Onega stepanovi is one of the lesser known fossil taxa

Ediacara biota

The Ediacara biota consisted of enigmatic tubular and frond-shaped, mostly sessile organisms which lived during the Ediacaran Period . Trace fossils of these organisms have been found worldwide, and represent the earliest known complex multicellular organisms.Simple multicellular organisms such as...

 from the Ediacaran

Ediacaran

The Ediacaran Period , named after the Ediacara Hills of South Australia, is the last geological period of the Neoproterozoic Era and of the Proterozoic Eon, immediately preceding the Cambrian Period, the first period of the Paleozoic Era and of the Phanerozoic Eon...

 Period. It was described by Mikhail A. Fedonkin

Mikhail A. Fedonkin

Dr. Mikhail Aleksandrovich Fedonkin is an awarding winning paleontologist specializing in documentation of the earliest animals' body fossils, tracks, and trails. He was the first to describe several fossils including Hiemalora, Onega stepanovi, and Nimbia occlusa.Fedonkin is fluent in English and...

 in 1976
and was placed in the Phylum

Phylum

In biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....

 Proarticulata

Proarticulata

Proarticulata is a proposed extinct phylum of very early bilateral animals known from fossils found in the Ediacaran fauna. Mikhail A. Fedonkin describes animals in Proarticulata as having a "shield-like" shape, an unmineralized, thin, flexible carapace and a thick, segmented body...

 in 1985.
It was named after the Onega Peninsula

Onega Peninsula

The Onega Peninsula is located in Arkhangelsk Oblast, Russia. It protrudes into the White Sea, with Onega Bay to the south-west, and Dvina Bay to the north-east. The length of the peninsula is about , and the width varies between and .-Geography:...

 in Russia's White Sea

White Sea

The White Sea is a southern inlet of the Barents Sea located on the northwest coast of Russia. It is surrounded by Karelia to the west, the Kola Peninsula to the north, and the Kanin Peninsula to the northeast. The whole of the White Sea is under Russian sovereignty and considered to be part of...

, where the first specimens of Onega stepanovi were found in outcrops on the Syuz’ma River. Its species name honors V. A. Stepanov, discoverer of the first Ediacaran fossil locality in Arkhangelsk Region, on the Lentniy Bereg (Summer Coast) of the Onega Peninsula in 1972.

Morphology

The small fossils, which range up to 7 millimetre (0.275590551181102 in) long, have oval outlines and low bodies with an articulated central zone built of isomers

Isomer (Proarticulata)

Isomer is an element of transverse body articulation of the bilateral fossil animals of the Phylum Proarticulata from the Ediacaran period. This term has been proposed by Andrey Yu...

 encircled by an undivided zone. The surface of the undivided region of Onega is covered with small tubercles.

Onega was originally described by Mikhail Fedonkin as a problematic organism, being grouped together with Vendia

Vendia

Vendia is an oval-shaped, Ediacaran fossil from 4.5 to 12.5 mm long. Its body is completely segmented into isomers, which are arranged alternately in two rows longitudinal to the axis of the body. The larger isomers cover the smaller ones externally but the posterior ends of all the isomers...

, Praecambridium and Vendomia as possible stem-group arthropod

Arthropod

An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

s due to a vague similarity with primitive Cambrian

Cambrian

The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...

 trilobite

Trilobite

Trilobites are a well-known fossil group of extinct marine arthropods that form the class Trilobita. The first appearance of trilobites in the fossil record defines the base of the Atdabanian stage of the Early Cambrian period , and they flourished throughout the lower Paleozoic era before...

s and arthropods.

In 1985 Mikhail Fedonkin erected Phylum

Phylum

In biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....

 Proarticulata, in which he placed: Onega, Dickinsonia

Dickinsonia

Dickinsonia is an iconic fossil of the Ediacaran biota. It resembles a bilaterally symmetrical ribbed oval. Its affinities are presently unknown; most interpretations consider it to be an animal, although others suggest it may be fungal, or a member of an "extinct kingdom".-Species variety:A...

, Palaeoplatoda, Vendia

Vendia

Vendia is an oval-shaped, Ediacaran fossil from 4.5 to 12.5 mm long. Its body is completely segmented into isomers, which are arranged alternately in two rows longitudinal to the axis of the body. The larger isomers cover the smaller ones externally but the posterior ends of all the isomers...

, Vendomia, Praecambridium and Pseudovendia sp., although he did not exclude the possibility that Onega may still be related to various lower Cambrian arthropods, such as Skania

Skania

Skania is a Cambrian fossil arthropod that may be related to the Ediacaran organism Parvancorina, and bears a strong, albeit superficial resemblance to the Vendiamorphans Vendia, Praecambridium and Onega...

.

Andrey Yu. Ivantsov has proposed that Onega be placed in phylum

Phylum

In biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....

 Proarticulata

Proarticulata

Proarticulata is a proposed extinct phylum of very early bilateral animals known from fossils found in the Ediacaran fauna. Mikhail A. Fedonkin describes animals in Proarticulata as having a "shield-like" shape, an unmineralized, thin, flexible carapace and a thick, segmented body...

, as the segments in recently discovered, exceptionally well-preserved fossils display the glide, or "staggered", symmetry characteristic of the majority of proarticulatans.

Research in progress by A. Yu. Ivantsov denies the presence of the "rigid dorsal carpace" М. Fedonkin observes in Onega and other protarticulatans..

Fossil record

Imprints of Onega stepanovi have been found in the Verkhovka and Zimnie Gory Formations
of the Ediacaran (Vendian) rocks of the Arkhangelsk Region, Russia.

All the fossil specimens are negative imprints on the bases of fine-grained sandstone beds with the "elephant skin" and tubercle texture diagnostic of microbial mat

Microbial mat

A microbial mat is a multi-layered sheet of micro-organisms, mainly bacteria and archaea. Microbial mats grow at interfaces between different types of material, mostly on submerged or moist surfaces but a few survive in deserts. They colonize environments ranging in temperature from –40°C to +120°C...

s.
The same bedding planes contain various other Ediacaran species: Cyclomedusa

Cyclomedusa

Cyclomedusa is a circular fossil of the Ediacaran biota; it has a circular bump in the middle and as many as five circular growth ridges around it. Many specimens are small, but specimens in excess of 20cm are known. The concentric disks are not necessarily circular, especially when adjacent...

, Ediacaria

Ediacaria

Ediacaria is a fossil genus dating to the Ediacaran Period of the Neoproterozoic Era. Unlike most Ediacaran biota which disappeared almost entirely from the fossil record at the end of the Period, Ediacaria fossils have been found dating from the Baikalian age of the Upper Riphean to 501 million...

, palaeopascichnids

Palaeopascichnus

Palaeopascichnus is a genus of Ediacaran organism comprising a series of lobes; it is plausibly a protozoan, but probably unrelated to the classical 'Ediacaran biota'....

, Eoporpita, Yorgia

Yorgia

Yorgia waggoneri is a member of the Ediacara biota, and resembles a cross between the organisms Dickinsonia and Spriggina. It has a low, segmented body consisting of a short wide "head", no appendages, and a long body region, reaching a maximum length of...

, Andiva, Archaeaspinus, Vendia

Vendia

Vendia is an oval-shaped, Ediacaran fossil from 4.5 to 12.5 mm long. Its body is completely segmented into isomers, which are arranged alternately in two rows longitudinal to the axis of the body. The larger isomers cover the smaller ones externally but the posterior ends of all the isomers...

, Dickinsonia

Dickinsonia

Dickinsonia is an iconic fossil of the Ediacaran biota. It resembles a bilaterally symmetrical ribbed oval. Its affinities are presently unknown; most interpretations consider it to be an animal, although others suggest it may be fungal, or a member of an "extinct kingdom".-Species variety:A...

, Anfesta, Albumares, Tribrachidium

Tribrachidium

Tribrachidium heraldicum was an early Ediacaran organism famous for its unusual tri-radial symmetry. It was named and first described from South Australia by Martin Glaessner and Brian Daily in 1959....

, Kimberella

Kimberella

Kimberella is a monospecific genus of bilaterian known only from rocks of the Ediacaran period. The slug-like organism fed by scratching the microbial surface on which it dwelt in a manner similar to the molluscs, although its affinity with this group is contentious.Specimens were first found in...

, Parvancorina

Parvancorina

Parvancorina is a genus of shield-shaped Ediacaran fossils. It has a raised ridge down the central axis of symmetry. This ridge can be high in unflattened fossils. At the 'head' end of the ridge there are two quarter circle shaped raised arcs attached. In front of this are two nested...

, Charniodiscus

Charniodiscus

Charniodiscus is an Ediacaran fossil that was probably a stationary filter feeder that lived anchored to a sandy sea bed. The organism had a holdfast, stalk and frond. The holdfast was bulbous shaped, and the stalk was flexible. The frond was segmented and had a pointed tip...

and others.