Turtles first appeared on Earth in the Triassic, before the rise of the dinosaurs. The earliest turtle found in the fossil record is an odd-looking animal called Odontochelys semitestacea, discovered in China and dated to about 220 million years old. It appeared to have lived in water and had just a bottom shell (“semi” = half; “stacea” =shelled). Unlike modern turtles, it had a jaw full of teeth. In contrast, another fossil turtle, Proganochelys, dated to a bit later, resembles a modern turtle with a full shell (although it did have a few teeth still, in the middle of its mouth). Paleontologists are not sure whether land turtles evolved from aquatic half-shelled turtles like Odontochelys, or whether Odontochelys evolved from full-shelled ancestors living on land. They are searching for an ancestor to both Odontochelys and Proganochelys to help solve this mystery.