{{Short description|Extinct genus of trilobites}} {{Automatic taxobox | fossil_range = {{fossil range|522|510|Late Atdabanian-Botomian}} | image = Yunnanocephalus S CRF.jpg | image_caption = ''Yunnanocephalus yunnanensis'', {{convert|18|mm|in|abbr=on}} | taxon = Yunnanocephalus | authority = Kobayashi, 1936 | type_species = ''Ptychoparia yunnanensis'' | subdivision_ranks = Species | subdivision = {{Species list |Yunnanocephalus yunnanensis|(Mansuy, 1912) |Yunnanocephalus longioccipitalis|Palmer & Rowell, 1995 |Yunnanocephalus macromelos|Paterson & Brock, 2007 }} | synonyms = *''Pseudoptychoparia'' }}
'''''Yunnanocephalus''''' is a genus of ptychopariid trilobite. It lived during the late Atdabanian and Botomian stages, in what are currently Antarctica, Australia and China. It was a "moderately common" member of the Chengjiang Fauna.<ref name="Sepkoski">{{cite journal|last=Sepkoski |first=Jack |title=A compendium of fossil marine animal genera (Trilobita entry) |journal=Bulletins of American Paleontology |volume=364 |page=560 |year=2002 |url=http://strata.ummp.lsa.umich.edu/jack/showgenera.php?taxon=307&rank=class |access-date=2008-01-08 |url-status=dead |archive-url=https://web.archive.org/web/20060905162524/http://strata.ummp.lsa.umich.edu/jack/showgenera.php?taxon=307&rank=class |archive-date=September 5, 2006 }}</ref>
== Description == ''Yunnanocephalus'' is a small (about {{convert|2|cm|in|disp=or}}) trilobite with an inverted elongated egg-shaped outline. Its headshield (or cephalon) is ovate and twice as wide as long, slightly wider than and not confluent with the articulate middle part of the exoskeleton (or thorax). The raised central section (or glabella) is weakly defined, without clear furrows except for one defining the occipital ring, tapering forward, with the front straight and confluent with the eye ridges. The occipital ring is about as wide as the border and the axial rings of the thorax. The distance between the glabella and the frontal border is slightly wider that the border. The visual surface of the eye is rather small (about 20% of the length of the cephalon), with the front about halflength of the cephalon. The natural rupture line (or suture) anterior of the visual surface is parallel to the midline or converges slightly forward and from the back of the eye diverges to the middle of the widely rounded back edges of the cephalon. The thorax has 14 segments, with short triangular spines, the 3rd and 4th slightly wider than the frontal segments, and a small tailshield (or pygidium) consisting almost fully of the axis and post axial boss, with two vaguely defined axial rings.<ref>{{Cite book |last1= Guang|first1= Hou Xian|last2= Aldridge|first2=Richard J.|author-link2=Richard Aldridge|last3=Bergstrom|first3=Jan|last4=Siveter|first4=David J.|last5=Siveter|first5=Derek J.|last6=Xian-Hong|first6=Feng|year=2004|title= The Cambrian Fossils of Chengjiang, China: The Flowering of Early Animal Life|location= Oxford, U.K.|publisher= Blackwell Publishing|isbn= 1-4051-0673-5}}</ref>
== Ontogeny == During the ontogenetic development of ''Y. yunnanensis'' between a late larval phase (meraspis degree 9, 2½mm) and the adult (or holaspis) the facial suture changes from proparian to gonatoparian. Although this development has also been observed in ''Duyunaspis duyunensis'', it is really uncommon. Usually, proparian holaspid trilobites developed from opisthoparian meraspids due to a mechanism called heterochrony.<ref>{{cite journal|last1= Dai|first1= T.|last2= Zhang|first2= X.|year= 2008|title= Ontogeny of the trilobite ''Yunnanocephalus yunnanensis'' from the Chengjiang lagerstätte, lower Cambrian, southwest China|journal= Alcheringa|volume= 32|issue= 4|pages= 465–468|issn= 0311-5518|doi=10.1080/03115510802418057|bibcode= 2008Alch...32..465D|s2cid= 129582955}}</ref>
== Distribution == * ''Y. longioccipitalis'' is known from the Lower Cambrian of Antarctica (Atdabanian, Shackleton Limestone, 81.9° S, 158.7° E).<ref>{{cite journal|last1= Palmer|first1= A.R.|last2= Rowell|first2= A.J.|year= 1995|title= Early Cambrian trilobites from the Shackleton Limestone of the Central Mountains|journal= Journal of Paleontology|volume= 69|issue= 6|pages= 1–28|doi= 10.1017/S0022336000061424|bibcode= 1995JPal...69S...1P|s2cid= 182206675}} ''cited on'' {{cite journal|author= Shanan Peters|journal= Fossilworks|title= Shackleton Limestone; H-84 collections|jstor= 1315607}}</ref> * ''Y. macromelos'' has been found in the Lower Cambrian of Australia (Botomian, Mernmerna Formation, Angorichina station, east side of The Bunkers, 1 km S Balcoracana Creek, South-Australia, 31.2° S, 138.9° E).<ref>{{cite journal|last1= Brock|first1= G.A.|last2= Patterson|first2= J.R.|year= 2004|title= A new species of ''Tannuella'' (Helcionellida, Mollusca) from the Early Cambrian of South Australia|journal= Memoirs of the Association of Australasian Palaeontologists|volume= 30|pages=133–143}} ''cited on'' {{cite web|author= Pete Wagner|website= fossilworks|title= MMF/58.3. Angorichina station, east side of The Bunkers, 1 km S Balcoracana Cr.|url= https://paleobiodb.org/classic/displayCollResults?collection_no=67980|access-date= 17 December 2021}}</ref> * ''Y. yunnanensis'' occurs in the Lower Cambrian of China (Atdabanian, Yuanshan or Qiongzhusi Formation, Chengjiang biota, near Haikou, Anning, Jinning, Jingmacun, Kunming, Yunnan, 24.8° N, 102.6° E;<ref>{{cite journal|last1= Steiner|first1= M.|last2= Zhu|first2= M.|last3= Zhao|first3= Y.|last4= Erdtmann|first4= B.-D.|year= 2005|title= Lower Cambrian Burgess Shale-type fossil associations of South China|journal= Palaeogeography, Palaeoclimatology, Palaeoecology|volume= 220|issue= 1–2|pages= 129–152|doi=10.1016/j.palaeo.2003.06.001|bibcode= 2005PPP...220..129S}} ''cited on'' {{cite web|author= John Alroy|website= fossilworks|title= Haikou [Yuanshan Fm (formerly Qiongzhusi)]|url= https://paleobiodb.org/classic/displayCollResults?collection_no=68083|access-date= 17 December 2021}}</ref> and Maotianshan Bed 4, 24.0° N, 102.0° E).<ref>{{cite journal|last1= Yugan|first1= J.|last2= Xianguang|first2= H.|last3= Huayu|first3= W.|year= 1993|title= Lower Cambrian pediculate lingulids from Yunnan, China|journal= Journal of Paleontology|volume= 67|issue= 5|pages= 788–798|doi= 10.1017/S0022336000037057|bibcode= 1993JPal...67..788Y|s2cid= 131913237}} ''cited on'' {{cite web|author= Austin Hendy|website= fossilworks|title= Maotianshan, Bed 4 [Yuanshan Fm]|url= https://paleobiodb.org/classic/displayCollResults?collection_no=90494|access-date= 17 December 2021}}</ref>
== References == {{Reflist|30em}}
== External links == * [http://www.trilobites.info/ordptychopariida.htm Order Pitychopariida at trilobite.info]
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Category:Ellipsocephaloidea Category:Ptychopariida genera Category:Cambrian trilobites Category:Trilobites of Antarctica Category:Cambrian trilobites of Australia Category:Cambrian trilobites of Asia Category:Fossils of China Category:Fossil taxa described in 1936 Category:Cambrian genus extinctions