''Arkarua adami'' is a small,

Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...

disk-like

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

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 The Ediacaran Period ( ) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and th ...

beds of the Flinders Ranges in South Australia. The generic name refers to Arkaroo, a giant snake from

the Dreaming The Dreaming, also referred to as Dreamtime, is a term devised by early anthropologists to refer to a religio-cultural worldview attributed to Australian Aboriginal beliefs. It was originally used by Francis Gillen, quickly adopted by his co ...

of the local Aboriginal people.

Classification

All known specimens of ''Arkarua'' are casts that give no clue to the internal structure, making classification problematic. Because of ''Arkaruas pentamerous symmetry, it is tentatively placed within

phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature f ...

Echinodermata An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the sea li ...

. Because of its flattened disk- or button-shape, coupled with its pentamerous symmetry, some claim that it can be further classified into the

Edrioasteroid Edrioasteroidea is an extinct class of echinoderms. The living animal would have resembled a pentamerously symmetrical disc or cushion. They were obligate encrusters and attached themselves to inorganic or biologic hard substrates (frequently har ...

ea, a

class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differentl ...

of the echinoderms. This identification remains suspect, as the fossils do not appear to have either

madreporite The madreporite is a light colored calcareous opening used to filter water into the water vascular system of echinoderms. It acts like a pressure-equalizing valve. It is visible as a small red or yellow button-like structure, looking like a smal ...

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.Paul D. Taylor, David N. Lewis ''Fossil Invertebrates'' Harvard University Press, 2007 pages 163-164

References

External links

Vendian animals: ''Arkarua'' from the Ediacara Hills of Australia
from the University of California Berkeley Museum of Paleontology. (pictures) Ediacaran life Prehistoric invertebrates of Australia Enigmatic prehistoric animal genera Edrioasteroidea {{ediacaran-stub

Classification

See also

References

External links