Li, Fraser, Rieppel and Wu 2018
introduce Eorhynchochelys sinensis (Figs. 1,2), which they describe in their headline as ‘a Triassic stem turtle’ and in their abstract as ‘a Triassic turtle.’ Unfortunately, Eorhynchochelys is not related to turtles. Instead it is a spectacular giant eunotosaur (sister to Eunotosaurus).
The problem is, once again, taxon exclusion.
Li et al. employed far too few taxa (Fig. 3) and no pertinent turtle ancestor taxa (see Fig. 4).
We know exactly from which taxa turtles arise.
In the large reptile tree (LRT, 1271 taxa, Fig. 4): 1) hard shell turtles arise from the small, horned pareiasaur, Elginia. The basalmost hard shell turtle is Niolamia, not Proganochelys. 2) soft shell turtles arise from the small, horned pareiasaurs, Sclerosaurus and Arganaceras. The basalmost soft shell turtle is Odontochelys. None of these taxa have temporal fenestrae. We looked at turtle origins earlier here. Turtle origins were published online in the form of a manuscript earlier here.
Pappochelys nests with basal placodonts. Eunotosaurus nests with the caseid clade, close to Acleistorhinus and Australothyris, all taxa with a lateral temporal fenestra. Li et al. suggested that this lateral temporal fenestra indicated that turtles were diapsids. That has been falsified by the LRT which shows that turtles never had temporal fenestra all the way back to Devonian tetrapods.
Eorhynchochelys sinensis (Li et al. 2018; Late Triassic) was considered the earliest known stem turtle with a toothless beak, but here nests as a giant aquatic eunotosaur with tiny premaxillary teeth. In size and overall build it converges with Cotylorhynchus.
Li C, Fraser NC, Rieppel O and Wu X-C 2018. A Triassic stem turtle with an edentulous beak. Nature 560:476–479.