Onega (genus)

Onega Temporal range: Ediacaran
Scientific classification
Kingdom:	Animalia
Phylum:	Proarticulata
Genus:	Onega
Species:	O. stepanovi Fedonkin 1976 [1]

Onega stepanovi is one of the lesser known^[2] fossil taxa from the Ediacaran Period. It was described by Mikhail A. Fedonkin in 1976^[1] and was placed in the Phylum Proarticulata in 1985.^[3][4] It was named after the Onega Peninsula in Russia's White Sea, 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.^[5]

Morphology

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 Onega is covered with small tubercles.^[4]

Onega 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^[3], in which he placed: Onega, Dickinsonia, Palaeoplatoda, Vendia, 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.^[3][6]

Andrey Yu. Ivantsov has proposed that Onega be placed in phylum Proarticulata, as the segments in recently discovered, exceptionally well-preserved fossils display the glide, or "staggered", symmetry characteristic of the majority of proarticulatans.^[4]

Research in progress by A. Yu. Ivantsov denies the presence of the "rigid dorsal carpace" М. Fedonkin observes in Onega and other protarticulatans.^[7].

Fossil record

Imprints of Onega stepanovi have been found in the Verkhovka and Zimnie Gory Formations^{[8] [9]} of the Ediacaran (Vendian) rocks of the Arkhangelsk Region, Russia.^[4]

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.

See also

List of Ediacaran genera

References

1. ^ ^{a b c} B. M. Keller and M. A. Fedonkin (1976). "New Records of Fossils in the Valdaian Group of the Precambrian on the Syuz’ma River" (in Russian) (PDF). Izv. Akad. Nauk SSSR, Ser. Geol. 3: 38–44. http://vend.paleo.ru/pub/Keller_Fedonkin_1976.pdf. 
2. ^ Olson, Everett C. (December 1981). "The Problem of Missing Links: Today and Yesterday". The Quarterly Review of Biology 56 (4): 405–442. doi:10.1086/412432. PMID 7031749. 
3. ^ ^{a b c} M. A. Fedonkin (1985). "Systematic Description of Vendian Metazoa". Vendian System: Historical–Geological and Paleontological Foundation, Vol. 1: Paleontology. Moscow: Nauka, pp. 70–106.
4. ^ ^{a b c d} Ivantsov, A. Yu. (April, 2007). "Small Vendian transversely Articulated fossils". Paleontological Journal 41 (2): 113. doi:10.1134/S0031030107020013. http://www.springerlink.com/content/t213x0g55k650142/. 
5. ^ Keller, B. M.; Menner, V. V.; Stepanov, V. A. and Chumakov, N. M. (1974). "New Finds of Metazoa in the Vendomii of the Russian Platform" (in Russian) (PDF). Izv. Akad. Nauk SSSR, Ser. Geol. 12: 130–134. http://vend.paleo.ru/pub/Keller_et_al_1974.pdf. 
6. ^ 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.
7. ^ M. A. Fedonkin (2003). "The origin of the Metazoa in the light of the Proterozoic fossil record" (PDF). Paleontological Research 7 (1): 9–41. doi:10.2517/prpsj.7.9. http://www.bionet.nsc.ru/live/ppt/Fedonkin_2003.pdf. 
8. ^ D. V. Grazhdankin (2003). "The Structure and Sedimentation Conditions in the Vendian assemblage in the Southeastern White Sea" (PDF). Stratigraphy and Geological Correlation 11 (4): 313–331. http://www.vend.paleo.ru/pub/Grazhdankin%202003.pdf. 
9. ^ D. V. Grazhdankin (2004). "Patterns of distribution in the Ediacaran biotas: facies versus biogeography and evolution" (PDF). Paleobiology 30 (2): 203–221. doi:10.1666/0094-8373(2004)030<0203:PODITE>2.0.CO;2. http://www.vend.paleo.ru/pub/Grazhdankin_2004.pdf. 
10. ^ Gehling, J. G. (1999). "Microbial mats in terminal Proterozoic siliciclastics: Ediacaran death masks". PALAIOS 14 (1): 40–57. doi:10.2307/3515360. http://palaios.geoscienceworld.org/cgi/content/abstract/14/1/40.