Feeding behavior, mastication, and tooth wear in the western tarsier (Tarsius bancanus)

Abstract

We assessed feeding and masticatory function in western tarsiers, Tarsius bancanus,from field study, from videotaped recordings of the feeding and chewing behavior of wild-caught animals in temporary captivity, from dissections of the muscles of mastication, and from scanning electron microscopic (SEM) examination of wear features of the teeth. Ingestion 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 possible a gape angle of 60–70‡. We observed two means of ingestion of grasshopper prey: ingestion by mastication, in which the postcanine teeth sever and reduce bites of the food as it is thrust into the mouth cavity, and repeated gape-shove sequences, during which the tarsier 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 reduced quickly,with relatively few powerful, crushing chews. The insect cuticle was not evenly comminuted during mastication. We observed a marked side-to-side grinding component in the normal chewing cycle of T. bancanuson 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 necessary to fracture thick chitinous exoskeletons of the scarabid beetles that form a substantial element of the western tarsier’s diet.