Figure Legend
Figure 1. A theoretical evolutionary approach to moult in birds from reptiles, using the four moult strategies defined by Howell et al. (2003; see also Howell 2010). The phylogenetic tree is based primarily on that of del Hoyo & Collar (2014, 2016) with some revisions to reflect recent systematic advancements (see Supporting information file for the use of this tree during times of phylogenetic flux). The four strategies are Simple Basic (SBS; no preformative or prealternate moults), Complex Basic (CBS; a preformative moult but no prealternate moults), Simple Alternate (SAS; a single moult in the first cycle and prealternate moults in later cycles), and Complex Alternate (CAS; a preformative moult in the first cycle and prealternate moults in all cycles). Here we propose that both prebasic and preformative moults, and hence the Complex Basic Strategy (purple lineages in the figure), are ancestral to all modern birds, although further study is needed on when preformative moults evolved in primitive avian taxa or reptiles ancestral to birds. Prealternate (and presupplemental) moults have evolved many times along different lineages and should not be considered homologous. See Supporting information file for an expanded version of this phylogenetic tree (Fig. S1) along with detailed explanation and discussion.