Phylogenetic Relationships among Modern Birds (Neornithes): Toward an Avian Tree of Life

Abstract Modern perceptions of the monophyly of avian higher taxa (modern birds, Neornithes) and their interrelationships are the legacy of systematic work undertaken in the 19th century. Before the introduction of an evolutionary worldview by Charles Darwin in 1859, taxonomists clustered taxa into groups using similarities that reflected a vision of how God might have organized the world at the time of Creation. Such was the case with the Quinerian system of avian classification devised by Macleay (1819–1821) in which groups and subgroups of five were recognized, or of Strickland (1841) or Wallace (1856) in which affinities were graphed as unrooted networks (see O’Hara 1988). After Darwin, this worldview changed. For those comparative biologists struggling to make sense of Earth’s biotic diversity in naturalistic terms, Darwinism provided a framework for organizing similarities and differences hierarchically, as a pattern of ancestry and descent. The search for the Tree of Life was launched, and it did not take long for the structure of avian relationships to be addressed. The first to do so was no less a figure than Thomas Henry Huxley (1867), who produced an important and influential paper on avian classification that was explicitly evolutionary. 1868).