Proceedings of the Zoological Institute RAS Vol. 319, No. 2, 2015, рр. 141–181 УДК 599.3 TAXONOMIC REVISION OF TRIBOSPHENIC MAMMALS FROM THE LOWER CRETACEOUS ANTLERS FORMATION OF TEXAS AND OKLAHOMA, USA A.O. Averianov 1, 2 1Zoological Institute of the Russian Academy of Sciences, Universitetskaya Emb. 1, 199034 Saint Petersburg, Russia; e-mail:
[email protected] 2Department of Sedimentary Geology, Geological Faculty, Saint Petersburg State University, 16 Liniya VO 29, 199178 Saint Petersburg, Russia ABSTRACT There are five taxa of tribosphenic mammals in the Early Cretaceous Antlers Formation of Texas and Oklahoma, USA: a basal stem therian (Kermackia texana), stem therians near the eutherian-metatherian dichotomy (Holoclemensia texana and Pappotherium pattersoni), and stem marsupials (Atokatheridium boreni and Oklatheridium szalayi). K. texana has a primitive therian postcanine formula with three molars, replacement of p5, M3 with low protocone and no conules, lower molars with a large trigonid angle, oblique protocristid, paraconid smaller than metaconid (except m3), strong distal metacristid, narrow talonid, small talonid basin, and small entoconid (absent on m3). H. texana also has replacement in the fifth premolar locus and three molars. It is more derived in having a larger proto- conal region with higher protocone and conules present, lack of distal metacristid, smaller trigonid angle, transverse protocristid, and wide talonid with larger talonid basin. It is similar to Eutheria by having M1 with reduced ecto- flexus, semimolariform p5, and low trigonid angle with transverse protocristid. Holoclemensia cannot be referred to Eutheria because of the lack of the second rank postvallum/prevallid shear and unwinged conules. P. pattersoni (=Slaughteria eruptens) has replacement in the fifth premolar position, premolariform p5, and three molars (symple- siomorphies for Theria).