Anatomy of Emeroleter levis and the phylogeny of the nycteroleter parareptiles

ABSTRACT

The nycteroleter parareptiles have lately become the focus of increased attention, owing to their recently recognized sister-group relationship to pareiasaurs and the discovery an impedance-matching ear in members of the group. The Kotel’nich locality in central Russia dates to the early part of the Late Permian and preserves a diverse tetrapod fauna that includes the pareiasaur Deltavjatia vjatkensis and the nycteroleter Emeroleter levis. The latter taxon was previously known only from isolated crania, but recent excavations have produced additional material, including well-preserved postcrania, allowing a complete redescription. The skull of Emeroleter is typified by dermal sculpturing consisting of evenly spaced small, round pits and supratemporals that extend posterolaterally into broad horns. The quadratojugal is long and the posterior portion of the element curves dorsally into a pointed projection, an autapomorphy of the taxon. Postcranially, Emeroleter is very gracile with a long, sigmoid femur, and slender limbs, carpal, and tarsal elements. A reassessment of the Russian nycteroleters results in the synonymy of Tokosaurus perforatus with Macroleter poezicus. Phylogenetic analysis of parareptilian relationships using both parsimony and Bayesian inference yields a monophyly of ‘nycteroleters’ in parsimony, whereas the group is found to be paraphyletic with Bayesian inference. The genus Bashkyroleter is consistently paraphyletic. A clade consisting of the nycteroleters and pareiasaurs, here termed Pareiasauromorpha, is supported by both methods.

ACKNOWLEDGMENTS

The authors wish to thank A. Khlyupin (Kotel’nich Paleontological Museum, Kotel’nich), V. Bulanov, V. Golubev, and Y. Gubin (Paleontological Institute, Moscow), for access to collections and loan of specimens, H. Stöhr, who excellently prepared a number of the specimens studied in this project, and E. Maxwell, A. Huttenlocker, and C. Bickelmann for discussion. Laura Säilä, S. Sumida, and S. Modesto provided helpful reviews that greatly improved the manuscript. Funding for this project was provided by a grant of the Deutsche Forschungsgemeinschaft (DFG Mu 1760-/2-3) and a National Geographic grant to R.R.R. as well as a Discovery Grant from the Natural Sciences and Engineering Research Council (NSERC) of Canada to R.R.R.

Handling editor: Sean Modesto