History of the evolution of trappin genes in mammals. Phylogeny of mammalian species with the time scale was generated based on the works by Kumar and Hedges , Hasegawa et al. , Nishihara et al. , Hallstrom and Janke , and Arnason et al. . Ranges of the estimated dates for gene duplications are indicated by open boxes. Bayesian estimations of duplications using the nucleotide and the amino acid sequences of trappin genes are indicated by arrows and arrow heads, respectively. The dates of duplication estimated by MEGA software using single reference point are indicated by asterisks. The dates of duplications individually estimated by MEGA software for each species are indicated by double asterisks. Mya, million years ago.