Updated May 10, 2016 with a new nesting of Nikksaurus with basal prodiapsids.
It’s hard to find data on Nikkasaurus,
a tiny basal prodiapsid without fangs. The only data I know comes from Ivahnenko (2000) in the form of a drawing or two (Fig. 1). Earlier we looked at just the skull of Nikkasaurus and how tiny it was, now nesting with Mycterosaurus at the base of the Prodiapsida.
Figure 1. Nikkasaurus and what little is known of its postcrania. Above, in situ. Below, tentative reconstruction. If anyone has a picture of the fossil itself, please send it.
The longer legs
that made prodiapsids special are seen here. No doubt this is a product of paedomorphy as the only other basal synapsid/diapsid juvenile I know of, baby Dimetrodon, also had longer legs than its adult counterpart. The difference here: the crus and antebrachium don’t appear to be very bowed between the tibia and fibula, as in the closest sister, Mycterosaurus.
Some basal prodiapsids
lose the primitive fang. Nikkasaurus is one of those.
References
Ivahnenko MF 2000. Cranial morphology and evolution of Permian Dinomorpha (Eotherapsida) of eastern Europe. Paleontological Journal 42(9):859-995. DOI: 10.1134/S0031030108090013
The Pterosaur Heresies 