Fossil Friday: Kinorhyncha, Yet Another Animal Body Plan from the Cambrian Explosion
This Fossil Friday we will look at an obscure group of animals from a clade of molting invertebrate animals called Ecdysozoa that include the roundworm phyla (Nematoda, Nematomorpha, Priapulida, Loricifera, and Kinorhyncha) as well as tardigrades, velvet worms (Onychophora), extinct lobopods, and arthropods (Telford et al. 2009). Almost all of these ecdysozoan phyla have been recorded from the Lower Cambrian and thus clearly originated with the burst of biological creativity in the Cambrian Explosion, which brought forth all the different animal body plans. As usual the molecular clock estimates would suggest an ancient origin of ecdysozoans deep within the Ediacaran period (Howard 2021, Howard et al. 2020, 2022), which is “highlighting major discrepancy with the known fossil record of the group” (Wang et al. 2024).
Indeed, apart from some dubious trace fossils and microfossils from the terminal Ediacaran (Vannier et al. 2010, Buatois et al. 2014, Moczydłowska et al. 2015, Parry et al. 2017, Chen et al. 2018, 2019, Kesidis et al. 2019, Turk et al. 2021), unequivocal body fossils of the ecdysozoan phyla (i.e., Priapulida and Loricifera) are first appearing in the Early to Middle Cambrian. The extinct Palaeoscolecida (Early Cambrian – Silurian) are considered to be either stem nematomorphs (Hou & Bergström 1994) or rather stem priapulids (Whitaker et al. 2020). Maas et al. (2010) described a possible stem Nematoida (Nematoda+Nematomorpha) from the Middle Cambrian of Australia, but its closer affinities remain unknown. A notable gap in our knowledge of ecdysozoan history was the phylum Kinorhyncha, which until recently had no known fossil record at all. These animals are small marine invertebrates that are also called mud dragons because of their spiny body.
Hardly a decade ago, Chinese scientists described “three dimensionally phosphatized worm-like fossils from the early Cambrian rocks, approximately 535 million years old, in northern Sichuan and southern Shaanxi provinces” of South China (Zhang et al. 2015; also see Fang 2015 and NGIP 2016). They were interpreted as early kinorhynchs and therefore named Eokinorhynchus rarus (featured above). The 2 mm long animals only differed from their living relatives in having more body segments and more distinct spines. In other words: the earliest kinorhynchs were more complex than modern ones. So much for the evolutionary narrative from simple to complex.
Defying Darwinian Explanations
Five years later, Shao et al. (2020) described Zhongpingscolex qinensis from the Early Cambrian (Fortunian Stage) of South China. Their phylogenetic analysis resolved this new taxon as closest relative (sister group) of Eokinorhynchus in the stem group of Kinorhyncha.The authors did not mention three undescribed taxa of fossil kinorynchs with up to 40 mm length from the Middle Cambrian Qingjiang biota in China (Fu et al. 2019; also see Daley 2019).
Based on these findings we can safely count Kinorhyncha among the large number of animal phyla that originated abruptly in the Cambrian Explosion. The more we learn about the fossil record the more the Cambrian Explosion is confirmed as a key event in the history of life, which defies Darwinian explanations
References
Buatois LA, Narbonne GM, Mangano MG, Carmona NB & Myrow P 2014. Ediacaran matground ecology persisted into the earliest Cambrian. Nature Communications 5: 3544, 1–5. DOI: https://doi.org/10.1038/ncomms4544
Chen Z, Chen X, Zhou C, Yuan X & Xiao S 2018. Late Ediacaran trackways produced by bilaterian animals with paired appendages. Science Advances 4(6): eaao6691, 1–8. DOI: https://doi.org/10.1126/sciadv.aao6691
Chen Z, Zhou C, Yuan XL & Xiao SH 2019. Death march of a segmented and trilobate bilaterian elucidates early animal evolution. Nature 573, 412–415. DOI: https://doi.org/10.1038/s41586-019-1522-7
Daley AC 2019. A treasure trove of Cambrian fossils. Science 363(6433), 1284–1285. DOI: https://doi.org/10.1126/science.aaw8644
Fang J 2015. Spiky, Armored Worm Lived Half A Billion Years Ago. IFL Science November 26, 2015. https://www.iflscience.com/spiky-armored-worm-lived-half-billion-years-ago-32315
Fu D, Tong G, Dai T, Liu W, Yang Y, Zhang Y, Cui L, Li L, Yun H, Wu Y, Sun A, Liu C, Pei W, Gaines RR & Zhang X 2019. The Qingjiang biota—A Burgess Shale–type fossil Lagerstätte from the early Cambrian of South China. Science 363(6433), 1338–1342. DOI: https://doi.org/10.1126/science.aau8800
Howard R 2021. The Deep Evolution of Ecdysozoa. Ph.D. thesis, University of Exeter, 459 pp. https://www.proquest.com/openview/257f91384a25d9c55ea9980ed27b561f/&diss=y
Howard RJ, Edgecombe GD, Shi X, Hou X & Ma X 2020. Ancestral morphology of Ecdysozoa constrained by an early Cambrian stem group ecdysozoan. BMC Evolutionary Biology 20(1): 156, 1–18. DOI: https://doi.org/10.1186/s12862-020-01720-6
Howard RJ, Giacomelli M, Lozano-Fernandez J, Edgecombe GD, Fleming JF, Kristensen RM, Ma X, Olesen J, Sørensen MV, Thomsen PF, Wills MA, Donoghue PCJ & Pisani D 2022. The Ediacaran origin of Ecdysozoa: integrating fossil and phylogenomic data. Journal of the Geological Society 179, 1–14. DOI: https://doi.org/10.1144/jgs2021-107
Hou X & Bergström J 1994. Palaeoscolecid worms may be nematomorphs rather than annelids. Lethaia 27(1), 11–17. DOI: https://doi.org/10.1111/j.1502-3931.1994.tb01548.x
Kesidis G, Slater BJ, Jensen S & Budd GE 2019. Caught in the act: priapulid burrowers in early Cambrian substrates. Proceedings of the Royal Society B 286(1894), 20182505, 1–8. DOI: https://doi.org/10.1098/rspb.2018.2505
Maas A, Waloszek D, Haug J & Müller K 2007. A possible larval roundworm from the Cambrian ‘Orsten’ and its bearing on the phylogeny of Cycloneuralia. Memoirs of the Association of Australasian Palaeontologists 34, 499–519. https://www.researchgate.net/publication/238695144
Moczydłowska M, Budd GE & Agić H 2015. Ecdysozoan-like sclerites among Ediacaran microfossils. Geological Magazine 152(06), 1145–1148. DOI: https://doi.org/10.1017/S001675681500045X
NIGP 2016. Scientists Found the First Fossil Record of Kinorhyncha (Scientific Reports, 2015). Nanjing Institute of Geology and Palaeontology Palaeonews No. 2 2015. http://english.nigpas.cas.cn/ns/palaeonews/no2/201602/t20160205_159614.html
Parry LA, Boggiani PC, Condon DJ, Garwood RJ, Leme JDM, McIlroy D, Brasier MD, Trindade R, Campanha GAC, Pacheco MLAF, Diniz CQC & Liu AG 2017. Ichnological evidence for meiofaunal bilaterians from the terminal Ediacaran and earliest Cambrian of Brazil. Nature Ecology & Evolution 1, 1455–1464. DOI: https://doi.org/10.1038/s41559-017-0301-9
Shao TQ, Wang Q, Liu YH, Qin JC, Zhang YN, Liu MJ, Shao Y, Zhao JY & Zhang HQ 2020. A new scalidophoran animal from the Cambrian Fortunian Stage of South China and its implications for the origin and early evolution of Kinorhyncha. Precambrian Research 349: 105616, 1–9. DOI: https://doi.org/10.1016/j.precamres.2020.105616
Telford MJ, Bourlat SJ, Economou A, Papillon D & Rota-Stabelli O 2009. The origins and evolution of the Ecdysozoa. Chapter 8, pp. 71–79 in: Telford MJ & Littlewood DTJ (eds). Animal Evolution: Genomes, Fossils, and Trees. Oxford University Press, Oxford (UK), xvi+245 pp. DOI: https://doi.org/10.1093/acprof:oso/9780199549429.003.0008
Turk KA, Maloney KM, Laflamme M & Darroch SAF 2021. Priapulid Trace Fossils from the Late Ediacaran of Namibia. Conference GSA Connects 2021, Portland (OR). https://gsa.confex.com/gsa/2021AM/webprogram/Paper369978.html
Vannier J, Calandra I, Gaillard C & Żylińska A 2010. Priapulid worms: Pioneer horizontal burrowers at the Precambrian-Cambrian boundary. Geology 38(8), 711–714. DOI: https://doi.org/10.1130/G30829.1
Wang D, Qiang Y, Guo J, Vannier J, Song Z, Peng J, Zhang B, Sun J, Yu Y, Zhang Y, Zhang T, Yang X & Han J 2024. Early evolution of the ecdysozoan body plan. eLife Preprint, 1–22. DOI: https://doi.org/10.7554/eLife.94709.1
Whitaker AF, Jamison PG, Schiffbauer JD & Kimmig J 2020. Re-description of the Spence Shale palaeoscolecids in light of new morphological features with comments on palaeoscolecid taxonomy and taphonomy. PalZ 94(4), 661–674. DOI: https://doi.org/10.1007/s12542-020-00516-9
Zhang H, Xiao S, Liu Y, Yuan X, Wan B, Muscente AD, Shao T, Gong H & Cao, G. 2015. Armored kinorhynch-like scalidophoran animals from the early Cambrian. Scientific Reports 5(1): 16521, 1–10. DOI: https://doi.org/10.1038/srep16521
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