Boreskov

PP‐58EARLY CAMBRIAN EVOLUTION OF SMALL SHELLY FOSSILSNovozhilova N.V.Institute of Petroleum Geology and Geophysics SB RAS, Prosp. Akad. Koptyuga 3,Novosibirsk, Russia, 630090, E‐mail: NovozhilovaNV@ipgg.nsc.ruThe appearance and evolution of animal organisms capable to a biomineralization onPrecambrian ‐ Cambrian boundary – the major stage in the biosphere development,characterized by "explosive" occurrence the most of types and classes of the animals existingtill now. The special place occupies small shelly fossils (SSF) – are a group of problematicorganisms containing chancelloriids, protoconodonts, molluscs, hyoliths, paleoscolecids,sponges and others, most are short‐lived and have no modern analogues. The complexes ofSSF assemblages Siberia, Mongolia, China and Australia are the most numerous and diverse.Question of the origin of mineralized skeletons is still debatable.The beginning of Lower Cambrian the Siberian platform as well as around the worldrelated to the onset of regressive cycle. Notes outbreak of speciation in most groups of SSF(Chancelloriids, Sachitids, Siphonoguchitids, Halkieriids, mollusks, et al.), but have appearedpreviously observed complication of morphological elements. Phosphatic structures arediscovered in the tube interior of the hyolithelminth species Hyolithellus vitricus from theLower Cambrian of the Siberian Platform. Anatomic interpretation of these structuressuggests that these small sized shelly fossils represent the earliest worm shaped organismsprobably closely related to modern Nemathelminthes (Novozhilova, 2010). Most workersconsidered these organisms as the order Hyolithelminthes Fisher, 1962 of uncertainsystematic position, or assigned it to the phylum Annelida. Hyolitelmintes find out rather lowrates of evolution, but the fact of their mass occurrence and blossoming in bottom ofCambrian on a global scale does this group by reliable enough marker of the Lower Cambrianboundary. At the beginning of Atdabanian stage starts declining species and quantification ofSSF biodiversity. By the end of stage their number is significantly reduced, in addition, to thismoment end their existence Angutiochreida, Sahitida, and most species of Tommotiida.Since this time the same peak in the development of Cambrian organogenic constructions inthe world. Complex skeletal problematic organisms is not representative in the Botomianstage, the majority of species ‐ the transit of the more ancient deposits.Thus the small shelly fauna, presented benthic organisms, predominated in the EarlyCambrian (Tommotian ‐ Atdabanian stages) ecosystems and gradually loses its value to theend (Botomian, Toyonian stages). Further studies require a more detailed examination andreconsideration of the systematics of all problematic organisms.[1]. Novozhilova N.V. New Data on the Morphology and Systematics of Hyolithelminthes (CambrianProblematic Organisms) // Paleontological Journal, 2010, Vol. 44, No. 2, pp. 120–124.235