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Abyssal: added Category:Paleontology in Quebec using HotCat

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{{Taxobox
| fossil_range = {{Geological range|Ordovician}}
| image = Sphaeragnostus cingulatus linedrawing.jpg
| image_upright = 0.5
| image_caption = ''Sphaeragnostus cingulatus'', linedrawing
| regnum = [[Animal]]ia
| phylum = [[Arthropod]]a
| classis = [[Trilobita]]
| ordo = [[Agnostida]]
| familia = '''Sphaeragnostidae'''
| familia_authority = Kobayashi, 1939
| genus = '''''Sphaeragnostus'''''
| genus_authority = Howell & Resser in Cooper & Kindle, 1936
| subdivision_ranks = [[Species]]
| subdivision =
* ''S. similaris'' (Barrande, 1872) ([[Type (biology)|Type]]) synonym ''Agnostus similaris''
* ''S. cingulatus'' (Olin, 1906) synonym ''Agnostus cingulatus'', ''S. cerus'', ''S. gaspensis europeensis'', ''S. subcircularis''<ref name='Ahlberg'>{{cite journal|last=Ahlberg|first=P.|year=1989|title=Agnostid trilobites from the Upper Ordovician of Sweden and Bornholm, Denmark|journal= Bulletin of the Geological Society of Denmark|volume= 37|pages= 213–226|url= http://2dgf.dk/xpdf/bull37_03-04-213-226.pdf}}</ref>
* ''S. gaspensis gaspensis'' Howell & Resser in Cooper & Kindle, 1936
* ''S. gaspensis quxianensis'' Ju in Qiu et al, 1983
* ''S. nudatus'' Koroleva, 1982
* ''S. orientalis'' Petrunina
}}

'''''Sphaeragnostus''''' is an [[extinct]] [[genus]] from a well-known class of [[fossil]] marine [[arthropod]]s, the [[trilobite]]s. It can be recognized by having two thorax segments, a totally effaced headshield (or cephalon), while the tailshield (or pygidium) although effaced, has a clear furrow parallel to its border, and a short, convex, subcircular axis. It lived during the Ordovician (upper [[Tremadocian|Tremadoc]] to [[Ashgill]]).<ref name="Treatise">Whittington, H. B. et al. Part O, Treatise on Invertebrate Paleontology. Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida. 1997</ref>

== Taxonomy ==
It is difficult to relate ''Sphaeragnostus'' to other agnostids, and it is undecided whether this genus should be assigned to the Agnostoidea, the Condylopygoidea, or a new monotypic superfamily.<ref name='Ahlberg'/>

== Distribution ==
* ''S. similaris'' has been found in the Middle Ordovian of the Czech Republic (Llandeilo of Bohemia, Dobrotivå Formation).
* ''S. cingulatus'' is known from the Upper Ordovician of Sweden (Koången, Lindegård near Lund, and Scania, Jerrestad Mudstone Formation), Denmark (Vasegård, Læså, Bornholm, Jerrestad Mudstone), Poland (Brzezinki) and China (Katian of Jiangxi, western Zhejiang and Subei, Gansu).
* ''S. gaspensis'' was collected from the Upper Ordovician of Canada (Grande Coupe beds, Percé, Quebec)
* ''S. nudatus'' has been excavated from the Upper Ordovician of Kazakhstan (lower Majlisor horizon, Caradoc).<ref name='Ahlberg'/>

== Description ==
Like all Agnostida, ''Sphaeragnostus'' is diminutive and the [[Cephalon (arthropod head)#Trilobites|cephalon]] and [[pygidium]] are of approximately the same size and outline (or isopygious). Like all Agnostina, Sphaeragnostus has only two [[Trilobite#Thorax|thorax]] segments. The cephalon is externally totally effaced and lacks border furrows, axial furrows, and the glabellar node. The pleural regions of thorax segments are very small, while the axis is very wide (perpendicular to the midline) and remarkably short (along the axis). The pygidium has well-defined border furrows and narrow borders. Axial furrows define a short, broad, convex, subcircular, and unfurrowed axis, that bears both axial and terminal nodes. It lacks a median postaxial furrow. If there are spines on the ”rear corners” of the pygidium, these are minute.<ref name="Treatise"/>

=== Differences with Leiagnostus ===
Cephalons of ''Sphaeragnostus'' are extremely effaced and look much like ''[[Leiagnostus]]'' species. Pygidia of ''Sphaeragnostus'' however, differ from other highly effaced genera in a smooth but easily recognizable subcircular axis.

==References ==
{{Reflist}}

[[Category:Agnostida]]
[[Category:Ordovician trilobites]]
[[Category:Fossils of Canada]]
[[Category:Fossils of the Czech Republic]]
[[Category:Fossils of Poland]]
[[Category:Fossils of Denmark]]
[[Category:Fossils of Sweden]]
[[Category:Fossils of Kazakhstan]]
[[Category:Fossils of China]]
[[Category:Paleontology in Quebec]]

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Sphaeragnostus - Revision history

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Abyssal: added Category:Paleontology in Quebec using HotCat