FUNCTIONAL COMPONENTS VERSUS MECHANICAL UNITS IN DESCRIPTIVE MORPHOLOGY

The concept of functional components was initially proposed by van der Klaauw ('45, '52) to indicate overlap of functional influences particularly in mammalian skulls; his analysis marked a departure from the study of single characters to that of function‐modified systems. A very similar set of terms is now coming into vogue to describe the mechanically separable components of highly kinetic fish, amphibian and reptilian skulls. In these cases the term functional unit often pertains only to the musculo‐skeletal system and is utilized during the process of description; it is often applied before a complete functional analysis has been carried out. Yet, any structure tends to be affected by the influence of multiple functions, and any function will almost certainly affect multiple characteristics of the animal. Since functional components overlap, the term should not be used to label an essentially topographical dissection of the animal. It cannot be expected that each loosely connected component of a kinetic skull subserves as a single “function,” and that this function does not overlap onto other units. It is suggested that the term mechanical unit be substituted as a label for the mechanical sub‐divisions often utilized to organize descriptions. The concept of functional units in the original sense then remains available as an analytical tool. Copyright © 1969 Wiley‐Liss, Inc.