There’s a new YouTube video on turtle origins.
have been arguing for decades about the origin of turtles. Unfortunately, they have been promoting unrelated taxa (Eunotosaurus and Pappochelys) while avoiding the verified sisters. Meiolania is a basal turtle with horns. Apparently it is more primitive than Proganochelys and Odontochelys despite its late appearance in the fossil record. Elginia is known only from a toothed and horned skull. We don’t know if it had a plastron and carapace. It was not a turtle unless it had a shell. Currently Elginia nests just outside of the turtle clade in the large reptile tree at http://www.reptileevolution.com. Sclerosaurus, Arganaceras and a few pareiasaurs, all without shells or broad ribs, are successively more distant relatives.
Adding to the problems of turtle origins, |
several temporal bones in turtles have been traditionally mislabeled. Here those misidentifications are corrected. Turtles now nest in a large gamut cladogram (572 taxa) with sisters and more distant relatives that document a gradual accumulation of turtle traits.
Other turtle sister candidates
are also examined, including Eunotosaurus and Pappochelys. The former converged with turtles as it had only a few very broad, turtle-like dorsal ribs. The latter was a basal placodont, not far from other placodonts that also developed a protective shell.
aligns turtles with archosaurs in some molecule studies, but no morphological studies do the same. That’s a problem still awaiting a solution.