Figure 1.
Major amniote lineages and sex chromosome origins. The silhouettes indicate representative species for each group. Ages of main speciation events obtained from TimeTree (www.timetree.org) are indicated (millions of years ago, mya). Arrows indicate previously estimated ages of sex systems origins in amniotes (Cortez et al. 2014) and the age of the Anolis XY system as estimated in this study (see main text and Supplemental Fig. S1). Note that the age of the emergence of the snake ZW system and Pogona ZW system are not precisely known (see main text). Lineages for which RNA-seq data were generated in this study are marked by an asterisk.
