Cotyledion tylodes is an extinct, stalked filter-feeder known from the Chengjiang lagerstatten. The living animal reached a couple of centimetres in height, and bore a loose scleritome of ovoid sclerites. Its interpretation has been controversial, but it is currently thought to be a member of the Entoprocta stem group.[2]
History of identification
C. tylodes was initially tentatively classified as a stem group echinoderm in 1996, and then a lophophorate in 2002.[2] Lophphorate affinities were challenged as based on taphonomic artifacts in a 2010 paper that suggested a cnidarian affinity based on cylyndrical symmetry as an ancestral body plan for that group.[3]
A more recent alternative proposal suggested a relationship with the Cambroernida, a group of early deuterostomes.[4] However, a later comprehensive paper on cambroernids did not include Cotyledion.[5]
A comprehensive 2013 study of around 400 new specimens provided stronger support for a lophophorate affinity, specifically allied with the entoprocts.[2] The clear presence of a U-shaped gut in the new specimens contradicts placement among the cnidarians, while the lack of bifurcation in the crown of tentacles makes affinity with the deuterostomes unlikely.[6] A recent review of echinoderm origins again refuted the placement of Cotyledion with that group, agreeing with its identity as a stem entoproct.[7]
See also
References
- ^ Zhang et al. 2013
- ^ a b c d Hou et al. 2017
- ^ Clausen et al. 2010, p. 137
- ^ Yang et al. 2020
- ^ Li et al. 2023
- ^ Zhang et al. 2013, pp. 3–5
- ^ Rahman & Zamora 2024, p. 301
Works cited
- Clausen, S. B.; Hou, X. G.; Bergström, J.; Franzén, C. (2010). "The absence of echinoderms from the Lower Cambrian Chengjiang fauna of China: Palaeoecological and palaeogeographical implications". Palaeogeography, Palaeoclimatology, Palaeoecology. 294 (3–4): 133–141. Bibcode:2010PPP...294..133C. doi:10.1016/j.palaeo.2010.01.001.
- Hou, Xian-guang; Siveter, David J.; Siveter, Derek J.; Aldridge, Richard J.; Cong, Pei-yun; Gabbott, Sarah; Ma, Xiao-ya; Purnell, Mark A.; Williams, Mark (2017). "Entoprocta". The Cambrian Fossils of Chengjiang, China: The Flowering of Early Animal Life (2 ed.). pp. 82–83. doi:10.1002/9781118896372.ch25.
- Li, Yujing; Dunn, Frances S.; Murdock, Duncan J.E.; Guo, Jin; Rahman, Imran A.; Cong, Peiyun (May 10, 2023). "Cambrian stem-group ambulacrarians and the nature of the ancestral deuterostome". Current Biology. doi:10.1016/j.cub.2023.04.048. PMID 37167976. S2CID 258592223. Retrieved 11 May 2023.
- Rahman, Imran A.; Zamora, Samuel (July 2024). "Origin and early evolution of echinoderms". Annual Review of Earth and Planetary Sciences. 52: 295–320. doi:10.1146/annurev-earth-031621-113343. hdl:10141/623070.
- Yang, Xianfeng; Kimmig, Julie; Lieberman, Bruce S.; Peng, Shanchi (2020). "A new species of the deuterostome Herpetogaster from the early Cambrian Chengjiang biota of South China". The Science of Nature. 107 (37). doi:10.1007/s00114-020-01695-w. PMC 7544619.
- Zhang, Z.; Holmer, L. E.; Skovsted, C. B.; Brock, G. A.; Budd, G. E.; Fu, D.; Zhang, X.; Shu, D.; Han, J.; Liu, J.; Wang, H.; Butler, A. N.; Li, G. (2013). "A sclerite-bearing stem group entoproct from the early Cambrian and its implications". Scientific Reports. 3: 1066. Bibcode:2013NatSR...3E1066Z. doi:10.1038/srep01066. PMC 3548229. PMID 23336066.
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