Arkarua

{{Speciesbox | fossil_range = Late Ediacaran, about {{fossil_range|555}} | image = Arkarua adami pennetta.png | image_caption = Artist's restoration | genus = Arkarua | parent_authority = Gehling, 1987 | species = adami | authority = Gehling, 1987 }}

'''''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 five small dots from the middle of the disk center. Fossils range from 3 to 10 mm in diameter.

''Arkarua'' is known only from the Ediacaran beds of the Flinders Ranges in South Australia. The generic name refers to Arkaroo, a giant snake from the Dreaming of the local Aboriginal people.<ref>{{cite journal|last=Gehling|first=J.G.|year=1987|title=Earliest known echinoderm — a new Ediacaran fossil from the Pound Subgroup of South Australia|journal=Alcheringa|volume=11|pages=337–345|doi=10.1080/03115518708619143}}</ref>

''Arkarua'' is suggested to have been a passive suspension feeder.<ref>{{cite web|url=https://blogs.adelaide.edu.au/environment/2021/04/06/555-million-year-old-fossils-reveal-early-feeding-strategies/|title=555 million-year-old fossils reveal early feeding strategies|last=García-Bellido|first=Diego C.|date=6 April 2021|website=Environment Institute Blog|publisher=The University of Adelaide|access-date=29 December 2023|archive-date=29 December 2023|archive-url=https://web.archive.org/web/20231229011958/https://blogs.adelaide.edu.au/environment/2021/04/06/555-million-year-old-fossils-reveal-early-feeding-strategies/|url-status=live}}</ref>

==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.{{Citation needed|date=June 2007}}

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.<ref>{{cite book|first1=Paul D.|last1=Taylor|first2=David N.|last2=Lewis|title=Fossil Invertebrates|publisher=Harvard University Press|year=2007|isbn=0-674-02574-1|pages=163–164}}</ref>

==See also== * List of Ediacaran genera

==References== {{Reflist}} * {{cite book | author = McMenamin M. | year = 1986 | title = The Garden of Ediacara | volume = | publisher = Columbia University Press | isbn = 978-0-231-10559-0 |url=http://www.earthscape.org/r3/mcm02/mcm02k.pdf | accessdate = 8 March 2007 }}{{Dead link|date=May 2019 |bot=InternetArchiveBot |fix-attempted=yes }}

== External links == * [http://www.ucmp.berkeley.edu/vendian/arkarua.html Vendian animals: ''Arkarua'' from the Ediacara Hills of Australia], from the University of California Berkeley Museum of Paleontology. (pictures)

Category:Ediacaran life Category:Prehistoric invertebrates of Australia Category:Enigmatic prehistoric animal genera Category:Edrioasteroidea Category:Monotypic prehistoric animal genera