In skeletal muscle development, the myogenic regulatory factors myf5 and myoD play redundant roles in the specification and maintenance of myoblasts, whereas myf6 has a downstream role in differentiating myocytes and myofibers. It is not clear whether the redundancy between myf5 and myoD is within the same cell lineage or between distinct lineages. Using lineage tracing and conditional cell ablation in mice, we demonstrate the existence of two distinct lineages in myogenesis: a myf5 lineage and a myf5-independent lineage. Ablating the myf5 lineage is compatible with myogenesis sustained by myf5-independent, myoD-expressing myoblasts, whereas ablation of the myf6 lineage leads to an absence of all differentiated myofibers, although early myogenesis appears to be unaffected. We also demonstrate here the existence of a significant myf5 lineage within ribs that has an important role in rib development, suggested by severe rib defects upon ablating the myf5 lineage.