Is There a Middle Stage of Evolution of the Leather Back Turtle?

So we have seven species, as i said, and six of them all belong to the hide top turtles. And then we have the leather back turtles, which are their own lineage. Leather bags actually look a lot more likethe, you know, the the older agis a swar, because they have a reduced carapase. So from the seven i have seen in the wilds six, im missing the flatbacked turtle. That is really a, my last one that i'm missing. I do work mainly with the species that we have in costrika, where i'm based. But for my pg d, i really extensively worked on fritlac clays - olive