Phylogenetic relationship and sex determination systems in Gekkota (A), and phylogenetic relationships in Pygopodidae (B). A. Phylogenetic tree is referred to Vidal and Hedges . The sex determination systems are adopted from Gamble . The number of described species followed by the number of species with known sex determining mechanism is shown under each family. XY indicates clade contains species with male heterogamety, ZW indicates clade contains species with female heterogamety, TSD indicates clade contains species with temperature-dependent sex determination and GSD indicates clade contains species with genetic sex determination not associated with heteromorphic sex chromosomes. B. Phylogenetic trees of seven genera of Pygopodidae are adopted from Jennings et al. : left and Oliver and Sanders : right, respectively.