Comparative Odontometric Scaling in Two South American Tamarin Species: Saguinus oedipus oedipus and Saguinus fuscicollis illigeri (Callitrichinae, Cebidae)

Tamarins (Genus Saguinus) are small-bodied, arboreal monkeys found in the jungles and rain forests of South America. They belong to the subfamily Callitrichinae, and differ morphologically from other South American monkeys (belonging to the subfamily Cebinae) in a number of respects. The phylogenetic status of the Callitrichinae, relative to the Cebinae, has been the subject of much recent debate.

Previous research involving tamarins has involved a number of a priori assumptions and generalizations. There is a tendency to regard the tamarins as morphologically, behaviorally, and ecologically homogenous. A recent increase in the frequency and quality of studies involving tamarins has led to a questioning of many of these assumptions.

The purpose of this study was to document size and shape variation in the dentitions of two tamarin species: Saguinus Oedipus Oedipus and Saguinus fuscicollis illigeri. The sample included 62 illigeri (30 males and 32 females) and 61 Oedipus (32 males and 29 females). In the course of the analysis, two null hypotheses were tested. The first was that neither species would show any sexual dimorphism in tooth size, as evinced by the maximum diameters of the teeth. Sex comparisons of tooth size variation were also examined by observing the logged-value variances of the maximum tooth diameters. It was concluded that very little sexual dimorphism exists in the dentitions of the two species. The sexes of both species were therefore pooled in the subsequent species comparisons.

The second null hypothesis was that the dentitions of the species would show the same patterns of size related proportional (allometric) variation.

Interspecific studies of dental allometry frequently compare tooth size to an independent measure of body size, such as body mass. Body mass data were available for the sample, but few significant correlations between tooth size and body mass were found. As an alternative, intraspecific patterns of "internal" scaling variation were compared. Two methods of comparison were used: reduced major axis (RMA) regression and principal components analysis. It was found that individual tooth shape variation appears to be fairly independent of tooth size in both species. When tooth areas were examined, however, relative tooth areas and tooth size were found to be more strongly correlated. Within morphogenetic fields, comparisons of tooth areas conformed to the null hypothesis. When summed tooth areas were examined, the null hypothesis was rejected. The most striking species differences occurred in the relationships between the relative sizes of the premolars and molars, in which geometric dissociations were found.

The underlying causes of intraspecific dental scaling variation are still unknown and it is uncertain whether these patterns of variation serve any functional purpose. An alternative explanation of intraspecific variation might involve individual variation in the onset, rate, and duration of dental development. In any case, the phenomenon of intraspecific, "internal" dental scaling is recognized as a potentially valuable subject for further study.