A new Cambrian stem-group echinoderm reveals the evolution of the anteroposterior axis
Woodgate, Stephanie C Dunn, Frances S Thompson, Jeffrey R Formery, Laurent Zamora, Samuel
Woodgate, Stephanie C
Dunn, Frances S
Thompson, Jeffrey R
Formery, Laurent
Zamora, Samuel
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2025-06-25
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2025-02-20
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Cambrian
echinoderms
ctenocystoids
paleobiology
phylogeny
evolution
anteroposterior axis
echinoderms
ctenocystoids
paleobiology
phylogeny
evolution
anteroposterior axis
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Abstract
Echinoderms are among the most morphologically distinctive animal phyla, encompassing familiar forms like starfish and sea urchins. Uncovering how their unique pentaradial body plan evolved from a bilaterally symmetrical ancestor has long proved challenging, as this involved fundamental changes to adult morphology and body plan development, associated with a complete reorganization of the anteroposterior (A-P) axis,1–3 obfuscating homologies between disparate groups.4,5 This has greatly limited our understanding of one of the most radical transformations in bilaterian evolutionary history.6–8 Here, we describe a new bilaterally symmetrical echinoderm, Atlascystis acantha, from the Cambrian of Morocco.9 This is the oldest bilaterally symmetrical echinoderm and the first with this body plan known from different ontogenetic stages, allowing us to elucidate mechanisms ofits growth. Thisdemonstrates thatAtlascystis possessed ambulacra—structures accommodating extensions of the characteristic echinoderm water vascular system—providing a clear point of homology betweenAtlascystis andradially symmetricalforms. By integrating the Cambrian fossilrecordandour newphylogeny with developmental biology,10 we uncover how changes to the ancestral bilaterian A-P patterning network alongside stepwise morphological transformations gave rise to the pentaradial structure of extant echinoderms, transforming our understanding of the origin and earliest evolution of this major animal phylum.
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Woodgate et al., A new Cambrian stem-group echinoderm reveals the evolution of the anteroposterior axis, Current Biology (2025), https://doi.org/10.1016/j.cub.2025.05.065
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Copyright © 2025 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/). The linked file is the publshed version of the article.
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0960-9822
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openAccess