BIOLOGY 622 – FALL 2014 BASAL AMNIOTA - STRUCTURE AND PHYLOGENY
WEEK – 10 PAREIASAUROMORPHA
S. S. SUMIDA
INTRODUCTION
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 1
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.
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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.
And, this is interesting because in 2007 Muller and Tsuji did provide a hypothesis of relationships for the nycteroleter parareptiles in their paper on hearing.
You will notice from this phylogeny that the “genus” Bashkyroleter” shows up in two different spots, so the two different species can’t be part of the same genus. They are in fact unique enough to be their own taxa, so they await further study to sort them out.
Additionally, Tokosaurus has been synonymized with Macroleter.
This leaves us with six genera currently considered valid:
REPTILIA; PARAREPTILIA; PAREIASAUROMORPHA; NYCEROLETERIDAE:
TAXON AGE / HORIZON LOCALITY Mezen River Basin, Arkhangel’sk Macroleter Middle Permian Province, Russia.
Rhipaeosaurus Middle Permian Beleby, Russia
Emeroleter Late Permian Town of Kotel’nich, Kirov Province, Russia.
Mezen River Basin, Arkhangel’sk Nycteroleter Middle Permian Province, Russia.
“Bashkyroleter” bashkyricus Middle Permian Beleby, Russia
Mezen River Basin, Arkhangel’sk “Bashkyroleter” mesensis Middle Permian Province, Russia. 3
SURVEY OF NYCTEROLETER PARAREPTILES
Macroleter and Emeroleter are the best known of the group. Notably, Emeroleter is the youngest of the group.
Macroleter Middle Permian Mezen River Basin, Arkhangel’sk Province, Russia and Oklahoma
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Notes: Macroleter has been suggested by Laurin and Reisz (2001) to also be in Oklahoma based on the specimen following:
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Rhipaeosaurus Middle Permian Beleby, Russia
Notes: Very little is known of this taxon, and there is particularly little cranial material except for some tricuspid teeth.
Nycteroleter Middle Permian Mezen River Basin, Arkhangel’sk Province, Russia.
Notes: This is the first member of the group to have been named, thus the family name. Unfortunately the type specimen has been lost. Referred specimens suggest it was amongst the smaller of nycteroleters
“Bashkyroleter” bashkyricus Middle Permian Beleby, Russia
Notes: A slightly more angular boxy skull compared to Nycteroleter
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“Bashkyroleter” mesensis Middle Permian Mezen River Basin, Arkhangel’sk Province, Russia.
Notes: A larger skull, and deeply incised otic notch. In dorsal the view the skull is nearly the dimensions of an isosceles triangle.
Emeroleter Late Permian Town of Kotel’nich, Kirov Province, Russia.
Due to the work of Tsuji, Emeroleter is one of the best prepared and best known of the Russian nycteroleters.
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DISTRIBUTION OF NYCTEROLETER PARAREPTILES
All of the nycteroleters are from the middle or late Permian of Russia:
In a present day map:
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And in a map of the Late Permian, with Pangea still united:
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