These primitive cryptodires are most closely related to the Carettochelyidae of New Guinea and Australia. The oldest softshell fossil is from the late Jurassic. The recent revision of the phylogenetic arrangement proposed by Meylan has yet to gain universal acceptance and use, but it is generally supported by both morphological and molecular evidence. Two subfamilies are recognized: Trionychinae (without flexible flaps on plastron below hind limbs) and Cyclanorbinae (with flexible flaps on plastron below hind limbs).
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