Journal of Vertebrate Paleontology 25(2):402–413, June 2005 © 2005 by the Society of Vertebrate Paleontology LYSTROSAURUS GEORGI, A DICYNODONT FROM THE LOWER TRIASSIC OF RUSSIA MIKHAIL V. SURKOV1, NIKOLAS N. KALANDADZE2, and MICHAEL J. BENTON3 1Geology Institute of Saratov University, Astrakhanskaya 83 st., 410075 Saratov, Russia,
[email protected] 2 Paleontologicheskii Institut, Profsoyuznaya 123, 117647 Moscow, Russia. 3Department of Earth Sciences, University of Bristol, Bristol, BS8 1RJ, U.K.,
[email protected] ABSTRACT—The postcranial skeleton of Lystrosaurus georgi from the lowermost Triassic of the Moscow Basin, Russia, is described for the first time. This species retains contact between the premaxillae and palatine and is characterized by a narrow and elongated ischium, an autapomorphy for this species. Phylogenetic analysis of 27 Permian and Triassic dicynodont taxa using 18 postcranial characters confirms other recent hypotheses, but does not support a close relation- ship between Cistecephalus and Kingoria. The low homoplasy level among characters of the pelvis and femur, compared with the shoulder girdle and forelimbs, suggests that the former region documents the pattern of anomodont evolution better than the latter. Analysis of character changes revealed that a general evolutionary trend in the dicynodont postcranium relates to acquisition of semisprawling locomotion. INTRODUCTION Triassic; and from South America: Stahleckeria potens (UT n2), Santa Maria Formation , Middle Triassic; Kannemeyeria semi- Lystrosaurus was a famous survivor of the end-Permian mass cephalus (BMNH 3740). We also referred for comparison to extinction, and it became widespread in the Early Triassic, when descriptions of postcranial skeletons by Camp and Welles (1956), representatives of this genus were the dominant component in Cox (1959, 1965; 1972), Watson (1960), Ewer (1961), Cruicks- tetrapod assemblages worldwide.