ISSN 0031-0301, Paleontological Journal, 2010, Vol. 44, No. 5, pp. 573–583. © Pleiades Publishing, Ltd., 2010 Original Russian Text © A.V. Lopatin, A.O. Averianov, E.N. Maschenko, S.V. Leshchinskiy, 2010, published in Paleontologicheskii Zhurnal, 2010, No. 5, pp. 90–98. 573 INTRODUCTION The present study continues a series of publications devoted to Early Cretaceous mammals of Western Sibe- ria, which was started with the description of the tin- odontid symmetrodont Yermakia domitor Lopatin et al., 2005 and the tegotheriid docodont Sibirotherium rossicum Maschenko et al., 2003 from the Shestakovo 1 locality (Lopatin et al., 2005, 2009). Below, we describe remains of Kiyatherium cardiodens Maschenko et al., 2002 from the Shestakovo 3 locality, which was referred in the original description to the eupantothere family Peramuridae (Maschenko et al., 2002). New material, including an upper jaw fragment and three lower jaw fragments with partially preserved teeth, suggests that this taxon belongs to the symmetrodont family Zhang- heotheriidae. The Shestakovo 3 locality is considered to be contemporaneous with the Shestakovo 1 locality; however, it has not yielded mammal species in common with the latter. The material described is housed the Paleontological Museum of Tomsk State University. The tomographic study of specimens was performed using a Skyscan 1172 x-ray microtomograph in the Borissiak Paleontological Institute of the Russian Acad- emy of Sciences. In the present study, we use the following abbrevia- tions: (PIN) Borissiak Paleontological Institute of the Russian Academy of Sciences, Moscow; (PM TGU) Paleontological Museum of Tomsk State University, Tomsk; (L) greatest length of the tooth crown; (W) greatest width of the tooth crown; (H) labial height of the tooth crown at the main cusp; (h) depth of the horizontal ramus of the lower jaw on the labial side under М 4 . Designations of tooth cusps are shown in Fig. 1. They are homologous to the following cusps of tribosphenic teeth (see Rougier et al., 2003b): cusp Early Cretaceous Mammals of Western Siberia: 3. Zhangheotheriidae A. V. Lopatin a , A. O. Averianov b , E. N. Maschenko a , and S. V. Leshchinskiy c a Borissiak Paleontological Institute, Russian Academy of Sciences, Profsoyuznaya ul. 123, Moscow, 117997 Russia e-mail: alopat@paleo.ru b Zoological Institute, Russian Academy of Sciences, Universitetskaya nab. 1, St. Petersburg, 199034 Russia e-mail: lepus@zin.ru c Tomsk State University, pr. Lenina 36, Tomsk, 634050 Russia Received November 26, 2009 Abstract—New material of Kiyatherium cardiodens Maschenko, Lopatin et Voronkevich, 2002 from the Early Cretaceous Shestakovo 3 locality (Kemerovo Region, Western Siberia) suggest that this taxon belongs to symmetrodont mammals of the family Zhangheotheriidae. Kiyatherium has relatively long and narrow upper and lower molars, with large trigon and trigonid angles (triangularity is approximately as pronounced as in Tinodontidae); a wide and deep Meckel’s groove; a reduced and strongly posteriorly inclined coronoid process of the lower jaw; a very deep posterior mandibular incisure; a strong pterygoid crest; and a small ptery- goid fossa. The evolutionary level of dental and mandibular morphology suggests that Kiatherium occupies a basal position in the family. The holotype of K. cardiodens shows replacement of the first molar, which is a unique case among Trechnotheria. Key words: Symmetrodonta, Zhangheotheriidae, Lower Cretaceous, Western Siberia. DOI: 10.1134/S0031030110050138 a A C D B E b e c d Sty (а) (b) Fig. 1. Designations of tooth cusps of Kiyatherium car- diodens Maschenko, Lopatin et Voronkevich, 2002: (a) left upper molar and (b) left lower molar. (Sty) stylocone.