 Passeriformes

Passeriformes is the order of birds commonly called passerines or perching birds. Its major living branches include Acanthisittidae, the New Zealand wrens; Tyranni, the suboscines; and Passeri, the songbirds. Thus songbirds form an important branch within Passeriformes, rather than being an exact synonym for the entire order.^[ref]

The group illustrates how evolutionary histories are tested with independent kinds of evidence. A 2019 study analyzed 4060 nuclear DNA regions across 137 passerine families and used 13 fossils to calibrate the resulting phylogenetic tree. DNA comparisons estimate relationships and relative amounts of change; a fossil supplies an age constraint, rather than a complete date label for every branch.^[ref]

An illustrative consequence is that two visually similar birds need not be closest relatives: similar ways of feeding or moving can favor similar shapes. Conversely, related branches can evolve very different appearances. A well-sampled phylogenetic tree lets investigators ask whether a repeated feature was inherited once or arose independently, while making explicit which taxa and genes were compared. The 2019 reconstruction tested explanations for diversification instead of assuming that a rise in global temperature must automatically produce a matching rise in speciation.