Adaptive diversity in subfossil Malagasy prosimians

Abstract

The island of Madagascar exhibits an exceptional degree of topographical, climatic, and ecological diversity. This great internal complexity has been characterized by Martin (1972) as similar to closed group of (somewhat elastic) islands. The evolutionary implications of such a situation are readily apparent; the colonizing prosimian fauna no doubt encountered numerous op portunities for geographical separation of different populations, allopatric speciation, and subsequent competition leading to niche specializations. The considerable diversity in behavioral and morphological adaptations among living Malagasy prosimians strongly supports such an adaptive radiation scenario (Petter et al., 1977). Moreover, if recently extinct (subfossil) forms are taken into account, the entire remainder of the primate order strains to find suitable morphological and eco-ethological analogies to the Malagasy prosimians (Tatter sall, 1973 a; Walker, 1974). It is possible to demonstrate quite close taxonomic relationships among various subf ossil and extant Malagasy lemurs (Table 1). All recognized families except the Cheirogaleidae possess both living and extinct representatives. Pachylemur is the lone subf ossil member of the Lemuridae; similary, Megaladapis (three species) is the only extinct representative of the Lepilemuridae. Daubentonia robustus is little more than a larger, more robust form of the living aye-aye. Only within the Indriidae are there more known subfossil than living genera. Several of the subfossil deposits have yielded extinct specimens in association with living species (e. g., Lemur catta and Propithecus verreauxi at Andrahomana in association with Archaeolemur and Megaladapis), and radiocarbon dating of the various localities spans a narrow period of approximately 1,000?3,000 years B. P. (Tattersall, 1973 b). One of the most consistent differences between the living and the subfossil members of each family is that of size; the extinct forms tend to be larger than