Feathered dinosaurs, flying dinosaurs, crown dinosaurs, and the name “Aves”

The taxon name “Aves” is currently used for several different clades, a situation that violates the fundamental nomenclatural principle that, to minimize ambiguity, each taxon name should refer to a single taxon. To clarify this situation, we explore some general issues concerning the properties of the three classes of phylogenetic definitions, including: how names can be tied to clades through composition or characters; the relationships between “total” and “crown” compared to “stem” and “node” clades; how taxa can be referred to clades whose names are defined using different classes of phylogenetic definitions; perceived problems with apomorphy-based definitions; whether and in what senses taxon names have traditional meanings; and the consequences of restricting Aves to each one of the four clades to which it is most commonly applied. We then propose a taxonomy that resolves current nomenclatural ambiguity by using a different name for each of the clades that everyone wants to talk about—namely, those composed of bird-line archosaurs, the feathered dinosaurs, the flying dinosaurs, and the crown dinosaurs—instead of referring to all of them as “Aves.” Our proposed taxonomy also fixes the clade references for six additional names—“Carinatae,” “Ornithurae,” “Palaeognathae,” “Tinamidae,” “Ratitae” and “Neognathae”—that are no less than a century old, as well as two newer ones—“Galloanserae” and “Neoaves.”