The phylogenetic relationships between the vertebrate visual opsin lineages. A series of four duplication events produced the lws, sws1, sws2 and then rh1 and rh2 genes. The position of each branch on the spectrum portrays the approximate spectral sensitivity of each opsin group. Maximum absorbance value ranges (nm) are based on pigments reconstructed with 11-cis retinal. Values are taken from , figure adapted from .