However careful the techniques of data collection and however detailed and complicated the methods of analysis, new insights into morphology cannot be expected if we do not take into account the fact that biological shapes exist within the limits of biological functions. Accordingly, in initial studies of shape, some information is needed about those aspects of the behavior of animals that have implications for the anatomical shapes concerned.
At one extreme, it might be thought that we require a relatively complete recognition of the detailed behaviors of which animals are capable. With the present status of research, this large gap in our knowledge is gradually being filled, especially by workers utilizing new hypotheses, techniques, and methods of analysis. However, for the great majority of genera, it will be some time, if ever, before all information can be garnered.
For instance, exhaustive study of the total locomotor pattern of a primate troop pertains to ecology and social behavior. It includes a whole range of data about environmental variables such as the topography of the general locality, the more detailed architectural features of the microniche (e.g., the shape, surface features, dendritic patterns, and strengths of tree branches), and about temporal changes such as seasonal flooding or foliage succession in vegetation. Direct information about locomotion should undoubtedly include feeding, resting, and sleeping postures; varieties of gaits; the duration, size, and frequency of leaps; the contexts in which alternative structures for locomotor patterns are used or avoided; the ontogeny of locomotor development; and so on. In all these and still other parameters, differences between troops should be estimated from the range of the whole species. Clearly the above series of studies could require a lifetime's commitment to even a single group. A reminder of the total number of currently recognized extant primate genera—59 according to Simpson (1945)—suggests the virtual impossibility of providing such data for evolutionary comparisons throughout the order.
At the other extreme, however, it is obviously inadequate to utilize concepts of function within behavior that relate to such broad and (especially within the primates) almost meaningless terms as "terrestrial" and "arboreal" when applied to entire locomotor modes.
Given the impossibility of obtaining the former detailed answer and the overly simplistic nature of the latter generalization, can we define practicable intermediates? What elements of the behavioral structure as it is now known are of most relevance in the understanding of morphology? The answers to such questions are likely to differ according to the nature of the behaviors, the particular animals, and the anatomical regions involved.
Thus, for living forms, lines of argument can be followed from behavior in the field to detailed morphology in the laboratory. In considering parts of the postcranial skeleton, major steps in such an argument are those shown in figure 12.