| 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]
Contents |
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].
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.