How turtle shells evolved... twice

Modern turtle shells are almost as diverse as the turtles themselves. Sea turtles have flatter, lighter shells for gliding through the water. Land-dwelling tortoises have domed shells that can slip free of predators' jaws. Leatherback turtles have shells without the ring of bone around the edge. So how did the shell evolve? Judy Cebra-Thomas explores the ancestry of the turtle. [Directed by Cabong Studios, narrated by Bethany Cutmore-Scott, music by Matheus Wittmann].