DZIK, J.: Anatomical information content in the Ediacarian fossils

Various modes of preservation of the Ediacarian fossils within different sediments, the sand at Zimnie Gory in northern Russia and lime mud at Khorbusuonka in northern Yakutia, show that the sediment was liquid long after formation of the imprints and that its mineralogy did not matter. The presence of a cyanobacterial mat stabilizing the sediment surface is necessary to explain formation of imprints of Yorgia on the clay bottom surface. The soft body impressions on the lower surface of the sand bed required a source of organic matter that promoted precipitation of pyrite cementing the sand bed base. However, the mat was of no importance in preservation of the Rangea bodies collapsed within the sand, or Pteridinium and Ventagyrus organic sheets loaded with sand within the suspended sediment. In many cases different parts of the same organism are preserved differently, either in a direct contact with the mat, or distant from it. If properly understood, those different modes of preservation may allow inference on various anatomical structures of the Ediacarian organisms. The Yorgia -style imprints offer evidence on the body surface morphology. Various stages of collapse of the bodies imprinted on the lower surface of the rock bed may provide insight into the internal anatomy of the organism. Its internal cavities may be filled with sediment, collapse under sediment load or, instead, resist collapse. The diversity of the Ediacarian anatomies restored in this way show the presence of organisms with radial, bilaterally symmetric, and asymmetric body plans. They have a lot in common, and the Ediacarian Vendobionta may be truly monophyletic, but their relationship to some Phanerozoic animal phyla is likely.