the other megafauna that once existed on the large island. Additional factors are thought to have contributed to their ultimate disappearance. Oral traditions and recent reports of sightings by Malagasy villagers have been interpreted by some as suggesting either lingering populations or very recent extinctions. Diversity Extinct giant lemurs Until recently, giant lemurs existed in Madagascar. Although they are only represented by subfossil remains, they were modern forms, having adaptations unlike those seen in lemurs today, and are counted as part of the rich lemur diversity that has evolved in isolation for up to 60 million years. All 17 extinct lemurs were larger than the extant forms, including the largest living lemurs, the indri (Indri indri) and diademed sifaka (Propithecus diadema), which weigh up to . The estimated weights for the subfossil lemurs have varied. Techniques used for these weight estimations include the comparison of skull lengths, tooth size, the head diameter of the femur, and more recently, the area of cortical bone (hard bone) in long bones (such as the humerus). Despite the variations in the size estimates for some species, all subfossil lemurs were larger than living species, weighing or more, and one species may have weighed as much as . All but one species, the giant aye-aye, are thought to have been active during the day. Not only were they unlike the living lemurs in both size and appearance, they also filled ecological niches that no longer exist or are now left unoccupied. Their remains have been found in most parts of the island, except for the eastern rainforests and the Sambirano domain (seasonal moist forests in the northwest of the island), where no subfossil sites are known. Radiocarbon dates for subfossil lemur remains range from approximately 26,000 years BP (for Megaladapis in northern Madagascar at the Ankarana Massif) to around 500 years BP (for Palaeopropithecus in the southwest). Characteristics All of the extinct subfossil lemurs, including the smallest species (Pachylemur, Mesopropithecus, and the giant aye-aye), were larger than the lemur species alive today. The largest species were among the largest primates ever to have evolved. Due to their larger size, the extinct subfossil lemurs have been compared to large-bodied anthropoids (monkeys and apes), yet they more closely resemble the small-bodied lemurs. Like other lemurs, the subfossil lemurs did not exhibit appreciable differences in body or canine tooth size between males and females (sexual dimorphism). This suggests