Edrioasteroidea is an extinct
class
Class, Classes, 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 d ...
of
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. 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
hardground
Carbonate hardgrounds are surfaces of synsedimentarily cemented carbonate layers that have been exposed on the seafloor (Wilson and Palmer, 1992). A hardground is essentially, then, a lithified seafloor. Ancient hardgrounds are found in limeston ...
s or
brachiopod
Brachiopods (), phylum (biology), phylum Brachiopoda, are a phylum of animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear e ...
s). A 507 million years old species, ''Totiglobus spencensis'', is actually the first known echinoderm adapted to live on a hard surface after the soft microbial mats that covered the seafloor were destroyed in the
Cambrian substrate revolution.
The oldest undisputed fossils of Edrioasteroidea are known from
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 ...
(
Stage 3, about 515-520
Ma ago) of
Laurentia
Laurentia or the North American craton is a large continental craton that forms the Geology of North America, ancient geological core of North America. Many times in its past, Laurentia has been a separate continent, as it is now in the form of ...
and are among the oldest known fossils of echinoderms. Some authors propose that an enigmatic
Ediacaran
The Ediacaran ( ) is a geological period of the Neoproterozoic geologic era, Era that spans 96 million years from the end of the Cryogenian Period at 635 Million years ago, Mya to the beginning of the Cambrian Period at 538.8 Mya. It is the last ...
(about 600 Ma) organism ''
Arkarua'' is also an edrioasteroid, but this interpretation did not gain wide acceptance.
[ Last edrioasteroids are known from ]Permian
The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...
(Late Kungurian, about 270-280 Ma).[
]
Anatomy
The body plan for this class was simple: a main body (theca
In biology, a theca (: thecae) is a sheath or a covering.
Botany
In botany, the theca is related to plant's flower anatomy. The theca of an angiosperm consists of a pair of microsporangia that are adjacent to each other and share a common ar ...
), composed of many small plates, with a peripheral rim for attachment, and (in some species) a ''pedunculate zone'' for extension and retraction. Circling and sometimes attached to the body was a peripheral rim of plates. The main feature consisted of five arms, or ambulacra, in the body wall radiating outwards from the central mouth. The ambulacra grew either curved or straight. When curved, they may all turn in the same direction or else one or two on the right side will curve opposite the others. The ambulacra are built of underlying floor plates that form the food groove and protective cover plates that roof the food groove. The anus
In mammals, invertebrates and most fish, the anus (: anuses or ani; from Latin, 'ring' or 'circle') is the external body orifice at the ''exit'' end of the digestive tract (bowel), i.e. the opposite end from the mouth. Its function is to facil ...
was under the mouth region and was made of small triangular plates to form a cone-shaped area. The bottom surface of the theca is unplated.
Edrioasteroid species are distinguished by differences in the ambulacral curvature, the relationships of the cover plates, and ornamentation. The mode of life was sessile; they were often attached via a stalk made of small plates to a hard object such as a carbonate hardground or shell. Several examples of epibiotic attachment have also been noted.
In the discocystinids, the area between the body and peripheral rim could be extended and retracted; in so doing the two were separated. The peripheral rim became the base of the stalk which was attached to a surface. Underneath the body was a ''recumbent zone'', which was about wide in the genus ''Giganticlavus'', followed by the pedunculate zone attached to the peripheral rim of .[Sumrall 1996]
Taxonomy
List of genera
A very incomplete list of some genera.
*'' Walcottidiscus'' (oldest undisputed edrioasteroid, from the Middle Cambrian 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 ...
community)
**''W. typicallis''
**''W. magister''
*'' Stromatocystites''
**''S. pentangularis''
**''S. reduncus''
**''S. walcotti''
*'' Kailidiscus''
**''K. chinensis''
*'' Edrioaster'' (type genus
In biological taxonomy, the type genus (''genus typica'') is the genus which defines a biological family and the root of the family name.
Zoological nomenclature
According to the International Code of Zoological Nomenclature, "The name-bearin ...
)
**''E. bigsbyi''
**''E. priscus''
*'' Edriophus''
**''E. levis''
*'' Paredriophus''
**''P. elongatus''
*'' Totiglobus''
**''T. nimius''
**''T. lloydi''
*'' Cambraster''
**''C. cannati''
**''C. tastudorum''
*'' Edriodiscus''
**''E. primotica''
*'' Lebedodiscus''
*'' Foerstediscus''
**''F. grandi''
**''F. splendens''
*'' Cystaster''
**''C. stellatus''
*'' Cryptogoleus''
**''C. chapmani''
*'' Bellochthus''
*'' Streptaster''
**''S. vorticellatus''
*'' Cryptogoleus''
**''C. chapmani''
*'' Carneyella''
**''C. pilea''
**''C. faberi''
**''C. ulrichi''
*'' Isorophus''
**''I. cincinnatiensis''
*'' Isorophusella''
*'' Camptostroma''
*''**C. roddyi''
*'' Rectitriordo''
*'' Agelacrinites''
*'' Krama''
**''K. devonicum'' (Bassler), 1936
*''Parakrama''
*'' Hemicystites''
**''H. bohemica''
**''H. chapmani''
**''H. devonicus''
*'' Neoisorophusella''
**''N. lanei''
**''N. berryi''
**''N. maslennikovi''
**''N. whitesidei''
*'' Curvitriordo''
*'' Thresherodiscus''
**''T. ramosa'' (Foerste, 1914)
*'' Postibulla''
**''P. westergaardi''
*'' Parapostibulla''
**''P. belli''
**''P. graysoni''
*'' Eopostibulla''
*'' Pyrgopostibulla''
*'' Yorkicystis''
*'' Torquerisediscus''
*'' Cooperidiscus''
*'' Dynocystis''
*'' Stalticodiscus''
*'' Ulrichidiscus''
*'' Clavidiscus''
*'' Discocystis''
*'' Hypsiclavus''
*'' Spiraclavus''
*'' Giganticlavus''
*'' Lispidecodus''
**''L. plinthotus'' (Kesling, 1967)
Gallery
File:Edrioasteroid_Smithsonian.JPG, ''Foerstediscus splendens''
Image:OrdovicianEdrio.jpg, The Upper Ordovician
The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...
edrioasteroid ''Cystaster stellatus'' on a cobble from the Kope Formation in northern Kentucky. In the background is the cyclostome bryozoan
File:Edrioasteroid from the Milwaukee Formation.jpg, Two edrioasteroids, possibly ''Krama'' or ''Agelacrinites'', with dissociated ambulacral plates, from the Devonian
The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...
of Wisconsin
Wisconsin ( ) is a U.S. state, state in the Great Lakes region, Great Lakes region of the Upper Midwest of the United States. It borders Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake Michigan to the east, Michig ...
.
References
External links
All accessed on March 8, 2008.
*http://www.ucmp.berkeley.edu/echinodermata/edrioasteroidea.html University of California, Berkeley.
*http://drydredgers.org/edrio1.htm Compiled by Colin D. Sumrall.
*https://web.archive.org/web/20060830083438/http://www.tulane.edu/~csumral/Abstract ''Spiraclavus nacoensis'', a New Species of Clavate Agelacrinitid Edrioasteroid from Central Arizona by Colin D. Sumrall.
*http://www.science-art.com/image.asp?id=1357 Reconstruction by Emily Damstra.
*http://gsa.confex.com/gsa/2003AM/finalprogram/abstract_65113.htm Geological Society of America.
*https://web.archive.org/web/20060830083430/http://www.tulane.edu/~csumral/morph.html by Colin D. Sumrall
Taxonomy
Mikko's taxonomy
{{Taxonbar, from=Q137569
Cambrian first appearances
Permian extinctions