Nycteroleteridae

Nycteroleteridae is sometimes considered a sister group to the Pareiasauridae, but Bayesian inference suggests that it was in fact paraphyletic, with Rhipaeosaurus a basal member of the Pareiasauridae and other members of the Nycteroleteridae as outgroups. This is supported by the appearance of Rhipaeosaurus' skull and teeth - it had tricuspid teeth and multiple horns on the skull, resembling a pareiasaur but smaller and with a longer tail. For this reason it is often seen as intermediate between more primitive nycteroleterids and more advanced pareiasaurids such as Scutosaurus.[2]

• Subfamily † Nycteroleterinae
  • †Nycteroleter
  • †Emeroleter
• Unassigned subfamily
  • †Bashkyroleter
    • † Bashykroleter mesensis
  • †Macroleter
  • †Rhipaeosaurus

As discussed above, Nycteroleteridae technically includes all pareiasaurs as well as the five given genera. Within the five genera mentioned, there seems to be a smooth gradient of form from Macroleter to Rhipaeosaurus. Where Macroleter has no horns, Emeroleter has a few small horns, and Rhipaeosaurus' horns are quite large.[2]

However, there are some characteristic features of the Nycteroleteridae. They have a deeply incised otic notch, postparietal bones that enter the pineal opening, regular circular pits in the skull, and a row of palatal teeth from the interpterygoid vacuity to the edge of the choana.[2]

Examination of the nycteroleterids' middle ear bones and comparison with living amniotes showed that they probably had efficient impedance-matching hearing. This suggests that they may have been active at night or in dim-light environments. They are thought to have been carnivorous or insectivorous, but Rhipaeosaurus may have been an omnivore.[2]