Phylogenetic relationships among modern birds (Neornithes): towards an avian tree of life

Modem perceptions of the inonophyly of avian higher taxa {modern birds, Neomiihes) and their interrelationships are the legacy uf systematic work undertaken in the 19th century. Before Llie imroduttion of an evolutionary wo rid view by Charles Darwin in 1859, taxonomists clustered laxa into groups using similarities that reflected a vision of how God might have organized ilic world ai 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 hiotic diversity in naturalistic terms, Darwinism provided a framework for organizing similarities and differences hierarchically, as a pattern of aneestry 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 firsi 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, tt was also Huxley who provided the first strong argument that birds were related to dinosaurs (Huxley 1868), Huxley was particularly influential in England and was read widely across Europe, but the 'father of phylogeneiics" and phylogenetic "tree-thinking" was clearly Ernst Haeckel, Darwin's conceptual framework had galvanized Haeckel, and wfithin a few short years after Origin and a year before Huxley's seminal paper, he produced the monumental Generelle Morphola^c der Organismen•the first com]5rehensive depiction of the Tree of Life (Haeckel 1866). Haeckel's interests were primarily with invertebrates, but one of his students was to have a singular impact on systematic ornithology that lasted more than 125 years. In 1888 Max Furbringe r published his massive (1751 pages, 30 plates) two-volume tome on the morjjhology and systematics of birds. Showing his classical training with Haeckel and the comparative anatomist Carl Gegenbaur, Furbringer meticulously buili the first avian Tree of Life• including front and hind views of the tree and cross sections at different levels in time. The vastness of his morphological descriptions and comparisons, and the scope of his vision, established his conception of relationships as the dominant viewpoint within systematic ornithology. All classifications that followed can fairly be said to be variations on Furbringer's theme. Such was the magnitude of his insights. Indeed, as Stresemann (1959: 270) noted: