Figure 4. Morphologic debt for polymorphic taxa when some taxa are fixed as ancestors. Colors and symbols as in Figure 3. Fixed ancestors are represented by thin black lines. 4.1) When a polymorphic taxon is fixed as an ancestor, and its direct descendant is not, then units of debt must be added for each state not observed in the descendant. If the fixed taxon's ancestor is not polymorphic, then units of debt must also be added for each state reconstructed in the ancestor. 4.2) If a monomorphic taxon is fixed as an ancestor, and its direct descendant is polymorphic, units of debt must be added for each state not observed in the fixed ancestor.