Now this is an interesting beast. It’s a 220 million year old fossil from China of an animal that is distinctly turtle-like. Here’s a look at its dorsal side:
Notice in the skull: it's got teeth, not just a beak like modern turtles. The back is also odd, for a turtle. The ribs are flattened and broadened, but…no shell! It's a turtle without a shell!
Flip it over. There's another specimen, and we can look down on its ventral side, and there it is — a plastron, or the belly armor.
So, what we have here is a long-legged, toothed reptile with an elongate body, and it also has a plastron like a turtle, and hints in the bony structure of the spine of the carapace-to-be. It also fits perfectly with the embryology: modern turtles form the plastron first, and the carapace second. This is a _beautiful_ transitional form. I'd love to have some swimming in the streams near me. And here's a reconstruction of what they would have looked like, way back in the Triassic.
Li C, Wu X-C, Rieppel O, Wang L-T, Zhao L-J (2008) An ancestral turtle from the Late Triassic of southwestern China. Nature 456: 497-501.