Editing Arkarua

{{Short description|Precambrian fossil}}
{{Use dmy dates|date=December 2023}}

{{Speciesbox
| fossil_range     = Late [[Ediacaran]], about {{fossil_range|555}}
| image            = Arkarua adami pennetta.png
| image_caption    = [[Paleoart|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&nbsp;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 [[Edrioasteroid]]ea, a [[class (biology)|class]] of the echinoderms.{{Citation needed|date=June 2007}}

This identification remains suspect, as the fossils do not appear to have either [[madreporite]]s, 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)

{{Taxonbar|from1=Q15104336|from2=Q2318649}}

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


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