Arkarua
| Arkarua | ||||
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Reconstruction of Arkarua |
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| Temporal occurrence | ||||
| Ediacarium | ||||
| 560 million years | ||||
| Locations | ||||
| Systematics | ||||
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| Scientific name | ||||
| Arkarua | ||||
| Gehling , 1987 | ||||
| species | ||||
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Arkarua is an extinct animal species of Ediacariums , which may be a precursor of echinoderms was (Echinodermata).
Etymology and first description
The generic name Arkarua is the Latin feminine of Arkaru , a gigantic, mythical serpent creature of the Adnyamathanha , a local Aboriginal tribe . The taxon adami refers to the eldest son Adam of the first descriptor James G. Gehling , who treated it scientifically in 1987.
Occurrence
Arkarua occurrences were previously limited to Australia and only known from the South Australian Rawnsley Quartzite of the Pound Subgroup in the Flinders Range. However, Liu et al. (2013) now report a find from the Moshakov Formation in the Irkineeva Aufbruch in the south of the Siberian platform .
description
Arkarua adami is a very small, disk-like fossil, the plateau-like, central inner part of which protrudes slightly beyond its flat edge, which is occupied by numerous, radially arranged ridges. Its diameter is 3 to 10 millimeters. In the central part, which is flattened at the top, there are five indentations, starting from the center of the disk, reminiscent of arms, which possibly represent an ambulacral system .
Socialization
Arkarua usually occurs with other representatives of the Ediacaran biota , such as:
Taxonomy
All known fossils from Arkarua are imprints that do not allow any conclusions to be drawn about the internal structure of the taxon. A taxonomic classification is therefore problematic. Because of its five-part symmetry, Arkarua was temporarily assigned to the tribe of echinoderms (Echinodermata). Because of its flattened button shape and its five-fold symmetry, it is placed by some paleontologists in the class of Edrioasteroidea .
The assignment to echinoderms is not clear, as Arkarua had no stereom - an essential characteristic ( synapomorphism ) of later Echinodermata, the skeleton of which was made up of this special calcium carbonate .
A comparison with certain archaic echinoderms such as Homalozoa or Helicoplacoidea also casts doubt on this assignment. The latter had a cycle but did not yet have a fivefold symmetry, which is therefore probably only created secondary in the evolution of the echinoderms.
Some experts believe that Arkarua was closer to Radial Precambrian taxa like Tribrachidium (although these themselves are sometimes associated with the Echinodermata). Occasionally, membership of the new mouths (Deuterostomia) is rejected and the fossil is regarded as a cnidar or even as an alga .
In spite of everything, Mooi and David consider it very likely that Arkarua was a forerunner of the Edrioasteroidea, which already had a cycle and thus could have established the development of echinoderms before the emergence of the stereom. They interpret the five-fold arms as the ontogenetic formation of the axial skeleton, the flat upper part, however, as the formation of the perforated and the edge area as the formation of the non-perforated outer skeleton.
Individual evidence
- ^ Gehling, JG: Earliest known echinoderm - a new Ediacaran fossil from the Pound Subgroup of South Australia . In: Alcheringa . tape 11 , 1987, pp. 337-345 .
- ^ Liu, AG et al .: First report of a newly discovered Ediacaran biota from the Irkineeva Uplift, East Siberia . In: Newsletters on Stratigraphy . tape 46/2 , 2013, p. 95-110 .
- ^ Paul D. Taylor and David N. Lewis: Fossil Invertebrates . Harvard University Press, 2007, ISBN 0-674-02574-1 , pp. 163-164 .
- ↑ Mooi, R. and David, B .: Evolution within a Bizarre Phylum: Hommologies of the First Echinoderms . In: American Zoologist . tape 38 , 1998, pp. 965-974 .