derived by descent from derived from ancestral fusion of derived from ancestral fusion of false RO:0002374 has_fused_element A has_fused_element B does not imply that A has_part some B: rather than A has_part some B', where B' that has some evolutionary relationship to B. has_fused_element has fused element x has_fused_element y iff: there exists some z : x has_part z, z homologous_to y, and y is a distinct element, the boundary between x and z is largely fiat