INTRODUCTION TO COMPARATIVE ANATOMY

I. Comparative Anatomy (= Comparative Morphology)
   A. Similarities & differences in vertebrate form/structure.
      1. Comparison to illustrate functional & evolutionary themes underlying 
         similarities/differences.
      2. Comparison helps to formulate questions about structure.
         eg. homocercal tail vs. heterocercal tail
      3. Functional morphology = study of form coupled with function.

   B. Comparative analysis = tool
      1. Historical context:
         a. Evolutionary events (w/ respect to morphological units)
         b. Phylogeny
         c. Classification
      2. Non-historical context: extrapolative (info about some verts may tell us about 
         other verts.)  
         eg. effects of drugs; force produced by muscle

   C. Form and Function: look for explanations of vert. design by examining reasons for, 
      or the processes that produce, the structural plan of vertebrates.
      1. External environment exerts evolutionary pressures on anatomy (adaptation).
      2. Structure affects design via possibilities/limitations.
      3. Why don't any terrestrial vertebrates have wheels for locomotion?
      4. Evolution preserves favored structures.
      5. Focus on Kardong, p.15: "Why are there no flying elephants?"

II. Similarities
    A. Criteria:
       1. Ancestry
       2. Function
       3. Appearance

    B. Homology = similarity inherited from common ancestor.
       (serial homology = similarity of successively repeated parts in same organism.)
    C. Analogy = similarity due to necessity of function.
       1. Organisms may or may not share common ancestry.
       2. Indicates adaptation to similar environments or life styles.
    D. Homoplasy = structures just look alike.
       1. May or may not be homologous or analogous.
       2. May be due to chance.
    E. There may be overlapping between any two or all three of these types of similarity.

III. Morphological Significance
     A. Functional significance: how structure contributes to function of organism.
     B. Evolutionary significance: how is structure important in terms of evolution of verts.
        1. May be important step in transition.
        2. Pre-adaptation (predisposition):  structure or behavior possesses necessary form
           and function before the biological role arises; can do job before job is defined.
           a. Does not imply anticipation, planning, or innate evolutionary direction.
           b. If no role arises, selection may eliminate feature.