Odontochelys semitestacea is a shell-less ancestor of the modern sea turtle. This species is a transitional form of amniote, a taxological group that includes mammals, reptiles, and birds. It lived in near shore waters, suggesting turtles evolved in the sea. It lived in the late Triassic period. Despite having expanded ribs that grow outwards, much like the shell of modern turtles, Odontochelys did not have ribs that were fanned apart and covering over its shoulder blades. This results in Odontochelys lacking a technical shell, but having ribs that, in life, would make it look very similar to a shelled turtle. This lack of a technical shell suggests it lived near the surface where it could easily protect itself from predators that attacked from below and lived in deeper seas.