PhyloCode in the context of "International Code of Zoological Nomenclature"

In biological taxonomy, taxonomic rank (which some authors prefer to call nomenclatural rank because ranking is part of nomenclature rather than taxonomy proper, according to some definitions of these terms) is the relative or absolute level of a group of organisms (a taxon) in a hierarchy that reflects evolutionary relationships. Thus, the most inclusive clades (such as Eukarya and Animalia) have the highest ranks, whereas the least inclusive ones (such as Homo sapiens or Bufo bufo) have the lowest ranks. Ranks can be either relative and be denoted by an indented taxonomy in which the level of indentation reflects the rank, or absolute, in which various terms, such as species, genus, family, order, class, phylum, kingdom, and domain designate rank. This page emphasizes absolute ranks and the rank-based codes (the Zoological Code, the Botanical Code, the Code for Cultivated Plants, the Prokaryotic Code, and the Code for Viruses) require them. However, absolute ranks are not required in all nomenclatural systems for taxonomists; for instance, the PhyloCode, the code of phylogenetic nomenclature, does not require absolute ranks.

Taxa are hierarchical groups of organisms, and their ranks describes their position in this hierarchy. High-ranking taxa (e.g. those considered to be domains or kingdoms, for instance) include more sub-taxa than low-ranking taxa (e.g. those considered genera, species or subspecies). The rank of these taxa reflects inheritance of traits or molecular features from common ancestors. The name of any species and genus are basic; which means that to identify a particular organism, it is usually not necessary to specify names at ranks other than these first two, within a set of taxa covered by a given rank-based code. However, this is not true globally because most rank-based codes are independent from each other, so there are many inter-code homonyms (the same name used for different organisms, often for an animal and for a taxon covered by the botanical code). For this reason, attempts were made at creating a BioCode that would regulate all taxon names, but this attempt has so far failed because of firmly entrenched traditions in each community.

Ornithurae (meaning "bird tails" in Greek) is a natural group that includes modern birds and their very close relatives such as the ichthyornithines and the hesperornithines. This clade is defined in the PhyloCode by Juan Benito and colleagues in 2022 as "the smallest clade containing Ichthyornis dispar, Hesperornis regalis, and Vultur gryphus".

Otidimorphae is a clade of birds that contains the orders Cuculiformes (cuckoos), Musophagiformes (turacos), and Otidiformes (bustards) identified in 2014 by genome analysis. George Sangster and colleagues in 2022 named the clade uniting turacos and bustards as Musophagotides, defining it in the PhyloCode as "the least inclusive crown clade containing Otis tarda and Musophaga violacea, but not Grus grus or Mesitornis variegatus".

While the bustards seem to be related to the turacos, other genetic studies have found the cuckoos to be closer to the bustards than the turacos are.

Phylogenetic nomenclature is a method of nomenclature for taxa in biology that uses phylogenetic definitions for taxon names. This contrasts with the traditional method, by which taxon names are defined by a type, which can be a specimen or a taxon of lower rank, and a description in words. Phylogenetic nomenclature is regulated currently by the International Code of Phylogenetic Nomenclature (PhyloCode).

Neoaves is a clade that consists of all modern birds (Neornithes or Aves) with the exception of Palaeognathae (ratites and kin) and Galloanserae (ducks, chickens and kin). This group is defined in the PhyloCode by George Sangster and colleagues in 2022 as "the most inclusive crown clade containing Passer domesticus, but not Gallus gallus". Almost 95% of the roughly 10,000 known species of extant birds belong to the Neoaves.

The early diversification of the various neoavian groups occurred very rapidly around the Cretaceous–Paleogene extinction event, and attempts to resolve their relationships with each other have resulted initially in much controversy.

Telluraves, also known as land birds or core landbirds is a recently defined clade of birds defined by their arboreality. Based on most recent genetic studies, the clade unites a variety of bird groups, including the australavians (passerines, parrots, seriemas, and falcons) as well as the afroavians (including the Accipitrimorphae – eagles, hawks, buzzards, vultures etc. – owls and woodpeckers, among others). This grouping was defined in the PhyloCode by George Sangster and colleagues in 2022 as "the least inclusive crown clade containing Accipiter nisus and Passer domesticus". They appear to be the sister group of the Phaethoquornithes.

Based on phylogenetic relationships among lineages of the Afroaves and the Australaves, it has been suggested that the last common ancestor of all Telluraves may have been an apex predator, and possibly also a bird of prey. Other researchers are skeptical of this assessment, citing the herbivorous cariamiform Strigogyps as evidence to the contrary.

The International Society for Phylogenetic Nomenclature was established to encourage and facilitate the development and use of, and communication about, phylogenetic nomenclature. It organizes periodic scientific meetings and is overseeing the completion and implementation of the PhyloCode.

Phylogenetic nomenclature (sometimes called cladistic nomenclature) is a method of nomenclature for taxa in biology that uses phylogenetic definitions for taxon names. Phylogenetic nomenclature assigns names to clades, groups consisting solely of an ancestor and all its descendants. This contrasts with the traditional method, by which taxon names are defined by a type, which can be a specimen or a taxon of lower rank, and a description in words. Phylogenetic nomenclature is regulated currently by the International Code of Phylogenetic Nomenclature (PhyloCode).