Fig. 1.

Recent phylogeny of turtles based on 14 nuclear genes, showing familial relationships. Solid lines indicate asynchronous anteroposterior rowing motions of forelimbs and hindlimbs for swimming (presumptive ancestral condition), dashed line indicates synchronous dorsoventral flapping motions of forelimbs for swimming in sea turtles (derived), and dotted line indicates swimming in Carettochelys insculpta (the only extant member of the family Carettochelyidae, and the only freshwater turtle species with forelimbs modified into flippers that swims using synchronous forelimb motions). The family Emydidae includes Trachemys scripta, Chelonioidea includes Caretta caretta and Trionychoidea includes Apalone ferox. Branch lengths do not reflect time since divergence. Time since divergence of focal lineages is indicated at nodes: 1=175 mya; 2=155 mya; 3=94 mya. Phylogeny is based on Barley et al. (Barley et al., 2010). Estimates of divergence times are based on Near et al. (Near et al., 2005).