Heterochrony and parallel evolution of echinoderm, hemichordate and cephalochordate internal bars
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Issue date
2022-05-11Submitted date
2022-02-09Subject Terms
deuterostomesStylophora
pharyngeal openings
gill bars
homology
respiratory structures
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Show full item recordAbstract
Deuterostomes comprise three phyla with radically different body plans. Phylogenetic bracketing of the living deuterostome clades suggests the latest common ancestor of echinoderms, hemichordates and chordates was a bilaterally symmetrical worm with pharyngeal openings, with these characters lost in echinoderms. Early fossil echinoderms with pharyngeal openings have been described, but their interpretation is highly controversial. Here, we critically evaluate the evidence for pharyngeal structures (gill bars) in the extinct stylophoran echinoderms Lagynocystis pyramidalis and Jaekelocarpus oklahomensis using virtual models based on high-resolution X-ray tomography scans of three-dimensionally preserved fossil specimens. Multivariate analyses of the size, spacing and arrangement of the internal bars in these fossils indicate they are substantially more similar to gill bars in modern enteropneust hemichordates and cephalochordates than to other internal bar-like structures in fossil blastozoan echinoderms. The close similarity between the internal bars of the stylophorans L. pyramidalis and J. oklahomensis and the gill bars of extant chordates and hemichordates is strong evidence for their homology. Differences between these internal bars and bar-like elements of the respiratory systems in blastozoans suggest these structures might have arisen through parallel evolution across deuterostomes, perhaps underpinned by a common developmental genetic mechanism.Citation
Álvarez-Armada Nidia, Cameron Christopher B., Bauer Jennifer E. and Rahman Imran A. 2022Heterochrony and parallel evolution of echinoderm, hemichordate and cephalochordate internal bars Proc. R. Soc. B.2892022025820220258 http://doi.org/10.1098/rspb.2022.0258Publisher
The Royal SocietyType
Journal ArticleItem Description
© 2022 The Authors. Published by the Royal Society under the terms of the Creative Commons AttributionLicense http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the originalauthor and source are credited.ISSN
0962-8452EISSN
1471-2954ae974a485f413a2113503eed53cd6c53
10.1098/rspb.2022.0258
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