Turtle systematics has changed for the better
Flattened softshell turtles are indeed different from domed hardshell turtles. The arose from separate, though closely related, non-shelled ancestors according to the latest data input and recovered from the large reptile tree (subset Fig. 1). The carapace and plastron in each turtle clade arose by convergence, based on present data. Earlier we looked at where other paleontologists have been looking for the ancestors of turtles.
I had it wrong earlier
And that’s okay as Science marches on. We build on past successes and mistakes made by both ourselves and others (see below). I saw a Red Flag (= a logical inconsistency, see below) and reexamined my data scores. New understandings popped up, like the absence of a premaxilla in Ocepecephalon and the coincident appearance of a new secondary naris high on the skull dividing the nasal bone (fused at its midline) in two (Figs. 2). That is very weird and may be unique for all tetrapods. A sister, Trionyx, has only a vestige of a premaxilla and no ascending process. So Ocepecephalon simply took it to the next level and completely lost the premaxilla — and perhaps most of the ectopterygoid.
This new tree topology for turtles solves the problem
of toothy Odontochelys appearing after the loss of teeth in ancestral taxa, as recovered by the old data with several incorrect scores. And this also solves the problem of soft-shell turtles with dorsally visible orbits, like Odontochelys, Trionyx and Ocepecephalon (Fig. 2), appearing after the orbits had already rotated to the lateral side of the skull in hardshell turtles derived from Elginia, Meiolania and Proganochely.
and seeking new insights are what ReptileEvolution.com and this blog are all about, whether I made the mistakes or others made the mistakes (usually a combination of the two). On a grander scale, that’s what Science is all about. It also feels good to solve persistent problems.
The .nex file is available on request, as always.