Many genomic changes took place along the evolutionary lineage that gave rise to the Animal Kingdom. Recent research has revealed the role that co-option of old genes played during this transition, but the contribution of genomic novelty has not been fully assessed. Our analyses of a large genomic dataset using new phylogeneticallyaware tools revealed an increase of genomic novelty in the dawn of the Metazoa not seen before, and highlight 25 groups of highly retained novel genes with functions essential to metazoan biology.
