Cardinalidae
Systematics

Traditionally, members of this group were classified as a tribe of the finch family Fringillidae (Cardinalini), characterized by heavy, conical, seed-crushing bills. The group consisted of the genera Pheucticus, Parkerthraustes, Saltator, Spiza, Cyanocompsa, Cyanoloxia, Porphyrospiza, Passerina, Caryothraustes, Periporphyrus, and Cardinalis. The issue that taxonomists had faced was that there were no unifying morphological traits that were in agreement for various studies. In 2007, a mitochondrial DNA study by Klicka, Burns and Spellman sampling all of the aforementioned genera and 34 of the total 42 species, found that the genera Parkerthraustes, Saltator, and Porphyrospiza were not members of the cardinal-lineage, but instead are found throughout in the tanager-lineage (Thraupidae). Interestingly enough the genera classified as thraupids at the time, Piranga, Habia, Chlorothraupis, and Amaurospiza, are found to be part of cardinalid radiation. In addition the genus Granatellus, originally classified as a parulid warbler, are also found to be part of Cardinalidae. The study found that with this new relationship Cardinalidae can be classified into five subgroups, which have been supported by subsequent studies. The five subclades consists of the Habia lineage (Habia and Chlorothraupis), the “masked” lineage (Piranga, Caryothraustes, Periporphyrus, Rhodothraupis, and Cardinalis), the Granatellus lineage, the “blue” lineage (Cyanocompsa, Amaurospiza, Cyanoloxia, Passerina, and Spiza), and the Pheucticus lineage. These subclades and membership of these genera have been widely supported in subsequent studies. A 2021 paper by Guallar et al. based on the preformative molting pattern of cardinalids suggested the ancestor of this group was a forest-dwelling bird that dispersed into open habitats on numerous occasions.

The cardinalids are part of a larger grouping of American endemic songbirds, Emberizoidea, which also includes the aforementioned thraupids and parulids, as well as icterids (New World blackbirds), passerellids (New World sparrows), and several families that contain one or a couple of genera. Several studies have placed cardinalids as either the sister group to Thraupidae, Mitrospingidae (a small family whose genera were formerly classified as thraupids), or the sister to a clade containing thraupids and mitrospingids. At least one study suggested that cardinalids could treated as a subfamily of Thraupidae.
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