Anatomy of the hand and arm in Daubentonia madagascariensis : a functional and phylogenetic outlook.

The aye-aye (Daubentonia madagascariensis) is easily the most enigmatic of living primates. It sports a unique combination of derived characters, including continuously growing incisors, functional claws, the largest hand of any primate and a highly modified middle finger. The specialised middle finger is no longer used in locomotion and serves as a probe-like instrument for investigating, locating and extracting xylophagous (wood-boring) larvae as well as other food items. Its phalanges can be moved both at great speed and independently of each other. The present study reports on dissections of the forelimbs of two individuals of D. madagascariensis and one specimen each of Lemur catta and Cercopithecus cephus. Derived characters of the forelimb musculature in Daubentonia are interpreted within the context of its distinct locomotor and foraging adaptations. The primary adaptations underlying speed and mobility in the third manual digit of Daubentonia are found in the intrinsic hand musculature and notably in the arrangement of the dorsal aponeurosis. Implications for the interpretation of suggested convergences between the aye-aye, the diprotodont marsupial Dactylopsila palpator and the early Tertiary apatemyid genus Heterohyus are discussed.