''Walcottidiscus'' is a genus of

pentagon In geometry, a pentagon () is any five-sided polygon or 5-gon. The sum of the internal angles in a simple polygon, simple pentagon is 540°. A pentagon may be simple or list of self-intersecting polygons, self-intersecting. A self-intersecting ...

ally shaped

echinoderm An echinoderm () is any animal of the phylum Echinodermata (), which includes starfish, brittle stars, sea urchins, sand dollars and sea cucumbers, as well as the sessile sea lilies or "stone lilies". While bilaterally symmetrical as ...

s known from the Middle

Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...

Burgess Shale The Burgess Shale is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the exceptional preservation of the soft parts of its fossils. At old (middle Cambrian), it is one of the earliest fos ...

. 16 specimens of ''Walcottidiscus'' are known from the Greater Phyllopod bed, where they comprise < 0.1% of the community. The genus is thought to be the earliest known, more or less undisputed edrioasteroid. The pentamerous '' Arkarua'' is older, dating from the late

Precambrian The Precambrian ( ; or pre-Cambrian, sometimes abbreviated pC, 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 t ...

, but with existing fossils of this organism showing no evidence of having stereoms, its status as an edrioasteroid echinoderm remains under much discussion. There are two species of ''Walcottidiscus'' recognized, each known from a single, poorly preserved fossil specimen. ''W. typicallis'' is known from the smaller specimen, and ''W. magister'' is known from the larger specimen. Many experts suggest that ''W. magister'' actually represents a large specimen of ''W. typicallis'', but more, better preserved specimens are needed to verify this hypothesis.

References

External links

* Burgess Shale fossils Edrioasteroidea Prehistoric Crinozoa genera {{paleo-echinoderm-stub