Middle Cambrian molluscs of 'Australian' aspect from northern Siberia ALEXANDER P. GUBANOV, ARTEM V. KOUCHINSKY, JOHN S. PEELAND STEFAN BENGTSON GUnANOV, A.P., KOUCHINSKY, A.V., PnEL, J.S. &; BENGTSON, S., 30.4.2004. Middle Cambrian molluscs of 'Australian type' from northern Siberia. Alcheringa 28, 1-20. ISSN 0311- 5518. An assemblage of silicified helcionelloid molluscs is described from the Kuonamka Formation (Middle Cambrian Amgan Stage) of the Bol'shaya Kuonamka and Malaya Kuonamka rivers, northern Anabar Shield, northern Siberia. In addition to the new genera Kuonamkaella and Anabaroconus, the assemblage contains species of Yochelcionella, Eotebenna, Pseudomyona, and Protowenella. These latter genera were previously unknown from the Middle Cambrian of Siberia and indicate a strong affinity with coeval molluscan faunas from the Australian Middle Cambrian. The fauna provides evidence for close palaeogeographie links to East and West Gondwana, Baltica, and Laurentia during the Middle Cambrian, and facilitates biostratigraphiccorrelation between these crustal blocks. Alexander P. Gubanov [alexander.gubanov@pal.uu.se], Artem V. Kouchinsky [akouchin@maiLucla.edu], John S. Peel [john.peel@pal.uu.se], Department of Earth Sciences (Palaeontology), Uppsala University, Norbyviigen 22, SE-752 36 Uppsala, Sweden [present address of A. E Kouchinsky: Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095-1567, USA]; Stefan Bengtson [stefan.bengston@nrm.se], Department of Palaeozoology,Swedish Museum of Natural History, Box 50007, SE- I 04 05 Stockholm, Sweden; received l 4.11.2002, revised 17.4.2003. Key words: Mollusca, helcionelloids, Middle Cambrian, Siberia. VARIATION in our knowledge of Early and Middle Cambrian molluscs from different regions adversely affects the utility of molluscs for biostratigraphic and biogeographic purposes and impedes the discrimination of evolutionary lineages. Siberian helcionelloid molluscs from the Early Cambrian, especially from the Tommotian and Atdabanian, have been intensively studied (Vostokova 1962, Rozanov et al. 1969, Missarzhevsky 1989, Vassiljeva 1990, 1996), but the molluscs from overlying strata have received little attention. In contrast, molluscs from the late Early and Middle Cambrian in Australia, New Zealand and elsewhere exhibit an array of new morphologies (Runnegar & Jell 1976, MacKirmon 1985, Geyer 1986, Bengtson et al. 1990, Partdaaev 2001). However, the paucity of descriptions of the earlier Cambrian molluscs from these 0311/5518/2004/01001-20 $3.00 ©AAP localities makes it difficult to trace the ancestry of these faunas. A silicified Middle Cambrian molluscan fauna, described herein from the Kuonamka Formation of northern Siberia, contains helcionelloids such as Eotebenna Runnegar & Jell, 1976, Protowenella Runnegar & Jell, 1976, Pseudomyona Runnegar, 1983, and Yochelcion- ella Runnegar & Pojeta, 1974, all previously unknown from the Middle Cambrian of Siberia. The fauna provides evidence for closer palaeogeographic links to East (Australia and New Zealand) and West (Spain and Morocco) Gondwana, Baltica and Laurentia in the Middle Cambrian, and facilitates direct biostratigraphic correlation between these crustal blocks. Material and methods Material described herein was obtained in 1996 Downloaded By: [Univ of Cambridge] At: 13:11 3 June 2009