Microleter (Fig. 1) was described a few years ago (Tsuji et al. 2010) as an Early Permian parareptile (an invalid multiphyletic assembly of early reptiles). Tsuji et al. nested Microleter between millerettids and Acleistorhinus + Lanthanosuchus (another unnatural assembly).
Tsuji et al. used the matrix of Modesto et al. (2009) which was based on Mülller and Tsuki (2007) consisting of 30 taxa and 137 characters. Both numbers are too small. The analysis recovered six trees in which Microleter nested in an unresolved polygamy with Australothyris and Acleistorhinus + Lanthanosuchus at the base of the ‘ankyramorphan parareptiles’ (another unnatural assembly).
The large reptile tree (575 taxa, completely resolved) found Microleter nested between Delorhynchus and Eunotosaurus + Acleistorhinus. The clade Australothyris + Feeserpeton is the proximal outgroup. The caseasaurs and millerettids are more distant.
With insight Tsuji et al report, “As it is becoming increasingly clear, temporal fenestration is actually a common phenomenon among parareptiles, quite a departure for a group once termed Anapsida.”
Tsuji et al. include mesosaurs in their parareptilia and do not give them temporal fenestra. Oddly Tsuji et al nest Procolophon with Owenetta. Oddly they nest Eudibamus with Belebey. Oddly Tsuji et al nest Acleistorhinus with Lanthanosuchus, but not Eunotosaurus.They think the anapsid condition re-evolved in pareiasaurs. That’s not true. The ‘parareptile’ pseudoclade is a mess. It’s time for a thorough cleaning with more taxa.
the pterygoids produced a circular opening between them, as in Eunotosaurus, but not so exaggerated. Acleistorhinus does not have this trait. Here (Fig. 1), based on self-evident transfer techniques, the lateral temporal fenestra is reconstructed larger than Tsuji et al. drew it freehand. The lacrimal may not have contacted the naris according to the reconstruction where the maxilla contacts the nasal.
Linda A. Tsuji; Johannes Muller; Robert R. Reisz (2010). “Microleter mckinzieorum gen. et sp. nov. from the Lower Permian of Oklahoma: the basalmost parareptile from Laurasia”. Journal of Systematic Palaeontology 8 (2): 245–255.