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Shankouclava
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| Shankouclava Temporal range: Cambrian Stage 3,
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| Restoration of S. anningense. | |
Scientific classification 
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| Kingdom: | Animalia |
| Phylum: | Chordata |
| Subphylum: | Tunicata |
| Genus: | †Shankouclava Chen et al., 2003 |
| Type species | |
| †Shankouclava anningense Chen et al., 2003
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| Species | |
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Shankouclava is an extinct genus of tunicates. It is one of two[2][3] candidates for the oldest member of this group, dating to 518 million years ago. 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.[4]
Morphology
[edit]Shankouclava had a soft, sac-like body that was elongated and pointed proximally. The body lengths of individuals vary from 2 cm (0.8 in) to 4 cm (1.6 in).[4]
Etymology
[edit]The generic name is composed of the fossil locality, Shankou, and the Latin word clava (club-shaped).[4]
Classification
[edit]A stem group tunicate affinity for Shankouclava has been broadly accepted,[citation needed] though some authors have expressed reservations that the evidence in favour of this affinity is not conclusive.[5]
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.[6] This challenge relied on characteristics of newly-discovered Phlogites specimens, and was made despite the lack of obvious Phlogites-like tentacles in the Cheungkongella specimen.[4] A response several years later similarly questioned Shankouclava by way of new Shankouclava-like specimens that clearly display tentacles.[7] While Shankouclava has not been equated with Phlogites, the presence of Phlogites-like tentacles would make a tunicate affinity unlikely.[8]
Another Cambrian tunicate, Megasiphon, known from a single specimen from the slightly younger Marjum Formation, resembles more closely the morphology of surviving tunicates.[9]
References
[edit]- ^ Yang, C.; Li, X.-H.; Zhu, M.; Condon, D. J.; Chen, J. (2018). "Geochronological constraint on the Cambrian Chengjiang biota, South China" (PDF). Journal of the Geological Society. 175 (4): 659–666. Bibcode:2018JGSoc.175..659Y. doi:10.1144/jgs2017-103. ISSN 0016-7649. S2CID 135091168.
- ^ Janvier, Philippe (April 23, 2015). "Facts and fancies about early fossil chordates and vertebrates". Nature. 520: 483–89. doi:10.1038/nature14437.
- ^ Northcutt, R. Glenn (June 26, 2012). "Evolution of centralized nervous systems: Two schools of evolutionary thought". Proceedings of the National Academy of Sciences of the United States of America. 109 (Supplement 1: In the Light of Evolution VI: Brain and Behavior): 10626–10633. JSTOR 41601648.
- ^ a b c d Chen, Jun-Yuan; Huang, Di-Ying; Peng, Qing-Qing; Chi, Hui-Mei; Wang, Xiu-Qiang; Feng, Man (2003). "The first tunicate from the Early Cambrian of South China". Proceedings of the National Academy of Sciences. 100 (14): 8314–8318. Bibcode:2003PNAS..100.8314C. doi:10.1073/pnas.1431177100. PMC 166226. PMID 12835415.
- ^ Conway Morris (29 June 2006). "Darwin's dilemma: the realities of the Cambrian 'explosion'". Philos Trans R Soc Lond B Biol Sci. 361 (1470): 1069–1083. doi:10.1098/rstb.2006.1846. PMC 1578734. PMID 16754615.
- ^ Gee, Henry (July 4, 2018). "Tunicates". Across the Bridge: Understanding the Origin of Vertebrates. University of Chicago Press. pp. 85–99. ISBN 978-0226402864.
- ^ Shu (2008). "Cambrian explosion: Birth of tree of animals". Gondwana Research. 14 (1–2): 219–240. Bibcode:2008GondR..14..219S. doi:10.1016/j.gr.2007.08.004.
- ^ Shu, D.-G.; Conway Morris, S.; Zhang, Z.-F.; Han, J. (2010). "The earliest history of the deuterostomes: The importance of the Chengjiang Fossil-Lagerstätte". Proceedings of the Royal Society B: Biological Sciences. 277 (1679): 165–174. doi:10.1098/rspb.2009.0646. PMC 2842668. PMID 19439437.
- ^ Nanglu, Karma; Lerosey-Aubril, Rudy; Weaver, James C.; Ortega-Hernández, Javier (2023). "A mid-Cambrian tunicate and the deep origin of the ascidiacean body plan". Nature Communications. 14 (1): 3832. doi:10.1038/s41467-023-39012-4. PMC 10325964. PMID 37414759.
