Tooth form and diet in ateline and alouattine primates; reflections on the comparative method

By identifying consistent relationships between mor­ phology and ecology across taxa, the comparative method allows the testin~ of ideas about adaptation and permits the reconstruction of behavIOr in extinct forms. The association between dental morphology and dietary adaptation is explored for ateline and alouattine ~rimates. Using allometrIC techniques and a criterion of subtraction' reveals that folivores (Alouatta, Brachyteles) have relatively small lower incisors and relatively well-developed molar shearing crests compared to frugi­ vores (Ateles, Lagothrix). The development of molar shear crests in the fossil alouattines of the genus Stirtonia is indicative of diets nearly as folivorous as in Alouatta. The existence of multiple adaptive solutions to a single selective pressure does not preclude usin~ the comparative method for predic­ tive purposes as long as the goal IS to infer behavior from morphology and not the reverse. Similarly, nonadaptive convergence does not invalidate the entire comparative method but only means that not all hypothesized relationships between morphology and behavior will have predictive power. Comparative hypotheses mar be tested at any taxonomic level for which there is measurable variatIOn in the traits to be examined. However, considering only independent evolutionary occurrences-rather than individual taxa-disregards trait mainte­ nance as a valid trial of a comparative hypothesis.