Karyotypes and evolutionary relationships of trionychoid turtles.

Standard karyotypes of carettochelyid and trionychid turtles are similar. The pitted-shelled turtle, Carettochelys insculpta (2n=68), and three species of softshelled turtles, Trionyx spiniferus, T. ferox and T. sinensis (2n=66) were examined. Chromosomal banding patterns are the same among the species of Trionyx studied, but substantially different from non-trionychoid turtles. Karyotypic similarity supports previous morphological studies that indicate the families Carettochelyidae and Trionychidae are closely related or that both families are distantly related to other turtles.