Molecular evolution of khdrbs genes and the origin of vertebrate tripartite brain. The evolutionary relationships of metazoan and Vertebrata are based on our analyses above and recent phylogenomic analyses. Two red bars represent the 2R WGD events happening around the origin of vertebrate linage. The yellow one indicates teleost specific WGD event. Those blue rectangles represent the process of khdrbs gene duplication and diversification. The branch lengths are not proportional to the time of diversification.