The phylogenomic forest of bird trees contains a hard polytomy at the root of Neoaves

Abstract

Birds have arguably been the most intensely studied animal group for their phylogenetic relationships. However, the recent advent of genome-scale phylogenomics has made the forest of bird phylogenies even more complex and confusing. Here, in this perspective piece, I show that most parts of the avian Tree of Life are now firmly established as reproducible phylogenetic hypotheses. This is to the exception of the deepest relationships among Neoaves. Using phylogenetic networks and simulations, I argue that the very onset of the super-rapid neoavian radiation is irresolvable because of eight near-simultaneous speciation events. Such a hard polytomy of nine taxa translates into 2 027 025 possible rooted bifurcating trees. Accordingly, recent genome-scale phylogenies show extremely complex conflicts in this (and only this) part of the avian Tree of Life. I predict that the upcoming years of avian phylogenomics will witness many more, highly conflicting tree topologies regarding the early neoavian polytomy. I further caution against bootstrapping in the era of genomics and suggest to instead use reproducibility (e.g. independent methods or data types) as support for phylogenetic hypotheses. The early neoavian polytomy coincides with the Cretaceous–Paleogene (K-Pg) mass extinction and is, to my knowledge, the first empirical example of a hard polytomy.