Now turtles are diphyletic and finally make sense

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.

Figure 1. New cladogram of turtle systematics. Note the separation of soft shell turtles with orbits visible in dorsal view from domed hard shell turtles with laterally oriented orbits here.

Figure 1. New cladogram of turtle systematics. Note the separation of soft shell turtles with orbits visible in dorsal view from domed hard shell turtles with laterally oriented orbits here.

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.

Fig. 2. Ocepecephalon, the siphoning turtle. Originally the long dorsal rostrum bone was considered a premaxilla, but comparisons to sister taxa, like Trionyx, indicate it is an anterior nasal separated from the posterior nasal by a new naris, unlike that of any other turtle or tetrapod.

Fig. 2. Ocepecephalon, the siphoning turtle. Originally the long dorsal rostrum bone was considered a premaxilla, but comparisons to sister taxa, like Trionyx, indicate it is an anterior nasal separated from the posterior nasal by a new naris, unlike that of any other turtle or tetrapod. The naris and jaw opening are one here as the tiny premaxilla found in Trinoxy is completely absent here. The ectopteryogoids appear be broken here, but lacking a connection to the cheek may be yet another autapomorphy. New skull bone identities are labeled here.

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.

Figure 3. Dorsal views of bolosaur, diadectid, pareiasaur, turtle and lanthanosuchian skulls. The disappearance of the turtle orbit in lateral view occurs only in hard shell turtles.

Figure 3. Dorsal views of bolosaur, diadectid, pareiasaur, turtle and lanthanosuchian skulls. The disappearance of the turtle orbit in lateral view occurs only in hard shell turtles. Now the gradual accumulation of character traits is even more gradual. 

Correcting mistakes
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.

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