Arkarua

Arkarua adami is a small, Precambrian disk-like fossil with a raised center, a number of radial ridges on the rim, and a five-pointed central depression marked with radial lines of 5 small dots from the middle of the disk center. Fossils range from 3 to 10 mm in diameter.

Arkarua
Temporal range: Late Ediacaran, about 555 Ma
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Scientific classification
Kingdom: Animalia
Phylum: Echinodermata (?)
Class: †Edrioasteroidea (?)
Genus: †Arkarua
Gehling, 1987
Species:
†A. adami
Binomial name
†Arkarua adami
Gehling, 1987

Arkarua is known only from the Ediacaran beds of the Flinders Ranges in South Australia. The generic name refers to Arkaru, a mythical giant snake of the local Aboriginal people.[1]

Classification

All known specimens of Arkarua are casts that give no clue to the internal structure, making classification problematic. Because of Arkarua's pentamerous symmetry, it is tentatively placed within phylum Echinodermata. Because of its flattened disk- or button-shape, coupled with its pentamerous symmetry, some claim that it can be further classified into the Edrioasteroidea, a class of the echinoderms.

This identification remains suspect, as the fossils do not appear to have either madreporites, or plates of stereom, a unique crystalline form of calcium carbonate from which echinoderm skeletons are built. These two features are diagnostic of all other echinoderms, as all extinct and extant echinoderms have either one, the other, or both features present.[2]

See also

References
  1. Gehling, J.G. 1987. Earliest known echinoderm — a new Ediacaran fossil from the Pound Subgroup of South Australia. Alcheringa 11:337-345.
  2. Paul D. Taylor, David N. Lewis Fossil Invertebrates Harvard University Press, 2007 ISBN 0-674-02574-1 pages 163-164


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