| Cephalonega stepanovi Temporal range: Ediacaran, around | |
|---|---|
 | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | † Proarticulata |
| Class: | † Cephalozoa |
| Genus: | † Cephalonega Ivantsov et al., 2019 |
| Species: | †C. stepanovi |
| Binomial name | |
| †Cephalonega stepanovi (Fedonkin, 1976 [1] ) | |
| Synonyms | |
Onega stepanoviFedonkin, 1976 | |
Cephalonega stepanovi is a fossil organism from Ediacaran deposits of the Arkhangelsk Region, Russia. It was described by Mikhail A. Fedonkin in 1976 [1]
Its original genus name Onega comes from the Onega Peninsula of the White Sea, where the first fossils were found. The species name was given to honour V.A. Stepanov, who discovered the Ediacaran fossil site on the Letniy Bereg ("Summer Coast") in 1972, on the Onega Peninsula, the first Proterozoic site found in the Arkhangelsk Oblast. [2] The original generic name is previously occupied by the hemipteran genus Onega Distant (1908). Ivantsov et al. (2019) coined a replacement generic name Cephalonega. [3] [4]
The small fossils, which range up to 7 millimetres (0.28 in) long, have oval outlines and low bodies with an articulated central zone built of isomers encircled by an undivided zone. The surface of the undivided region of Cephalonega is covered with small tubercles. [5]
Cephalonega was originally described by Mikhail Fedonkin as a problematic organism, being grouped together with Vendia , Praecambridium and Vendomia as possible stem-group arthropods due to a vague similarity with primitive Cambrian trilobites and arthropods. [1]
In 1985 Mikhail Fedonkin erected Phylum Proarticulata, [6] in which he placed: Cephalonega, Dickinsonia , Palaeoplatoda , Vendia , Vendomia , 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 . [6] [7]
Andrey Yu. Ivantsov has proposed that Cephalonega should be placed in the phylum Proarticulata, as the segments in recently discovered, exceptionally well-preserved fossils display the glide, or "staggered", symmetry characteristic of the majority of proarticulatans. [5]
According to a 2019 study, all Cephalonega researchers agree that it is proarticulatan and put it in the class Cephalozoa that also includes e.g. Yorgia , Andiva and Spriggina . [3]
Imprints of Cephalonega stepanovi have been found in the Verkhovka and Zimnie Gory Formations [8] [9] of the Ediacaran (Vendian) rocks of the Arkhangelsk Region, Russia. [5]
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 mats. [10] The same bedding planes contain various other Ediacaran species: Cyclomedusa , Ediacaria , Palaeopascichnids, Eoporpita , Yorgia , Andiva , Archaeaspinus , Vendia , Dickinsonia , Anfesta , Albumares , Tribrachidium , Kimberella , Parvancorina , Charniodiscus and others.
Dickinsonia is a genus of extinct organism, most likely an animal, that lived during the late Ediacaran period in what is now Australia, China, Russia and Ukraine. It is one of the best known members of the Ediacaran biota. The individual Dickinsonia typically resembles a bilaterally symmetrical ribbed oval. Its affinities are presently unknown; its mode of growth has been considered consistent with a stem-group bilaterian affinity, though various other affinities have been proposed. The discovery of cholesterol molecules in fossils of Dickinsonia lends support to the idea that Dickinsonia was an animal, though these results have been questioned.
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 this group is contentious.
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.
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 25 cm (9.8 in). It is classified within the extinct animal phylum Proarticulata.
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 cover the smaller ones externally but the posterior ends of all the isomers remain free. The transverse elements decrease in size from anterior to posterior and are all inclined in the same direction.
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 Proarticulata as a close relative of the much larger Yorgia. It is from the Late Ediacaran deposit of Ediacara Hills, Australia, about 555 million years ago. On average, P. sigillum had at least 5 pairs of segments, with each unit becoming progressively larger as they approach the cephalon-like head.
Ovatoscutum concentricum is one of many enigmatic organisms known from the Ediacaran deposits of the Flinders Ranges, Australia, and the White Sea area in Russia, dating around 555 Ma.
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.
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.
Proarticulata is a proposed phylum of extinct, bilaterally symmetrical animals known from fossils found in the Ediacaran (Vendian) marine deposits, and dates to approximately 567 to 550 million years ago. The name comes from the Greek προ = "before" and Articulata, i.e. prior to animals with true segmentation such as annelids and arthropods. This phylum was established by Mikhail A. Fedonkin in 1985 for such animals as Dickinsonia, Vendia, Cephalonega, Praecambridium and currently many other Proarticulata are described.
Vendiamorpha is a class of extinct animals within the Ediacaran phylum Proarticulata.
Tamga hamulifera is a disk-shaped fossil from Precambrian strata of the White Sea area, in Russia, the only member of the genus Tamga.
Isomer is an element of transverse body articulation of the bilateral fossil animals of the Phylum Proarticulata from the Ediacaran (Vendian) period. This term has been proposed by Andrey Yu. Ivantsov, a Russian paleontologist from the Laboratory of the Precambrian organisms, Paleontological Institute, Russian Academy of Sciences.
Epibaion is a trace fossil imprint of the Ediacaran animals of the phylum Proarticulata, which became extinct in the Precambrian. Imprints often occurring in chains, that is interpreted as a feeding trace; some chains terminate in a body fossil, allowing their maker to be identified. Several specimens are known; E. waggoneris was produced by Yorgia waggoneri; E. costatus by Dickinsonia costata, and E. axiferus, the type species, has as yet not been found with a trace-maker. It is proposed that the Australian fossil Phyllozoon is also a feeding trace of Proarticulata.
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 in a new genus by Mikhail Fedonkin in 2002. It lived about 555 million years ago. Fossils of Andiva also occur in South Australia. All known fossils of Andiva are external molds.
Palaeoplatoda is a genus from the Ediacaran biota. It is a soft-bodied organism with a segmented body that resembles Dickinsonia, another Ediacaran organism.
Archaeaspinus fedonkini is an extinct proarticulatan organism from the Late Precambrian (Ediacaran) period.
Cephalozoa are an extinct class of primitive segmented marine organisms within the Phylum Proarticulata from the Ediacaran period. They possessed bilateral symmetry and were characterized by a thin, rounded body.
Ivovicia is an extinct genus of proarticulates. This monotypic genus has only one species: Ivovicia rugulosa.The genus is named after the Ivovik creek, near the place where the specimen was found.