Earliest turtle with only a partial shell

The earliest known turtle with only a partial shell was Odontochelys semitestacea, which existed 220 million years ago during the late Triassic Period in what is now southwestern China. Unlike all subsequent turtles, it only possessed a ventral shell or plastron; it did not possess the familiar dorsal shell or carapace, thereby showing that during turtle evolution the plastron developed before the carapace. Instead, it merely sported neural plates and broadened ribs, like the ribs of modern-day turtle embryos before their true carapace begins to develop. Also, its beak still contained teeth, which no modern-day turtle possesses. It was formally described and named in 2008.

The earliest known turtle to possess a complete shell, i.e., consisting of both a plastron and a carapace, was Proganochelys quenstedti, which existed approximately 210 million years ago during the late Triassic. Various fossils from this species have been found in strata in Germany and Thailand.

It was formally described and named in 1887.