Shankouclava
{{Short description|Extinct genus of tunicate}}
{{Italic title}}
{{Automatic taxobox
| name = Shankouclava
| fossil_range = Cambrian Stage 3, {{fossil range|518|ref={{Cite journal|last1=Yang|first1=C.|last2=Li|first2=X.-H.|last3=Zhu|first3=M.|last4=Condon|first4=D. J.|last5=Chen|first5=J.|date=2018|title=Geochronological constraint on the Cambrian Chengjiang biota, South China|journal=Journal of the Geological Society|language=en|volume=175|issue=4|pages=659–666|doi=10.1144/jgs2017-103|bibcode=2018JGSoc.175..659Y|s2cid=135091168|issn=0016-7649|url=http://nora.nerc.ac.uk/id/eprint/521412/1/2018-JGS-Chuan%20Yang%20et%20al.pdf}}}}
| image = Shankouclava anningense.jpg
| image_upright = 0.7
| image_caption = Restoration of S. anningense.
| taxon = Shankouclava
| authority = Chen et al., 2003
| type_species = †Shankouclava anningense
| type_species_authority = Chen et al., 2003
| subdivision_ranks = Species
| subdivision =
- †S. anningense Chen et al., 2003
- †S. shankouense Chen et al., 2003
}}
Shankouclava is an extinct genus of tunicates. It is one of two{{cite journal|last1=Janvier |first1=Philippe |date=April 23, 2015 |title=Facts and fancies about early fossil chordates and vertebrates |journal=Nature |volume=520 |pages=483–89 |doi=10.1038/nature14437}}{{cite journal|last1=Northcutt |first1=R. Glenn |date=June 26, 2012 |title=Evolution of centralized nervous systems: Two schools of evolutionary thought |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=109 |issue=Supplement 1: In the Light of Evolution VI: Brain and Behavior |pages=10626–10633 |jstor=41601648}} candidates for the oldest member of this group, dating to {{Ma|Chengjiang}}. It has been found in the Lower Cambrian Maotianshan Shale at Shankou village, Anning, near Kunming (South China). Each of the eight specimens found and used for description were isolated, suggesting that the genus was solitary and not colonial.{{cite journal|author1=Chen, Jun-Yuan |author2=Huang, Di-Ying |author3=Peng, Qing-Qing |author4=Chi, Hui-Mei |author5=Wang, Xiu-Qiang |author6=Feng, Man |year=2003 |title=The first tunicate from the Early Cambrian of South China |journal=Proceedings of the National Academy of Sciences |volume=100 |pmid=12835415 |issue=14 |pages=8314–8318 |pmc=166226 |doi=10.1073/pnas.1431177100 |bibcode=2003PNAS..100.8314C |doi-access=free }}
Morphology
Etymology
The generic name is composed of the fossil locality, Shankou, and the Latin word clava (club-shaped).
Classification
A stem group tunicate affinity for Shankouclava has been broadly accepted,{{citation needed|date=December 2024|reason=Expansive claim requires support of some sort}} though some authors have expressed reservations that the evidence in favour of this affinity is not conclusive.{{Cite journal | last = Conway Morris|doi=10.1098/rstb.2006.1846 | pmid = 16754615 | title = Darwin's dilemma: the realities of the Cambrian 'explosion'|journal= Philos Trans R Soc Lond B Biol Sci|date=29 June 2006 |volume=361|number=1470|pages=1069–1083 |pmc=1578734 }}
Doubts regarding Shankouclava's tunicate affinities arose in the context of a long-running debate that began when the paper announcing Shankouclava disputed the tunicate affinities of Cheungkongella, which was known from a single fossil discovered in 2001, and proposed that Cheungkongella is the junior synonym of Phlogites.{{cite book|last1=Gee |first1=Henry |date=July 4, 2018 |chapter=Tunicates |title=Across the Bridge: Understanding the Origin of Vertebrates |pages=85–99 |publisher=University of Chicago Press |isbn=978-0226402864}} This challenge relied on characteristics of newly-discovered Phlogites specimens despite the lack of obvious tentacles. A response several years later similarly questioned Shankouclava by way of new Shankouclava-like specimens that clearly display tentacles.{{Cite journal | last = Shu | url = https://www.sciencedirect.com/science/article/abs/pii/S1342937X07001694 | title = Cambrian explosion: Birth of tree of animals | year = 2008 | journal = Gondwana Research| volume = 14 | issue = 1–2 | pages = 219–240 | doi = 10.1016/j.gr.2007.08.004 | bibcode = 2008GondR..14..219S }} While Shankouclava has not been equated with Phlogites, the presence of Phlogites-like tentacles would make a tunicate affinity unlikely.{{Cite journal | doi = 10.1098/rspb.2009.0646| title = The earliest history of the deuterostomes: The importance of the Chengjiang Fossil-Lagerstätte| year = 2010| last1 = Shu| first1 = D.-G.| last2 = Conway Morris| first2 = S.| last3 = Zhang| first3 = Z.-F.| last4 = Han| first4 = J.| journal = Proceedings of the Royal Society B: Biological Sciences| volume = 277| issue = 1679| pages = 165–174| pmid = 19439437| pmc = 2842668}}
Another Cambrian tunicate, Megasiphon, known from a single specimen from the slightly younger Marjum Formation, resembles more closely the morphology of surviving tunicates.{{Cite journal | doi = 10.1038/s41467-023-39012-4| title = A mid-Cambrian tunicate and the deep origin of the ascidiacean body plan| year = 2023| last1 = Nanglu| first1 = Karma| last2 = Lerosey-Aubril| first2 = Rudy| last3 = Weaver| first3 = James C.| last4 = Ortega-Hernández| first4 = Javier| journal = Nature Communications| volume = 14| issue = 1| page = 3832| pmid = 37414759| pmc = 10325964}}
References
{{Reflist}}
{{Tunicata|F.}}
{{Taxonbar|from=Q55633006}}
Category:Prehistoric chordate genera