Lack of resolution in the animal phylogeny: Closely spaced cladogeneses or undetected systematic errors?

A recent phylogenomic study reported that the animal phylogeny was unresolved despite the use of 50 genes. This lack of resolution was interpreted as a positive signature of closely spaced cladogenetic events. Here, we propose that this lack of resolution is rather due to the mutual cancellation of the phylogenetic signal (historical) and the nonphylogenetic signal (due to systematic errors) that results from inadequate taxon sampling and/or model of sequence evolution. Starting with a data set of comparable size, we use 3 different strategies to reduce the nonphylogenetic signal: 1) increasing the number of species; 2) replacing a fast-evolving species by a slowly evolving one; and 3) using a better model of sequence evolution. In all cases, the phylogenetic resolution is markedly improved, in agreement with our hypothesis that the originally reported lack of resolution was artifactual.