Cambrian stem-group ambulacrarians and the nature of the ancestral deuterostome
Li, Yujing Dunn, Frances S Murdock, Duncan JE Guo, Jin Cong, Peiyun
Li, Yujing
Dunn, Frances S
Murdock, Duncan JE
Guo, Jin
Cong, Peiyun
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10/05/2023
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2022-09-20
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Cambrian
Deuterostomia
Ambulacraria
Cambroernida
Chengjiang biota
palaeobiology
evolution
Deuterostomia
Ambulacraria
Cambroernida
Chengjiang biota
palaeobiology
evolution
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Abstract
Deuterostomes are characterized by some of the most widely divergent body plans in the animal kingdom. These striking morphological differences have hindered efforts to predict ancestral characters, with the origin and earliest evolution of the group remaining ambiguous. Several iconic Cambrian fossils have been suggested to be early deuterostomes and hence could help elucidate ancestral character states. However, their phylogenetic relationships are controversial. Here, we describe new, exceptionally preserved specimens of the discoidal metazoan Rotadiscus grandis from the early Cambrian Chengjiang biota of China. These reveal a previously unknown double spiral structure, which we interpret as a chordate-like covering to a coelomopore, located adjacent to a horseshoe-shaped tentacle complex. The tentacles differ in key aspects from those seen in lophophorates and are instead more similar to the tentacular systems of extant pterobranchs and echinoderms. Thus, Rotadiscus exhibits a chimeric combination of ambulacrarian and chordate characters. Phylogenetic analyses recover Rotadiscus and closely related fossil taxa as stem ambulacrarians, filling a significant morphological gap in the deuterostome tree of life. These results allow us to reconstruct the ancestral body plans of major clades of deuterostomes, revealing that key traits of extant forms, such as a post-analregion, gillbars, and a U-shaped gut, evolved through convergence.
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Yujing Li, Frances S. Dunn, Duncan J.E. Murdock, Jin Guo, Imran A. Rahman, Peiyun Cong, Cambrian stem-group ambulacrarians and the nature of the ancestral deuterostome, Current Biology, 2023, , ISSN 0960-9822, https://doi.org/10.1016/j.cub.2023.04.048.
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Copyright © 2023 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
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0960-9822
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openAccess