EXTANT STREPSIRRHINES

The Malagasy lemurs comprise a total of about 32 species further classified into 14 genera and 5 families, all unique to Madagascar. These primates display an extraordinary array of morphologies, behaviors and lifestyles, thus making them a fascinating group for study in a variety of scientific fields. In the 1970's, several papers were published that questioned the phylogenetic unity of the Malagasy primate lineage. These papers were primarily concerned with the phylogenetic position of the mouse and dwarf lemur group (family Cheirogaleidae) relative to the Afro-Asian galagos and lorises (infraorder Lorisiformes), concluding that the two groups form a clade that excludes the remaining Malagasy primates. The phylogenetic position of the aye-aye (Daubentonia madagascariensis) has also been considered problematic. Its bizarre morphology and unusual ecological specializations have made phylogenetic placement within the Strepsirrhini difficult. The phylogenetic confusion has therefore made it difficult to arrive at a realistic biogeographic model to explain the presence of primates on Madagascar. In an effort to resolve these phylogenetic and biogeographic issues, I have spent the past several years analyzing both the morphology and select regions of the genome for a large sample of strepsirrhine taxa (Yoder 1994; Yoder 1996; Yoder et al. 1996a&b; Yoder 1997). These studies have yielded a robust phylogenetic hypothesis that, in addition to its agreement with other molecular phylogenetic studies, provides an elegant model of lemur origins. Analyses have demonstrated that the diverse primate fauna of Madagascar is monophyletic and thus the product of a single colonization of an ancestral primate that arrived from Africa, probably during the early Eocene. It is certain, however, that there was no land bridge or other fully-terrestrial means for such a migration at this time or within the previous tens of millions of years. The question therefore persists: How did lemurs manage to cross the formidable water barrier that we now know as the Mozambique channel?

Photograph: Avahi laniger (near Mananara)