Boreskov

PP‐10FUNGAL‐LIKE ELEMENTS IN THE CONSTRUCTION OF THE RIPHEANUNICELLULAR MICROFOSSILSGerman T.E., Podkovyrov V.N.Institute of Precambrian Geology and Geochronology RAS,Makarova emb., 2, St.‐Petersburg 199034, Russia, e‐mail: vpodk@mail.ruPrecambrian microfossils are useful in comparative studies of such fundamental aspectsas the transition from unicellular to multicellular organization. The specific population of theRiphean unicellular organisms has been described from ~1Gyr sediments (Lakhanda Group,Uchur‐Maya region, SE Siberia). They have been recorded in shales and consistentlyassociated with water‐deposited sediments. Unicells having a hollow shell of highly variedshape (spherical, ellipsoidal, elongate or sometimes polygonal) are composed of an organicsubstance and show net‐like distribution.A considerable number of Precambrian genera remained of undetermined affinity andgenera defined on morphology only, without implication as to relationships, it is undesirablethat they should be classed into the Linnaean hierarchy of orders and families. It is clearlypreferable that any classification, adopted should give no false impression of any naturalrelationship and should facilitate the easy transfer away of genera when their affinities cameto be determined. The lakhandinian microfossils were interpreted as probable yeasts thathave evidence in growth habit, general morphology, mode of reproduction commonly canbe discerned features that provide a basis for comparison of extant and fossil taxa. Ripheanunicells display the coincidence of their morphology, the mode of typical multilateralbudding of Saccharomyces and give additional evidence of the very early existence of suchbiological organization. These organic‐walled fossils have been described asEosaccharomyces ramosus Herm. (Hermann, 1979). Precambrian unicellular organismsextremely numerous and show innovations in biologic organization involved in theevolutionary transition from a single cell to multicellular pseudo tissue‐like microcolonies.Adjacent or loosely connected cells in these colonies tend to be similar texture andcolor, but differ in their diameter and shape. The connection between adjacent cells incolonies is usually with indication of cytoplasmic connection. Within an array fossils areequidimensional, but more often with one of the cells two to three times longer than itsneighbor and resemble sack‐like body called an ascus. There are some spheroidal structures148