The evolution of giant flightless neognath birds and novel phylogenetic relationships for extinct fowl (Aves, Galloanseres)

WORTHY, T.H.; LEE, M.S.Y.; DEGRANGE, F.J.; HANDLEY, W.D.

Queensland

Congreso; 16th Conference of Australasian Vertebrate Evolution, Palaeontology and Systematics (CAVEPS); 2017

The giant extinct dromornithids, gastornithids, and phorusrhacids include some of the most spectacular birds to have ever lived, with some giants exceeding 500kg. Spread widely on the globe and spanning some 60 Ma, the affinities and evolution of these and other related birds remains contentious due to widespread convergence and limited taxon sampling in phylogenetic analyses. We address these problems using both parsimony and tip-dated Bayesian approaches on an expansive taxon set (48 taxa, 290 characters) including key extinct flightless and flighted (e.g. Vegavis and lithornithids) forms, an extensive array of extant fowl (Galloanseres), representative Neoaves, and palaeognaths. The tip-dated Bayesian analyses recovered the most evolutionarily plausible trees, better overcoming homoplasy issues than parsimony analyses. The volant Paleogene Lithornithidae are recovered as stem palaeognaths, not sister to tinamous, thereby becoming candidates for the ancestral ratites. South America?s largest bird, Brontornis, is a Neoaves related to Cariamiformes, and therefore giant Galloanseres remain unknown from this continent. Within Galloanseres we recognise four basal clades, each with a Late Cretaceous Gondwanan origin. Ranked equally with Anseriformes and Galliformes, we identify a robust new clade (Gastornithiformes) for the giant flightless Dromornithidae (Australia) and Gastornithidae (Eurasia, North America). As for ratite palaeognaths, flight was lost and giant size attained multiple times. A fourth clade is represented by the Cretaceous Vegavis (Antarctica), which was robustly excluded from crown Anseriformes, redefining a crucial molecular calibration point. The presbyornithids Wilaru (Australia) and Presbyornis (Northern Hemisphere) are robustly found to be the sister group to Anatoidea (Anseranatidae + Anatidae), a relatively more basal position than hitherto recognised.