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.

History of identification

C. tylodes was initially tentatively classified as a stem group echinoderm in 1996, and then a lophophorate in 2002. 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.

A more recent alternative proposal suggested a relationship with the Cambroernida, a group of early deuterostomes. However, a later comprehensive paper on cambroernids did not include Cotyledion.

A comprehensive 2013 study of around 400 new specimens provided stronger support for a lophophorate affinity, specifically allied with the entoprocts. 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. A recent review of echinoderm origins again refuted the placement of Cotyledion with that group, agreeing with its identity as a stem entoproct.

See also

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:. doi:.
  • 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:.
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  • Yang, Xianfeng; Kimmig, Julie; Lieberman, Bruce S.; Peng, Shanchi (2020). . The Science of Nature. 107 (37). doi:. PMC .
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