This corresponds to early embryonic stages of carapace formation in extant turtles, and shows that the turtle shell is not derived from a fusion of osteoderms.

• 但另一种理论认为是先形成腹甲，接著肋骨再自然发展并加宽，同时背骨也变成硬甲壳，让乌龟可以缩进去躲避掠食者。