FEEDING-BEHAVIOR, MASTICATION, AND TOOTH WEAR IN THE WESTERN TARSIER (TARSIUS-BANCANUS)

We assessed feeding and masticatory function in western tarsiers, Tars ius bancanus, from field study, from videotaped recordings of the feed ing and chewing behavior of wild-caught animals in temporary captivity , from dissections of the muscles of mastication, and from scanning el ectron microscopic (SEM) examination of wear features of the teeth. In gestion of large items of animal prey is made possible by the animal's extremely wide gape. Anterior translation of the knob-like mandibular condyle in the anteroposteriorly elongated mandibular fossa makes pos sible a gape angle of 60-70-degrees. We observed two means of ingestio n of grasshopper prey: ingestion by mastication, in which the postcani ne teeth sever and reduce bites of the food as it is thrust into the m outh cavity, and repeated gape-shove sequences, during which the tarsi er pushed grasshoppers of large diameter into the anterior part of its mouth and attempted to sever a bite with its anterior teeth. Morsels were successfully severed after three to five such sequences, and redu ced quickly, with relatively few powerful, crushing chews. The insect cuticle was not evenly comminuted during mastication. We observed a ma rked side-to-side grinding component in the normal chewing cycle of T. bancanus on videotape and confirmed it by SEM. The main jaw adductors are bulky, long-fibered muscles that can accommodate wide grapes and still generate, at wide degrees of gape, the high occlusal pressures n ecessary to fracture thick chitinous exoskeletons of the scarabid beet les that form a substantial element of the western tarsier's diet.