A recent paper
by Spindler, Falconnet and Fröbisch 2016 correctly reassigned two former haptodine synapsids to the base of the Caseasauria.
Datheosaurus macrourus (Schroeder 1904, Spindler, Falconnet and Fröbisch 2016, Artinskian, Early Permian, 285 mya) was a basal caseasaur, basal to Ennatosaurus and Casea and a sister to Eothyris, all derived from a sister to Eocasea and before that, Milleretta RC70. It was originally and later (Romer and Price 1940) considered a sister to Haptodus. At present the part and counterpart fossils have not been fully worked out.
Callibrachion gaudryi (Boule and Glangeaud, 1893b; Spindler, Falconnet and Fröbisch 2016) was similar and larger, but is less completely known.
Both of these taxa
were originally described over a hundred years ago and have not been studied much since then. Romer and Price (1940) evidently paid little attention to them and followed the earlier assignment to the haptodine synapsids. Please note that over a hundred years ago, when these taxa were first studied, there were very few other basal reptile specimens to compare them to, essentially just Mesosaurus and Protorosaurus. Other casesaurs first came to light in the late 1930s. It is good that they have been finally and correctly reassigned.
Spindler, Falconnet and Fröbisch 2016 follow tradition (without testing) and nest the Caseasauria at the base of the Synapsida. The large reptile tree tests more possibilities and provides more opportunities. It nests all caseasaurs with Feeserpeton, Australothyris, Acleistorhinus and Eunotosaurus derived from millerettids, like Milleretta RC70, among the new Lepidosauromorpha, not with the Synapsida. We looked at the mistaken nesting of caseasaurs several years ago here.
Spindler et al. note: “These new observations on Datheosaurus and Callibrachion provide new insights into the early diversification of caseasaurs, reflecting an evolutionary stage that lacks spatulate teeth and broadened phalanges that are typical for other caseid species. Along with Eocasea, the former ghost lineage to the late Pennsylvanian origin of Caseasauria is further closed. For the first time, the presence of basal caseasaurs in Europe is documented.Here, we re-describe Callibrachion gaudryi and Datheosaurus macrourus for the first time in detail. The specimens are too poorly preserved to allow their inclusion in a phylogenetic analysis. Nonetheless, their assignment to Caseasauria is robust, therefore we attempt to discuss the historical findings as well as caseasaurian phylogenetic and evolutionary trends.”
I found no problem
including the more complete Datheosaurus in phylogenetic analysis in the large reptile tree (now 630 taxa). It nested right about where Spindler, Falconnet and Fröbisch 2016 said it would.
Boule M and Glangeaud P 1893a. Le Callibrachion Gaudryi, nouveau reptile fossile du Permien d’Autun. Bulletin de la Société d’Histoire naturelle d’Autun 6: 199–215.
Romer AS and Price LI 1940. Review of the Pelycosauria. Geological Society of America Special Papers 28: 1-538.
Schroeder H 1904. Datheosaurus macrourus nov. gen. nov. sp. aus dem Rotliegenden von Neurode. Jahrbuch der Königlich Preußischen Geologischen Landesanstalt und Bergakademie 25 (2): 282–294. [reprint 1905]
Spindler F, Falconnet j and Fröbisch J 2016. Callibrachion and Datheosaurus, two historical and previously mistaken basal caseasaurian synapsids from Europe. Acta Palaeontologica Polonica 61: xx-xx. http://dx.doi.org/10.4202/app.00221.2015