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Chelidae: Chelids are characterized by unusually extensive emargination of the cheekbones so that only a parietal-squamosal bar remains. Quadratojugals and mesoplastra are absent, distinguishing chelids from pelomedusids. Key osteological features: cervical scute present; neurals reduced, 7 or fewer, absent in some; 9 plastral bones, mesoplastra absent; no quadratojugal or temporal arch; prefrontals not in contact; palatals separated by vomer; lower jaw usually slender and weak; neck incompletely retractile; 5th & 6th cervicals amphicoelous, none saddle-shaped; neck typically very long, retracted by 1 or 2 lateral bends; cervical scute usually present, absent in 1 genus |
