Pareiasaurs include some of the largest and most dramatic of Late Paleozoic tetrapods. Though some are small, others got as large as cows. Recently, a somewhat obscure group of Russian forms known as the nycterolyterids have been suggested as close relatives of pareiasaurs, and Tsuji and Muller have brought them together in the larger taxon known as Pareiasauromorpha: Reptilia Eureptilia Parareptilia Ankyromorpha Pareiasauromorpha “Nycteroleteridae” Pareiasauridae
NYCTEROLETER PARAREPTILES The nycteroleters have been, until relatively recently, a somewhat obscure group of primarily Russian fORms form the middle to upper Permian. They have been obscure, in part, due to their documentation primarily in Cyrillic by Russian paleontologists. This has been ameliorated recently by the careful [re]descriptions of Macroleter and Emeroleter by Tsuji and colleagues.
If we look at recent global analyses of Parareptilia, the nycteroleters have been sometimes been considered a monophyletic group, and sometimes not. When considered monophyletic, the in- group relationships still have not been clear, and about the best we can say is that nycteroleters are more closely related tone another than anything else, but the intra-relationships remain largely unresolved. Note that in the following phylogeny from Tsuji et al (2012): The nycteroleters are considered a monophyletic group But, with the exception of Macroleter, Tsuji et al could only interpret the remaining five genera as an unresolved polychotomy.
Tsuji and colleagues defined the group with the following features: distinct emargination at the posterolateral edge of the skull concave, smooth depression in the temporal region extending across most of the squamosal and large parts of the quadratojugal remaining area of the temporal region is characterized by distinctive dermal sculpturing a well developed, laterally protruding rim at its dorsal margin of the otic notch formed by the overhanging supratemporal and postorbital. All of these features have been equated with the presence of a tympanic membrane in the notch to facilitate hearing in this group.