Evolution and systematics

The evolutionary history of the Malagasy prosimians has been, until recently, one of the knottiest in the life sciences. As of 2000, cladistic analyses, genetic and mitochondrial DNA studies, and morphological comparisons support a mono-phyletic (single species) origin of all Malgasy prosimians from a founder species that rafted on vegetation from Africa to Madagascar in the early Eocene epoch (55 to 34 million years ago).

There are at least 60 known species of Malagasy prosimians, living and recently extinct, all generally lumped under the umbrella name "lemurs." The total includes 15 large-bodied species, most with unique adaptations, that became extinct within the last 200-300 years. "Lemuridae" is used here as referring to the so-called true lemurs, house cat-sized with fairly long, fox-like muzzles.

Lemurs are prosimians (suborder Prosimii), the term "prosimian" is loosely translated as "pre-monkey" and covers several lines of primate evolution diverging from those of the anthropoids (suborder Anthropoidea: monkeys, apes, and ho-minids). Living prosimian species include the prosimians of

Madagascar (superfamily Lemuroidea), the lorisoids, and the tarsiers. The lorisoids (superfamily Lorisoidea) include the galagos (bushbabies) and pottos of the African mainland and the lorises of Southeast Asia. There are only three living species of tarsiers (infraorder Tarsiiformes, superfamily Tar-siodea), small, headlight-eyed, goblinesque arboreal primates found on some of the Southeast Asian islands.

The eye socket of the skull is open in prosimians but closed in anthropoids. Prosimians have mostly nails on their digits, except for the second digit of the hind foot, which carries a claw or clawlike nail used for self-grooming; anthropoids have only nails on all digits (with the distant exception of the neotropical marmosets and tamarins). Prosimians' lower canines and incisors are modified into a comblike structure used as a grooming tool; anthropoids have no such structure.

Suborder Strepsirrhini ("wet nose") covers lemurs and lorisoids, since those species keep the generalized mammalian condition of noses wet by self-licking to facilitate the olfactory sense, obvious in animals like dogs and cats. In strepsir-rhines, the upper lip is divided, again as in dogs and cats, to

Greater bamboo lemur (Hapalemur simus) mother and baby live in the trees of Madagascar. (Photo by Harald Schutz. Reproduced by permission.)

make way for the frequent nose-lapping tongue. Tarsiers, monkeys, apes, and hominids are placed in suborder Haplor-rhini ("dry nose"), since they have discarded the split lip and the wet nose, coming to rely more on vision and less on olfaction.

Ringtailed lemur (Lemur catta) baby clings to its mother's back. (Photo by John Giustina. Bruce Coleman, Inc. Reproduced by permission.)
A mongoose lemur (Lemur mongoz) drinks out of a tree trunk. (Photo by Harald Schütz. Reproduced by permission.)

There are several differing classifications of lemur species, all in fluctuation as the latest studies in morphology and DNA comparison studies of lemurs reveal new interrelationships among species. The other families of living Malagasy prosimi-ans, not covered in this entry, are Cheirogaleidae, the dwarf and mouse lemurs; Lepilemuridae, the weasel or sportive lemurs; Indriidae, covering the indris, sifakas, and avahis; and Daubentoniidae, the specialized, enigmatic aye-aye.

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