Mikhail A. Fedonkin

The late Precambrian fossil Kimberella is a mollusc-like bilaterian organism

The fossil Kimberella quadrata was originally described from late Precambrian rocks of southern Australia. Reconstructed as a jellyfish, it was later assigned to the cubozoans (‘box jellies’), and has been cited as a clear instance of an extant animal lineage present before the Cambrian. Until recently, Kimberella was known only from Australia, with the exception of some questionable north Indian specimens. We now have over thirty-five specimens of this fossil from the Winter Coast of the White Sea in northern Russia. Our study of the new material does not support a cnidarian affinity. We reconstruct Kimberella as a bilaterally symmetrical, benthic animal with a non-mineralized, univalved shell, resembling a mollusc in many respects. This is important evidence for the existence of large triploblastic metazoans in the Precambrian and indicates that the origin of the higher groups of protostomes lies well back in the Precambrian.

The origin of the Metazoa in the light of the Proterozoic fossil record

Abstract Origin of the eukaryotic organisms (including the multicellular animals or Metazoa) is commonly considered to be related to growing oxygen content in the atmosphere up to a level that allows aerobic metabolism. Here it is suggested that oxygenation of the biosphere was not a permissive condition but rather a forcing factor that drove evolution towards the formation of complex biological systems. Growing concentration of free oxygen in conjunction with other geohistorical trends acted to chemically impoverish the ocean and atmosphere and made many of the chemical elements immobile or unavailable for metabolic processes. Of particular importance in this connection was the decreasing concentration in sea water of the heavy metals that demonstrate high catalytic ability and make an active center in many enzymes. Increasing biological complexity and the eukaryotization of the biosphere (origin of the eukaryotic cell, growing role of heterotrophy, increasing biodiversity, rise of multicellular organisms, lengthening of trophic chains, acceleration of biological recycling of the chemical elements, etc.) can be considered as an evolutionary response to the geochemical deterioration of the environment. Recent discoveries of the oldest megascopic eukaryotes, such as spiral Grypania (1.9 Ga), the necklace-like colonial organism of tissue-grade organization Horodyskia (1.5 Ga), vermiform Parmia (about 1.0 Ga) and Sinosabellidites (800 Ma ago) are consisitent with the “molecular clock” models on an early origin of animals; metazoans were, however, confined to relatively cold and well oxygenated basins beyond the carbonate belt of the ocean until the end of the Proterozoic. Large and diverse invertebrates of the Vendian Period are known mostly from siliciclastic marine basins. This fauna is characterized by high density of the benthic populations and well established clades both at the diploblastic (e.g., Phylum Trilobozoa) and triploblastic (e.g., Phylum Proarticulata) grades of organization as well as some taxa related to the Paleozoic phyla. An organic skeleton preceded the rise of the mineralized skeleton in some metazoan phyla. Low temperature of the habitats inhibited biomineralization. Almost simultaneous development of the phosphatic, carbonate and siliceous skeletons in different metazoan groups at the beginning of the Cambrian Period some 545 Ma ago could be related to the colonization of the warm carbonate basins by the metazoans. An additional factor for the rapid diversification of the biomineralized phyla could be the growing length of the trophic chains brought about by the rapidly increasing biodiversity and the need for detoxification at the top of the trophic pyramid. Being the byproduct of detoxification, sclerites and spicules, hard mineralized shells and carapaces immediately became an important factor of morphological evolution and growing biodiversity, as well as the object of intensive selection under the growing pressure of predators. Explosive growth of morphophysiological diversity in metazoans during the Vendian and Cambrian had an enormous impact on evolution of other groups of organisms and on the environment.

New data on Kimberella, the Vendian mollusc-like organism (White Sea region, Russia): palaeoecological and evolutionary implications

Abstract The taphonomic varieties of over 800 specimens of Kimberella (collected from the Vendian rocks of the White Sea region) provide new evidence of the animals anatomy such as: shell morphology, proboscis, mantle, possibly respiratory folds and possibly musculature, stomach and glands. Feeding tracks, crawling trails and, presumably, escape structures preserved along with the body imprint provide insights on the mode of locomotion and feeding of this animal. The shield-like dorsal shell reached up to 15 cm in length, 5–7 cm in width, and 3–4 cm in height. The shell was stiff but flexible. Evidence of dorso-ventral musculature and fine transverse ventral musculature suggests arrangement in a metameric pattern. Locomotion may have been by means of peristaltic waves, both within the sediment and over the surface of the sea floor, by means of a foot resembling that of monoplacophorans. Respiration may have been through a circumpedal folded strip (possibly an extension of the mantle). Feeding was accomplished by a retractable proboscis bearing terminal hook-like organs and provided with a pair of structures interpreted here as glands. Whilst feeding, Kimberella moved backwards. The structural complexity of Kimberella poses questions about the time of origin of the triploblastic metazoans.

Evolution and dispersal of deepsea traces

Metazoa evolved in shallow water seas in the late Precambrian, and there was a concomitant increase in abundance and diversity of trace fossils that reached very high levels by the Early Cambrian. There may have been some colonization of deep water, as evidenced by the «soft-bodied» fauna at Mistaken Point, Newfoundland but it was mostly by sessile animals which left few trace fossils. Shallow water late Precambrian and Early Cambrian sequences have yielded not only shallow water trace fossils but also many examples of traces typical of later deep water deposits. Significant colonization of the deep oceans by trace making animals was, however, delayed until the Early Ordovician

Reconstructing Rangea: New Discoveries from the Ediacaran of Southern Namibia

Abstract Rangea is the type genus of the Rangeomorpha, an extinct clade near the base of the evolutionary tree of large, complex organisms which prospered during the late Neoproterozoic. It represents an iconic Ediacaran taxon, but the relatively few specimens previously known significantly hindered an accurate reconstruction. Discovery of more than 100 specimens of Rangea in two gutter casts recovered from Farm Aar in southern Namibia significantly expands this data set, and the well preserved internal and external features on these specimens permit new interpretations of Rangea morphology and lifestyle. Internal structures of Rangea consist of a hexaradial axial bulb that passes into an axial stalk extending the length of the fossil. The axial bulb is typically filled with sediment, which becomes increasingly loosely packed and porous distally, with the end of the stalk typically preserved as an empty, cylindrical cone. This length of the axial structure forms the structural foundation for six vanes arranged radially around the axis, with each vane consisting of a bilaminar sheet composed of a repetitive pattern of elements exhibiting at least three orders of self-similar branching. Rangea was probably an epibenthic frond that rested upright on the sea bottom, and all known fossil specimens were transported prior to their final burial in storm deposits.

Causes and consequences of eukaryotization through mutualistic endosymbiosis and compartmentalization

This paper reviews and extends ideas of eukaryotization by endosymbiosis. These ideas are put within an historical context of processes that may have led up to eukaryotization and those that seem to have resulted from this process. Our starting point for considering the emergence and development of life as an organized system of chemical reactions should in the first place be in accordance with thermodynamic principles and hence should, as far as possible, be derived from these principles. One trend to be observed is the ever-increasing complexity resulting in several layers of compartmentalization of the reaction system, either spatial (of which the eukaryotic cell is an example), or functional (as in the gradually deepening distinction between metabolic, enzymatic and information-storing functions within the cell). One of the causes of this complexification of living systems will have been the changes in environmental conditions, particularly the geochemical impoverishment of the biosphere during geological history, partly brought about by living systems themselves, and partly by the trend towards increasing efficiency and specificity of the reactions that occur.

Metameric features in the Vendian metazoans

Abstract Metamerism as the serial homology is widespread among the Vendian (Late Precambrian) metazoans. Prevalence of segmented forms among the Vendian Bilateria suggests that in many phylogenetic lineages of Metazoa the evolutionary development of the bilateral symmetry and metamerism were related processes. Large number of coelenterate‐grade forms with serially homologous parts may indicate that at the earlier, pre‐Vendian stages of the metazoan history metamerism could be at great extent realised at the diploblastic level.

Ventogyrus, a possible siphonophore-like trilobozoan coelenterate from the Vendian Sequence (late Neoproterozoic), northern Russia

Abstract Complex internal anatomy is documented for the first time in a Neoproterozoic soft-bodied invertebrate. New data suggests that Ventogyrus, originally described as a sessile, boat-shaped form belonging to the enigmatic Neoproterozoic group Petalonamae, is actually composed of three, identical modules, arranged around an axial rod. Each module has one longitudinal and numerous transverse septa, which delimit chambers of decreasing size from one end to the other. Three distinct longitudinal channels with alternating lateral branches make up an internal network, perhaps a circulatory system. Ventogyrus is a most unusual form, particularly in the quality of its three dimensional preservation of a complex internal structure and a three-fold symmetry, a symmetry shared by many Ediacarans.

Geobiological Trends and Events in the Precambrian Biosphere

Reconstruction of the global biological events in the Precambrian requires a multidisciplinary approach. Data from the poor fossil record of the prokaryotes has to be supplemented by the interpretation of some sedimentological, geochemical and paleoclimatic phenomena as the biologically controlled processes. Biochemical and ecological conservatism of the prokaryotic ecosystems makes it possible to decode their signals documented in the Precambrian geological history. Expansion of the eukaryotes was the cause of the strong transformation of the fossil record as a whole. In addition to the biological innovation represented by the growth and change in the taxonomic diversity and cell (or body) size of the organisms, there were other global bio-events connected with the restructuring of the ecosystems, colonization of new environments, and rise of new physiologies which strongly affected the sedimentological and taphonomic processes.

PaleoParks - The Protection and Conservation of Fossil Sites World-Wide

The world-famous Vendian (Ediacaran) fossil biota in the White Sea - Arkhangelsk region of Russia contains some of the most exquisite fossils of the earliest macrobiota (560-545 million years old) on Earth. Over 600m of continuously fossiliferous strata consisting of fine sand, silt and mud crop out at many localities along the White Sea. The fossils have been under study for decades in Moscow and that work continues. These fossils represent unusual taxa of early metazoans, algae, microbial mats, and strange sedimentary impressions that represent a very early stage of development of animals on Earth. These unique fossils have been well publicized through exhibitions, newspaper articles, scientific research papers and various web sites. As a result and in spite of their remote location, they are endangered by unauthorized fossil collectors. These paleo-pirates violate local and national laws, destroy fossils and fossil sites, and leave debris and garbage in the area. Some scientific papers are, surprisingly, based on illegally-collected fossils. Other illegal fossils have been offered for sale by commercial fossil dealers, chiefly at meetings or through web purchases. Paleo-piracy of the Vendian biota must be stopped. The collection of fossils has been illegal since February 2000 by the authority of the Administration of the Arkhangelsk Region and the Northern Committee of Natural Resources of the Russian Ministry of Natural Resources. Presently, the Ministry of Internal Affairs and Federal Security Service are prepared to protect the Vendian localities by arresting pirates. Recommendations to control paleo-piracy in the White Sea region include finalizing the establishment of World Heritage Site status, educating the local people in the values of the fossils and the need for their protection, establishment of a procedure for licensing for the collection of some fossils, and the notification to sellers of Vendian material by Russian authorities that the fossils were obtained illegally and hence are the property of Russia.