''Cephalonega stepanovi'' is a fossil organism from Ediacaran deposits of the

Arkhangelsk Region Arkhangelsk Oblast (russian: Арха́нгельская о́бласть, ''Arkhangelskaya oblast'') is a federal subject of Russia (an oblast). It includes the Arctic archipelagos of Franz Josef Land and Novaya Zemlya, as well as the Solovet ...

, Russia. It was described by

Mikhail A. Fedonkin Academician Mikhail Aleksandrovich Fedonkin (russian: Михаи́л Алекса́ндрович Федо́нкин; born June 19, 1946) is a Russian paleontologist specializing in documentation of the earliest animals' body fossils, tracks, a ...

in 1976

Name

Its original genus name ''Onega'' comes from the Onega Peninsula of the

White Sea The White Sea (russian: Белое море, ''Béloye móre''; Karelian and fi, Vienanmeri, lit. Dvina Sea; yrk, Сэрако ямʼ, ''Serako yam'') is a southern inlet of the Barents Sea located on the northwest coast of Russia. It is s ...

, where the first fossils were found. The species name was given to honour V.A. Stepanov, who discovered the

Ediacaran The Ediacaran Period ( ) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and t ...

fossil site on the Letniy Bereg ("

Summer Coast The Summer Coast (''Letniy Bereg'', russian: Летний Берег) is a coastal area in Arkhangelsk Oblast in northwest Russia. It is located on the western side of the Dvina Bay in the White Sea, on the Onega Peninsula, between the Northern ...

") in 1972, on the Onega Peninsula, the first

Proterozoic The Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". It is also the longest eon of the Earth's geologic time scale, and it is subdivided ...

site found in the Arkhangelsk Oblast. The original generic name is previously occupied by the hemipteran genus ''Onega'' Distant (1908). Ivantsov ''et al.'' (2019) coined a replacement generic name ''Cephalonega''.

Morphology

The small fossils, which range up to long, have oval outlines and low bodies with an articulated central zone built of

isomers In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. ...

encircled by an undivided zone. The surface of the undivided region of ''Cephalonega'' is covered with small tubercles. ''Cephalonega'' was originally described by Mikhail Fedonkin as a problematic organism, being grouped together with ''

Vendia ''Vendia'' is a genus of oval-shaped, Ediacaran fossils ranging from 4.5 to 12.5 mm long. The body is completely segmented into isomers, which are arranged alternately in two rows longitudinal to the axis of the body. The larger isomers co ...

'', '' Praecambridium'' and ''

Vendomia ''Dickinsonia'' is an extinct genus of basal animal that lived during the late Ediacaran period in what is now Australia, China, Russia and Ukraine. The individual ''Dickinsonia'' typically resembles a bilaterally symmetrical ribbed oval. Its a ...

'' as possible stem-group

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...

s due to a vague similarity with primitive

Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ag ...

trilobite Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the ...

s and arthropods. In 1985 Mikhail Fedonkin erected

Phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclatu ...

Proarticulata,M. A. Fedonkin (1985). "Systematic Description of Vendian Metazoa". ''Vendian System: Historical–Geological and Paleontological Foundation, Vol. 1: Paleontology''. Moscow: Nauka, pp. 70–106. in which he placed: ''Cephalonega'', ''

Dickinsonia ''Dickinsonia'' is an extinct genus of basal animal that lived during the late Ediacaran period in what is now Australia, China, Russia and Ukraine. The individual ''Dickinsonia'' typically resembles a bilaterally symmetrical ribbed oval. Its a ...

'', ''

Palaeoplatoda ''Palaeoplatoda'' is a genus from the Ediacaran biota. It is a soft-bodied organism with a segmented body that resembles ''Dickinsonia'', another Ediacaran organism. Description ''Palaeoplatoda'' has a leaf-like, segmented body, that is simila ...

'', ''

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

Skania ''Skania'' is a Middle Cambrian fossil arthropod that is closely related to the Early Cambrian ''Primicaris'' from the Chengjiang Biota, China. It bears a superficial resemblance to the Ediacaran The Ediacaran Period ( ) is a geological ...

''.Stefan Hengtson; Mikhail A. Fedonkin; Jere H. Lipps. (1992). "The Major Biotas of Proterozoic to Early Cambrian Multicellular Organisms". In: Edited by J. William Schopf; Cornelis Klein. ''Proterozoic Biosphere''. Cambridge University Press, pp. 433–435. Andrey Yu. Ivantsov has proposed that ''Cephalonega'' should be placed in the

phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclatu ...

Proarticulata Proarticulata is a proposed phylum of extinct, bilaterally symmetrical animals known from fossils found in the Ediacaran (Vendian) marine deposits, and dates to approximately . The name comes from the Greek () = "before" and Articulata, i.e. pr ...

, as the segments in recently discovered, exceptionally well-preserved fossils display the glide, or "staggered", symmetry characteristic of the majority of proarticulatans. According to a recent study, all ''Cephalonega'' researchers agree that it is proarticulatan and put it in the class Cephalozoa that also includes e.g. ''

Yorgia ''Yorgia waggoneri'' is a discoid Ediacaran organism. It has a low, segmented body consisting of a short wide "head", no appendages, and a long body region, reaching a maximum length of . It is classified within the extinct animal phylum Proarti ...

'', ''

Andiva ''Andiva ivantsovi'' is a Vendian fossil, identified to be a bilaterian triploblastic animal in the Ediacaran phylum Proarticulata, known from the Winter Coast, White Sea, Russia. It was first discovered in 1977, and described as a new species ...

'' and ''

Spriggina ''Spriggina'' is a genus of early bilaterian animals whose relationship to living animals is unclear. Fossils of ''Spriggina'' are known from the late Ediacaran period in what is now South Australia. ''Spriggina floundersi'' is the official fossi ...

''.

Fossil record

Imprints of ''Cephalonega stepanovi'' have been found in the Verkhovka and Zimnie Gory Formations of the Ediacaran (Vendian) rocks of the

, 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 A microbial mat is a multi-layered sheet of microorganisms, mainly bacteria and archaea, or bacteria alone. Microbial mats grow at interfaces between different types of material, mostly on submerged or moist surfaces, but a few survive in desert ...

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

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 20 cm are known. The concentric dis ...

'', ''

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 ...

'', Palaeopascichnids, ''

Eoporpita ''Eoporpita'' is a disc or ellipse-shaped Ediacaran fossil with unsure taxonomy/classification. It is known from its type species, ''Eoporpita'' ''medusa'', the only species within the genus ''Eoporpita''. Classification debate/interpretations ...

'', ''

Archaeaspinus ''Archaeaspinus fedonkini'' is an extinct proarticulatan organism from the Late Precambrian (Ediacaran) period. Background ''Archaeaspinus'' was discovered in Zimnii Bereg, the Winter Coast of the White Sea in Russia, by A. Yu. Ivantsov in 2001 ...

'', ''

'', '' Anfesta'', '' Albumares'', '' Tribrachidium'', ''

Kimberella ''Kimberella'' is an extinct 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 gastropods, although its affinity with ...

'', '' Parvancorina'', ''

Charniodiscus ''Charniodiscus'' is an Ediacaran fossil that in life 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 ...

'' and others.

References

{{Taxonbar, from=Q2668806 Proarticulata incertae sedis Fossil taxa described in 1976 Fossils of Russia White Sea fossils Ediacaran life Controversial taxa

Name

Morphology

Fossil record

See also

References