Parvancorina
| Parvancorina | ||||
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Schematic reconstructions of Parvancorina sagitta and Parvancorina minchami |
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| Ediacarium | ||||
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| Scientific name | ||||
| Parvancorina | ||||
| Glaessner , 1958 | ||||
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Parvancorina is an extinct animal species of uncertain taxonomic classification that lived in the Ediacarian (about 600 million years ago). With its bilateral symmetrical shield it shows similarities to primitive arthropods (Arthropoda).
Etymology and Discovery
The generic name Parvancorina is a Krasis -composition of the Latin words parva (parvus, -a, -um) and ancora meaning 'small anchor'. The species name minchami honors Mr. H. Mincham, a private fossil collector who found some very beautiful pieces in the Ediacara Biota in 1957 and presented them to the South Australian Museum . The species name sagitta of the second taxon is the Latin name for 'arrow'.
Initial descriptions
The genus Parvancorina and the type fossil Parvancorina minchami were first scientifically described in 1958 by Martin F. Glaessner . The taxon Parvancorina sagitta was only edited in 2004 by Andrei Jurjewitsch Iwanzow .
Occurrence
The type fossil Parvancorina minchami was discovered in 1957 in the Ediacara Member des Rawnsley quartzite , which is found in the Flinders Range in South Australia . It also occurs in the Verchowka Formation , the Simnigori Formation, and the Jorga Formation on the White Sea coast in northern Russia ( Arkhangelsk Oblast ). The genus Parvancorina also appears in the Ljamza formation in a rather poor condition .
description
Parvancorina has a relief-like raised back that runs along the central axis of symmetry. This ridge can protrude very clearly in only moderately compacted fossils. At the head or front end of the back, two raised arches are attached to the central back, each of which spans a quarter circle. In front of it lie two lines that separate from the arches and form a semicircle. Tooth-like elevations extend over arches and back towards the inside of the shield.
The nearly circular, shield-like fossils of Parvancorina show a clearly convex profile. They usually measure 10 millimeters in length and width, but can occasionally reach 20 millimeters in length and width. Their smallest representatives are 3 millimeters long and 2 millimeters wide, but large forms reach up to 25 millimeters in length and 21 millimeters in width. Even shapes in which their width of 23 millimeters slightly exceeds their length of 22 millimeters are known.
Taxonomy
The taxonomic position of Parvancorina is uncertain. The fossil has affinities to various primitive, trilobite- like arthropods, for example Skania fragilis from the Burgess Shale Biota in Canada and Primicaris larvaformis from the Chengjiang Biota in the People's Republic of China . For arthropods, however, the growth stage of Parvancorina is very unusual and their sessile way of life cannot be combined with arthropods. Furthermore, an affinity for arthropods is strongly called into question by the great similarity of Parvancorina sagitta to Temnoxa , a primitive, mollusc-like bilaterian.
Habitat and way of life
Parvancorina's position in life was parallel to the current. The organism is likely to have lived on organic suspension. The marginal overfolding of the fossil, which could occur from all directions, speaks against an adherent way of life on the sea floor by means of a stem.
Individual evidence
- ^ Glaessner, Martin F .: New Fossils from the Base of the Cambrian in South Australia . In: Transactions of the Royal Society of South Australia . tape 81 , 1958, pp. 185-188 .
- ^ Glaessner, Martin F. and Wade, Mary: The Late Precambrian Fossils from Ediacara, South Australia . In: Paleontology . tape 9 (4) , 1966, pp. 599-628 .
- ↑ Lin, JP et al: A Parvancorina-like arthropod from the Cambrian of South China . In: Historical Biology . tape 18 (1) , 2006, pp. 33-45 , doi : 10.1080 / 08912960500508689 .
- ↑ Naimark, EB and Ivantsov, A. Yu .: Growth variability in the late Vendian problematics Parvancorina Glaessner . In: Paleontological Journal . tape 43 (1) , 2009, pp. 12-18 , doi : 10.1134 / S003103010901002X .
- ↑ Ivantsov, AY, Malakhovskaya, YE and Serezhnikova, EA: Some Problematic Fossils from the Vendian of the Southeastern White Sea Region . In: Paleontological Journal 38 (1) . 2004, p. 1-9 .
- ↑ Droser, Mary L .: Anchors Away: Anatomy of an Ediacaran sea floor dominated by parvancorina . In: Geological Society of America: Abstracts with Programs . tape 39 (6) , p. 332 .
