chromosomes), showed

A red-tailed sportive lemur (Lepilemur ruficaudatus) in front of its tree nest. (Photo by Harald Schutz. Reproduced by permission.)

that it represented a separate family and, therefore, took the family name Lepilemuridae. Later research by Buettner-Janusch and Tattersall (1985) and Tattersall (1982 and 1986) indicated that Lepilemur belonged in the same family as the extinct Megaladapis and, therefore, the family name was indicated to be Megaladapidae. Several studies in the late 1980s and early 1990s conflicted as to which family (Lemuridae, Lepilemuridae, or Megaladapidae) Lepilemur should be placed. (It is the contention of the experts collaborating on this publication that the extinct genus Megaladapis and the extant genus Lepilemur will be placed in the family Lepilemuridae.)

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