Mammal remains from the Middle Jurassic (Bathonian) Berezovsk Quarry on the south of Krasnoyarsk Territory, West Siberia, Russia are referred to Docodonta indet. (two edentulous fragmentary dentaries) and Mammalia indet. (a single-rooted tooth). The dentaries exemplify a unique combination of plesiomorphic characters found among stem mammals only in Docodonta and Morganucodon: well developed Meckel's groove, trough for postdentary bones with overhanging medial ridge and a diagonal ridge on the floor separating the 'adductor fossa' and angular facet, and well developed and posteroventrally directed pseudangular process with facet for the reflected lamina of angular. Both specimens share with Docodonta the prearticular facet placed ventral to the angular facet and extending posteriorly to the mandibular foramen. This facet is not present in Morganucodon, where the prearticular lies medial to the angular. Medial position of the prearticular in Morganucodon is connected with the compound jaw articulation in this genus, in which a rudimentary articular-quadrate mandibular joint is present medially to the dentary-squamosal joint. In Docodonta indet. from Berezovsk Quarry, Haldanodon and Docodon the position of the prearticular ventral to the angular is connected with the position of the articular complex ventral to the dentary condyle. Such articular complex could not function as a mandibular joint and postdentary bones in Docodonta were used solely for sound transmission. One specimen from Berezovsk Quarry shares with Morganucodon a groove for replacement dental lamina, which was not reported previously for Docodonta. Mammal remains from Berezovsk Quarry are among the oldest occurrences for Docodonta, the first record of Jurassic mammals for Siberia, and only second such record for the whole of Russia.

Key words: Docodonta, Morganucodon, dentary, anatomy, Bathonian, Jurassic, Siberia.

Alexander O. Averianov [sasha@AA1923.spb.edu], Zoological Institute, Russian Academy of Sciences, Universitetskaya nab. 1, Saint Petersburg 199034, Russia; Alexey V. Lopatin [alopat@paleo.ru], Paleontological Institute, Russian Academy of Sciences, Profsouznaya ul. 123, Moscow 117997, Russia; Pavel P. Skutschas [skutchas@mail.ru], Department of Vertebrate Zoology, Biological Faculty, Saint Petersburg University, Universitetskaya nab. 7/9, Saint Petersburg 199034, Russia; Nikolai V. Martynovich [mnv@kkkm.ru], Krasnoyarsk Territory Regional Museum, ul. Dubrovinskogo 84, Krasnoyarsk 660049, Russia; Sergei V. Leshchinskiy [sl@ggf.tsu.ru] and Alexey V. Fayngertz [alex@ggf.tsu.ru], Department of Palaeontology and Historical Geology, Geological−Geographical Faculty, Tomsk State University, Prospekt Lenina 36, Tomsk 634050, Russia; Anton S. Rezvyi [Anton@isav.usr.pu.ru], Laboratory of Palaeontology, Institute of Earth Crust, Geological Faculty, Saint Petersburg University, 16 liniya VO 29, Saint Petersburg 199178, Russia; Sergei A. Krasnolutskii, Sharypovo Regional Museum, 6 microraion, Sharypovo 662311, Krasnoyarsk Territory, Russia.