''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 in 1976

Name

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

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 . Geog ...

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

fossil site This list of fossil sites is a worldwide list of localities known well for the presence of fossils. Some entries in this list are notable for a single, unique find, while others are notable for the large number of fossils found there. Many of ...

on the Letniy Bereg (" Summer Coast") in 1972, on the

, the first Proterozoic site found in the

Arkhangelsk Oblast Arkhangelsk Oblast (russian: Арха́нгельская о́бласть, ''Arkhangelskaya oblast'') is a federal subjects of Russia, federal subject of Russia (an oblast). It includes the Arctic Ocean, Arctic archipelagos of Franz Josef Land ...

. The original generic name is previously occupied by the

hemiptera Hemiptera (; ) is an order (biology), order of insects, commonly called true bugs, comprising over 80,000 species within groups such as the cicadas, aphids, planthoppers, leafhoppers, Reduviidae, assassin bugs, Cimex, bed bugs, and shield bugs. ...

n 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 cov ...

'', ''

Praecambridium ''Praecambridium sigillum'' is an extinct organism that superficially resembles a segmented trilobite-like arthropod. It was originally described as being a trilobite-like arthropod, though the majority of experts now place it within the Proartic ...

'' 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 ...

'' 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 C with bar, 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 ...

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 At ...

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 Nomenclature f ...

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'', '' Palaeoplatoda'', ''

'', ''

'' 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 organism '' Parvancorina''. A single specimen ...

''.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 Nomenclature f ...

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. ...

, 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 fo ...

''.

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 deserts ...

s. The same bedding planes contain various other Ediacaran species: '' Cyclomedusa'', '' Ediacaria'', Palaeopascichnids, '' Eoporpita'', ''

'', ''

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 ...

'', ''

'', '' Dickinsonia'', ''

Anfesta ''Anfesta stankovskii'' is a tri-radially symmetrical fossil animal that lived in the late Ediacaran (Vendian) seafloor. It is a member of the extinct group Trilobozoa. Etymology The generic and specific names of the ''Anfesta stankovskii'' ho ...

'', ''

Albumares ''Albumares brunsae'' is a tri-radially symmetrical fossil animal that lived in the late Ediacaran seafloor. It is a member of the extinct group Trilobozoa. Etymology The generic name ''Albumares'' derives from the Latin ''Mare Album'' (White ...

'', ''

Tribrachidium ''Tribrachidium heraldicum'' is a tri-radially symmetric fossil animal that lived in the late Ediacaran (Vendian) seas. In life, it was hemispherical in form. ''T. heraldicum'' is the best known member of the extinct group Trilobozoa. Etymol ...

'', ''

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 t ...

'', ''

Parvancorina ''Parvancorina'' is a genus of shield-shaped bilaterally symmetrical fossil animal that lived in the late Ediacaran seafloor. It has some superficial similarities with the Cambrian trilobite-like arthropods. Etymology The generic name is derived ...

'', ''

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. Th ...

'' 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