Edrioasteroidea is an extinct
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
echinoderm
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 ...
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 limestone ...
s or
brachiopod
Brachiopods (), phylum Brachiopoda, are a phylum of trochozoan 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 end, w ...
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 "Cambrian substrate revolution" or "Agronomic revolution", evidenced in trace fossils, is the diversification of animal burrowing during the early Cambrian period.
Before this "widening of the behavioural repertoire", bottom-dwelling anima ...
.
The oldest undisputed fossils of Edrioasteroidea are known from
Cambrian
The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...
(
Stage 3
Stage or stages may refer to:
Acting
* Stage (theatre), a space for the performance of theatrical productions
* Theatre, a branch of the performing arts, often referred to as "the stage"
* ''The Stage'', a weekly British theatre newspaper
* St ...
, about 515-520
Ma ago) of
Laurentia
Laurentia or the North American Craton is a large continental craton that forms the 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 North America, although ...
and are among the oldest known fossils of echinoderms. Some authors propose that an enigmatic
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 ...
(about 600 Ma) organism ''
Arkarua
''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 ...
'' 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 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 251.9 Mya. It is the last period of the Paleoz ...
(Late Kungurian
In the geologic timescale, the Kungurian is an age or stage of the Permian. It is the latest or upper of four subdivisions of the Cisuralian Epoch or Series. The Kungurian lasted between and million years ago (Ma). It was preceded by the Artin ...
, about 270-280 Ma).[
]
Anatomy
The body plan for this class was simple: a main body (theca
In biology, a theca (plural 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 commo ...
), 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
Ambulacrum is an architectural word that denotes an atrium, courtyard, or parvise in front of a basilica or church that is surrounded by arcades or colonnades, or trees, and which often contains a fountain
A fountain, from the Latin "fon ...
, 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
The anus (Latin, 'ring' or 'circle') is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, the residual semi-solid waste that remains after food digestion, which, d ...
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
Sessility, or sessile, may refer to:
* Sessility (motility), organisms which are not able to move about
* Sessility (botany), flowers or leaves that grow directly from the stem or peduncle of a plant
* Sessility (medicine), tumors and polyps that ...
; they were often attached via a stalk made of small plates to a hard object such as a carbonate 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 limestone ...
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.
*?''Arkarua
''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 ...
''
**?''A. adami'' (may be a Trilobozoan
''Trilobozoa'' (meaning "three-lobed animals") is a phylum of extinct mobile animals that were originally classified into the Cnidaria. The basic body plan of ''Trilobozoa'' is often a tri-radial or radial sphere-shaped form with lobes radiating ...
with pentamerous symmetry, and not an echinoderm at all)
*''Walcottidiscus
''Walcottidiscus'' is a genus of pentagonally shaped echinoderms known from the Middle Cambrian Burgess Shale. 16 specimens of ''Walcottidiscus'' are known from the Greater Phyllopod bed, where they comprise < 0.1% of the community. '' (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 foss ...
community)
**''W. typicalus''
*''Kailidiscus
''Kailidiscus'' is an extinct genus of echinoderm
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 urchi ...
''
**''K. chinensis''
*'' Edrioaster'' (type genus
In biological taxonomy, the type genus 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-bearing type of a nominal f ...
)
**''E. bigsbyi''
**''E. priscus''
*'' Edriophus''
**''E. levis''
*'' Paredriophus''
**''P. elongatus''
*'' Totiglobus''
**''T. nimius''
**''T. lloydi''
*'' 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
''Isorophus'' is an extinct genus of Echinoderm belonging to the class Edrioasteroidea. It is commonly found in deposits dating to the Ordovician period. There are several species, with one (''Isorophus cincinnatiensis'') being the official fos ...
''
**''I. cincinnatiensis''
*'' Isorophusella''
*''Camptostroma
''Camptostroma roddyi'' is an extinct echinoderm from the ''Bonnia''-''Olenellus'' Zone the Early Cambrian Kinzers Formation near York and Lancaster, Southeastern Pennsylvania. In life, it would have resembled a cupcake, with the axial skeleton ...
''
*''**C. roddyi''
*'' Rectitriordo''
*'' Agelacrinites''
*''Krama
A krama (; km, ក្រមា ) is a sturdy traditional Cambodian garment with many uses, including as a scarf, bandanna, to cover the face, for decorative purposes, and as a hammock for children. It may also be used as a form of weaponry. Bo ...
''
**''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
''Yorkicystis'' is a genus of edrioasteroid echinoderm that lived 510 million years ago in the Cambrian aged Kinzers Formation in what is now Pennsylvania. This genus is important as it provides some of the oldest evidence of echinoderms losing th ...
''
*'' Torquerisediscus''
*'' Cooperidiscus''
*'' Dynocystis''
*'' Stalticodiscus''
*'' Ulrichidiscus''
*'' Clavidiscus''
*'' Discocystis''
*'' Hypsiclavus''
*'' Spiraclavus''
*'' Giganticlavus''
*'' Lispidecodus''
**''L. plinthotus'' (Kesling, 1967)
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
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. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...
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 geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...
of Wisconsin
Wisconsin () is a state in the upper Midwestern United States. Wisconsin is the 25th-largest state by total area and the 20th-most populous. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake M ...
.
{{Taxonbar, from=Q137569
Cambrian first appearances
Permian extinctions