Dental, occlusal, and associated jaw morphology of the woolly spider monkey Brachyteles arachnoides are described in a functional and comparative context. The masticatory and digestive systems of this rare geographic isolate show a high order of concordance with homologous structures in the Alouattinae and differ in significant ways from the other Atelinae. Brachyteles is viewed as a facultative leaf-eater. These shared traits, many of a primitive nature, reflect common descent from a leaf-eating, brachiating proto-atelinine-alouattine ancestor. Lagothrix and Ateles are highly concordant in their masticatory characteristics, the form-functional attributes of which represent an evolutionary trend away from the primitive tooth form and transverse jaw functioning found in Brachyteles and Alouatta.
Morphological and developmental characteristics of the rhesus monkey nasopalatine duct system and associated primary palatal structures are described along with functional and phylogenetic considerations. Examination of five adult palates and coronal sections of 13 fetal palates together with dissections of a sixth adult specimen and of a 119-day-old fetal palate reveal that the lateral lobes of the tripartate incisive papilla cover clefts leading into the ducts. The ducts pierce the bony palate to enter the nasal fossae in proximity to the incisive suture. The ontogenetic stability of the duct path reflects the retention of ancient duct and primitive choanae relationships and functionally maintains an optimal oral odorant-to-receptor channel. Sixteen timed pregnancy specimens (35-100 days) provided histological material for documenting rostral nasopalatal development. Duct primordia, identified at 35 days, had by 40 days formed the medial duct walls (conjoined septum-papilla from the primary medial palatal component), the lateral duct walls (maxillary processes), and the rostral walls (fused maxillary-intermaxillary components). The caudal walls derive from the fusion of palatal shelves with the papilla (45 days), thus distinguishing primary and secondary fusion modes. Duct epithelial maturation occurs between 70 and 100 days. The absence of a vomeronasal system is attributed to reduction of olfaction in reproductive behavior, while the presence of the coevolved nasopalatine ducts is linked to the persistence of epiglottal-velar valving. The ducts serve as oral food-odor conduits in otherwise functionally separated respiratory and digestive tracts.
The form of the unworn male Cercopithecoid maxillary canine tooth (C') is effectively adapted for stabbing and slashing. Its essential features are maintained by wear against the mandibular canine ( C , ) and first premolar (Pa) teeth. The cusp tip of Ci is sharpened by reciprocal wear against C'. The distribution of apposing wear facets indicates that functional attrition results from honing activity largely distinct from mastication. Functional attrition also occurs in reduced form in fcmales and is produced within the masticatory excursive range. The significance of the "sectorial" form of Ps is analvzed. Its elongated mesiobuccal surface serves the dual purpose of honing the distal cutting edge of C' and functioning as a cutting block against which vegetation is stabilized and shredded by the cervical third of the distal cutting edge of C'. Behavioral aspects of honing are coyrelated with field observations linking tooth grinding with aggression, tension releasc, and communication. Parallel human behavior is cited and the suggestion is made that human tooth grinding with its highly charged emotional overtones is largely relict behavior that once had high survival value in a canine tooth honing context.
Permanent maxillary canine teeth (C1) are appreciably larger in males than in females in most nonhominid Anthropoidea. Mandibular canines (C1) and mandibular first premolars (P3), against which C1 are sharpened in honing behavior, reflect commensurate sexual dimorphism. These three teeth constitute the canine dental complex. The canine complex crown metrics of seven mature genetically female rhesus Macaques, androgenized by prenatal exposure to testosterone propionate, were compared with a control sample (N = 12) for evidence of masculinization. The C1 and C1 were measured for clinical crown lengths (L) and mesiodistal and buccolingual widths. The functionally significant and highly dimorphic honing dimensions (HD), which approximate the honing surfaces of P3, were noted. In t-test comparisons, the C1 L and P3 HD in androgenized monkeys were significantly larger than those of the control group (P less than 0.05). Identical results were obtained with White's nonparametric ranking technique. Standardized lateral skull radiographs showing earlier dental formative stages were available for five of the seven animals, and these were compared with radiographs of control skulls. The developing C1 were longer and wider than in the controls. This was not reflected in the crown metrics of mature animals because of marked dental attrition. We concluded that androgens can masculinize the female rhesus canine complex, if given during critical periods of prenatal development. We hypothesize that genes encoding the male canine complex are normally activated by endogenous fetal androgens during such critical periods.
Underbites or mandibular incisor protrusions are widely prevalent among Coloboid monkeys. The morphological basis of the trait is explored in two langur species differing with respect to its incidence. P. melalophus, characterized by a high occurrence of underbites, has mandibular incisors which are significantly wider than those of T. cristntus, the more "normative" occlusal group. No other statistically significant incisor metric differences are noted. Comparisons of convergent traits jn the Colobinae, Alouattinae, and Rurninantia supFort the contention that underbites are a herbivorous adaptation. The zoogeographic distribution of the trait in langurs is discussed in the context of evolutionary dynamics.
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