Figure 1. The origin of the Dicynodontia from basal therapsids. Here Cutleria, Stenocybus, two unnamed taxa, Otsheria, Venjukovia, Eodicynodo and Dicynodon are shown in order along with the major trait that each portrays. Click to enlarge. Most basal synapsids are known from skulls. During the evolution of the dicynodonts, the tail became very short and the toes were shorter as well.
Earlier we looked at the origin of dicynodonts and dromasaurs separate from all other synapsids. Here (Fig. 1) are a selection of skulls that demonstrate the evolutionary origin of the very odd skull of Dicynodon, only one of many dicynodonts.
Wikipedia reports
“Dicynodontia is a taxon of anomodont therapsids or synapsids with beginnings in the mid-Permian, which were dominant in the Late Permian and continued throughout the Triassic, with a few possibly surviving into the Early Cretaceous. Dicynodonts were small to large herbivorous animals with two tusks, hence their name, which means ‘two dog tooth’. They are also the most successful and diverse of the non-mammalian therapsids, with over 70 genera known, varying from rat- to ox-sized.”
Wikipedia also reports
that dicynodonts nested between dinocephalians and gorgonopsians. That is not supported in the large reptile tree as both are quite derived and don’t take into account basal pre-dicynodont taxa.
You can see a number of therapsid skulls in evolutionary order here.
The Pterosaur Heresies 