A. Yu. Ivantsov

New reconstruction of Kimberella, problematic Vendian metazoan

Six groups of fossil remains of Kimberella quadrata are described. They represent the imprints of the body in different types of preservation (including the group of specimens that are elongated more than twice in comparison with the common ones) and also the feeding traces and mucus secretions. The imprint is considered to be created only by the upper side of the body. The fossil material shows that Kimberella had hard sclerites, probably of aragonite, and several teeth in its mouth. Kimberella is suggested to have “the mantle” with sclerites, wider foot, which was spread over the outer surface of the mantle, and the strong transverse and longitudinal musculature.

Feeding traces of proarticulata—the Vendian metazoa

Three types of low-topography impressions are described from the Late Vendian, which are interpreted as the feeding traces of representatives of the phylum Proarticulata Fedonkin, 1985, which became extinct in the Precambrian. The producers of two types of trace were found. Impressions are usually large and arranged in groups; therefore their correct interpretation only became possible following large-scale excavation work that was carried out for the first time in the Late Vendian deposits of the Arkhangelsk Region in 1996–2001. The single trace (or trace platform) represents a copy of the whole ventral side of the body made by sandstone or only the part of it. Usually trace platforms are arranged in chains and orientated in one distinct direction. In spite of some superficial similarity, the fossils are neither body remains nor traces of post-mortem compression. The hypothesis of trace formation proposed suggests that the feeding strategy of Proarticulata was different from any feeding behavior known in large Phanerozoic animals. All types of imprints are identified as belonging to the genus Epibaion Ivantsov, 2002. It is proposed that the Australian fossil Phyllozoon Jenkins et Gehling, 1978 is also a feeding trace of Proarticulata.

Trace fossils of precambrian metazoans “Vendobionta” and “Mollusks”

Metazoan trace fossils from the Upper Vendian are preserved together with remains of corresponding organisms. The traces belong to “Vendobionta”, representing the Precambrian phylum Proarticulata and to a presumably trochophoran animal Kimberella quadrata. These organisms fed on microbial mats, which preserved fossil traces. Impressions of the mat surface structures, traces, and bodies of animals are preserved in marine terrigenous sediments on the basal surfaces of sandstone beds. Proarticulata grazing traces are represented by groups and chains of impressions left by the ventral side of a body or its central and posterior parts. Kimberella traces are represented by long ridges united into bundles, fans, and chains of fans. All these traces were largely formed mechanically, i.e., by mat scratching with cilia (Proarticulata) or teeth (Kimberella). Proarticulata representatives destroyed only a thin upper layer of the mat, while Kimberella could possibly scratch the mat through its entire thickness or even tear off pieces from it.

Paleontological evidence for the supposed precambrian occurrence of mollusks

AbstarctThe paper discusses a group of the Late Vendian fossils supposedly related to mollusks. The fossils include imprints with some anatomical characteristics of mollusks, traces resembling scratch marks left by radula, and structures resembling soft shells. Kimberella quadrata, which is represented by all the above kinds of fossils was most likely a trochophore animal of a pre-molluscan evolutionary stage. Remains of Armillifera parva and Solza margarita only slightly resemble shells, and in the absence of the knowledge on the soft body of these animals there are no enongh evidences affiliate them with mollusks.

Revision of the problematic Vendian macrofossil Beltanelliformis (=Beltanelloides, Nemiana)

Two groups of Precambrian macrofossils are reexamined. Members of the first group are usually determined as Nemiana simplex Palij, 1976 and regarded as remains of animal organisms; members of the second are often determined as Beltanelloides sorichevae Sokolov, 1965 and assigned to green algae or cyanobacteria. The co-occurrence of the two groups in burials of the White Sea outcrops, the similarity in morphology, and the presence of transitional forms suggest that they could have been variants of preservation of the same extinct species. As a result of critical analysis of published data and examination of available type specimens, the species Beltanelliformis brunsae Menner, 1974, Beltanelloides podolicus A. Istchenko, 1988, Hagenetta aarensis Hahn et Pflug, 1988, Medusinites paliji Gureev, 1987, and Namamedusium wendti Zessin, 2008 are assigned to the same species. Beltanelliformis brunsae is regarded as the senior synonym. Taphonomic and comparative morphological data and the SEM study of phosphatized remains of Beltanelliformis agree with the hypothesis developed by M. Steiner of the microbial nature of these fossils. It is proposed that round colonies of B. brunsae grew in the area of extremely shallow water in Late Vendian marine basins. Beltanelliformis minutae McIlroy et al., 2005 is the second species of the same genus; it was more tolerant of changes in salinity and shows a wider stratigraphic range, while the species Nemiana bakeevi Becker, 1992 and Beltanelloides amorphus Menasova, 2003 are considered to have nothing in common with the groups and genus discussed.

Reconstruction of Charniodiscus yorgensis (Macrobiota from the Vendian of the White Sea)

Reconstruction and new description of the rare species Charniodiscus yorgensis Borchvardt et Nessov, 1999, which has previously been represented by a single, presently lost specimen, is provided. New material collected in the type locality and closely situated outcrops of Zimnii Bereg of the White Sea allows reconstruction of the structure of this fossil form in more detail. Like other species of the genus Charniodiscus Ford, 1958, the specimen of C. yorgensis, replaced by pyrite initially nonmineralized skeleton of an organism, consisted of a bilobate frond with the rachis passing downwards into the basal disk. It is shown that each lobe of the frond of C. yorgensis was an entire membrane arranged in transverse folds, as an accordion. Plicate lateral lobes, with their free margins directed upwards, adjoin sharp ridges of folds on either side of the membrane. Semipouches formed of bends of lateral lobes were probably the bases of tubular or seedlike elements of branches of the second order, recognized in C. oppositus Jenkins et Gehling, 1978 and C. arboreus (Glaessner, 1959) from Australian localities. Unique records of C. yorgensis buried in an upstanding position corroborate the well-known hypothesis of the vertical lifetime orientation of Charniodiscus.

Small Vendian transversely Articulated fossils

Three new genera of transversely articulated Metazoa are described from the Upper Vendian of the Arkhangelsk Region (Russia). Tamga gen. nov. and Lossinia gen. nov. are recognized to be closely related to the extinct Precambrian phylum Proarticulata; Ivovicia gen. nov. is considered as a true member of Proarticulata; all of the new genera are monotypic. Onega stepanovi Fedonkin is also reinterpreted as Proarticulata. The replacement generic name Archaeaspinus is introduced for the preoccupied Archaeaspis Ivantsov. Vendomia menneri Keller is assigned to Dickinsonia Sprigg.

Growth variability in the late Vendian problematics Parvancorina Glaessner

Morphological and quantitative characteristics of the growth variability of two Parvancorina species were analyzed based on new abundant material from the Vendian of the White Sea. Growth variability in this problematic taxon appears to be wider than previously suggested. We found allometric growth in the White Sea population of P. minchami Glaessner, 1958, in contrast to isometric growth in Australian representatives of the species. Another White Sea species, P. sagitta Ivantsov, 2004, shows gradual formation of anchor-shaped structure in juveniles. Based on Australian material, it was previously believed that this structure did not change during ontogeny. These two distinctive features together with a strong variability of age-related measurements distinguish Parvancorina from other early arthropods (Scania, Primicaris), and cast doubt on the growth pattern as an argument in favor of the arthropodan nature of Parvancorina.

New data on Late Vendian problematic fossils from the genus Harlaniella

The morphology and stratigraphic distribution of Harlaniella podolica Sokolov, 1972 and H. ingriana Ivantsov, sp. nov. were investigated using the collection of impressions sampled recently in Upper Vendian sections of Russia (southeastern White Sea region) and Ukraine (Podoliya). These fossils, which were previously considered as representing coprolites or grazing or locomotion traces, are interpreted as internal casts and impressions of fragments of tubes of initially organic composition. Streptichnus narbonnei Jensen et Runnegar, 2005 from Vendian-Cambrian boundary strata of Namibia are also attributed to this group. It is assumed that the tubes are similar to remains of the algal genera Vendotaenia Gnilovskaya, 1971 from Vendian deposits of the East European Platform and Liulingjitaenia Chen et Xiao, 1992 from Sinian sections of China.

Kuckaraukia multituberculata: A new Vendian fossil from the basa formation of the Asha Group in the South Urals

A new macrofossil genus and species from the Late Vendian of the Urals is described. Fossils are found on a bedding plane between the sandstone and mudstone and are represented mainly by casts on the sandstone surface. The casts are negative and flat-bottomed, covered with numerous, closely spaced uniform indentations and rimmed by a small, low, narrow, flat flange. This fossil can be reconstructed as a disk consisting of two layers. The top layer was less resistant and probably unstructured. The bottom layer was denser and was structured (either with a tuberculate surface or consisted of loosely packed spherical elements). Kuckaraukia multituberculata gen. et sp. nov. could be interpreted as a unitary organism or as a colony of motionless benthic organisms.