The Cambrian cirratuliform Iotuba denotes an early annelid radiation

Zhang, Z.-F.; Smith, M.R.; Ren, X.-Y

Abstract

The principal animal lineages (phyla) diverged in the Cambrian, but most diversity at lower taxonomic ranks arose more gradually over the subsequent 500 Myr. Annelid worms seem to exemplify this pattern, based on molecular analyses and the fossil record: Cambrian Burgess Shale-type deposits host a single, early-diverging crown-group annelid alongside a morphologically and taxonomically conservative stem group; the polychaete sub-classes diverge in the Ordovician; and many orders and families are first documented in Carboniferous Lagerstätten. Fifteen new fossils of the ‘phoronid’ Iotuba (=Eophoronis) chengjiangensis from the early Cambrian Chengjiang Lagerstätte challenge this picture. A chaetal cephalic cage surrounds a retractile head with branchial plates, affiliating Iotuba with the derived polychaete families ‘Flabelligeridae’ and Acrocirridae. Unless this similarity represents profound convergent evolution, this relationship would pull back the origin of the nested crown groups of Cirratuliformia, Sedentaria and Pleistoannelida by tens of millions of years—indicating a dramatic unseen origin of modern annelid diversity in the heat of the Cambrian ‘explosion’.

Citation

Zhang, Z.-F., Smith, M., & Ren, X.-Y. (2023). The Cambrian cirratuliform Iotuba denotes an early annelid radiation. Proceedings of the Royal Society B: Biological Sciences, 290(1992), Article 20222014. https://doi.org/10.1098/rspb.2022.2014

• Journal Article Type: Article
• Acceptance Date: Jan 9, 2023
• Online Publication Date: Feb 1, 2023
• Publication Date: 2023
• Deposit Date: Jan 10, 2023
• Publicly Available Date: May 31, 2023
• Journal: Proceedings of the Royal Society B: Biological Sciences
• Print ISSN: 0962-8452
• Electronic ISSN: 1471-2954
• Publisher: The Royal Society
• Peer Reviewed: Peer Reviewed
• Volume: 290
• Issue: 1992
• Article Number: 20222014
• DOI: https://doi.org/10.1098/rspb.2022.2014
• Public URL: https://durham-repository.worktribe.com/output/1183769
• Publisher URL: https://royalsocietypublishing.org/journal/rspb