Turtle carapaces, from species both extinct and extant; the black lines indicate bones, the gray lines are for scutes. What immediately struck me is that Chelodina oblonga appears to lack neural bones (running down the middle), however they are present, being encased by the costals. Early turtles (Proganochelys, Proterochersis, Kayentachelys, Plesiochelys) had incredibly wide vertebral scutes (also running down the middle) and apparently narrow ones evolved four separate times. And yes, the softshell (Amyda) is just a total freak.
Joyce, W. (2010) Phylogenetic Relationships of Mesozoic Turtles. Bulletin of the Peabody Museum of Natural History 48(1) 3–102.