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Ancestral morphology of Ecdysozoa constrained by an early Cambrian stem group ecdysozoan

BACKGROUND: Ecdysozoa are the moulting protostomes, including arthropods, tardigrades, and nematodes. Both the molecular and fossil records indicate that Ecdysozoa is an ancient group originating in the terminal Proterozoic, and exceptional fossil biotas show their dominance and diversity at the beg...

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Autores principales: Howard, Richard J., Edgecombe, Gregory D., Shi, Xiaomei, Hou, Xianguang, Ma, Xiaoya
Formato: Online Artículo Texto
Lenguaje:English
Publicado: BioMed Central 2020
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7684930/
https://www.ncbi.nlm.nih.gov/pubmed/33228518
http://dx.doi.org/10.1186/s12862-020-01720-6
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author Howard, Richard J.
Edgecombe, Gregory D.
Shi, Xiaomei
Hou, Xianguang
Ma, Xiaoya
author_facet Howard, Richard J.
Edgecombe, Gregory D.
Shi, Xiaomei
Hou, Xianguang
Ma, Xiaoya
author_sort Howard, Richard J.
collection PubMed
description BACKGROUND: Ecdysozoa are the moulting protostomes, including arthropods, tardigrades, and nematodes. Both the molecular and fossil records indicate that Ecdysozoa is an ancient group originating in the terminal Proterozoic, and exceptional fossil biotas show their dominance and diversity at the beginning of the Phanerozoic. However, the nature of the ecdysozoan common ancestor has been difficult to ascertain due to the extreme morphological diversity of extant Ecdysozoa, and the lack of early diverging taxa in ancient fossil biotas. RESULTS: Here we re-describe Acosmia maotiania from the early Cambrian Chengjiang Biota of Yunnan Province, China and assign it to stem group Ecdysozoa. Acosmia features a two-part body, with an anterior proboscis bearing a terminal mouth and muscular pharynx, and a posterior annulated trunk with a through gut. Morphological phylogenetic analyses of the protostomes using parsimony, maximum likelihood and Bayesian inference, with coding informed by published experimental decay studies, each placed Acosmia as sister taxon to Cycloneuralia + Panarthropoda—i.e. stem group Ecdysozoa. Ancestral state probabilities were calculated for key ecdysozoan nodes, in order to test characters inferred from fossils to be ancestral for Ecdysozoa. Results support an ancestor of crown group ecdysozoans sharing an annulated vermiform body with a terminal mouth like Acosmia, but also possessing the pharyngeal armature and circumoral structures characteristic of Cambrian cycloneuralians and lobopodians. CONCLUSIONS: Acosmia is the first taxon placed in the ecdysozoan stem group and provides a constraint to test hypotheses on the early evolution of Ecdysozoa. Our study suggests acquisition of pharyngeal armature, and therefore a change in feeding strategy (e.g. predation), may have characterised the origin and radiation of crown group ecdysozoans from Acosmia-like ancestors.
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spelling pubmed-76849302020-11-25 Ancestral morphology of Ecdysozoa constrained by an early Cambrian stem group ecdysozoan Howard, Richard J. Edgecombe, Gregory D. Shi, Xiaomei Hou, Xianguang Ma, Xiaoya BMC Evol Biol Research Article BACKGROUND: Ecdysozoa are the moulting protostomes, including arthropods, tardigrades, and nematodes. Both the molecular and fossil records indicate that Ecdysozoa is an ancient group originating in the terminal Proterozoic, and exceptional fossil biotas show their dominance and diversity at the beginning of the Phanerozoic. However, the nature of the ecdysozoan common ancestor has been difficult to ascertain due to the extreme morphological diversity of extant Ecdysozoa, and the lack of early diverging taxa in ancient fossil biotas. RESULTS: Here we re-describe Acosmia maotiania from the early Cambrian Chengjiang Biota of Yunnan Province, China and assign it to stem group Ecdysozoa. Acosmia features a two-part body, with an anterior proboscis bearing a terminal mouth and muscular pharynx, and a posterior annulated trunk with a through gut. Morphological phylogenetic analyses of the protostomes using parsimony, maximum likelihood and Bayesian inference, with coding informed by published experimental decay studies, each placed Acosmia as sister taxon to Cycloneuralia + Panarthropoda—i.e. stem group Ecdysozoa. Ancestral state probabilities were calculated for key ecdysozoan nodes, in order to test characters inferred from fossils to be ancestral for Ecdysozoa. Results support an ancestor of crown group ecdysozoans sharing an annulated vermiform body with a terminal mouth like Acosmia, but also possessing the pharyngeal armature and circumoral structures characteristic of Cambrian cycloneuralians and lobopodians. CONCLUSIONS: Acosmia is the first taxon placed in the ecdysozoan stem group and provides a constraint to test hypotheses on the early evolution of Ecdysozoa. Our study suggests acquisition of pharyngeal armature, and therefore a change in feeding strategy (e.g. predation), may have characterised the origin and radiation of crown group ecdysozoans from Acosmia-like ancestors. BioMed Central 2020-11-23 /pmc/articles/PMC7684930/ /pubmed/33228518 http://dx.doi.org/10.1186/s12862-020-01720-6 Text en © The Author(s) 2020 Open AccessThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.
spellingShingle Research Article
Howard, Richard J.
Edgecombe, Gregory D.
Shi, Xiaomei
Hou, Xianguang
Ma, Xiaoya
Ancestral morphology of Ecdysozoa constrained by an early Cambrian stem group ecdysozoan
title Ancestral morphology of Ecdysozoa constrained by an early Cambrian stem group ecdysozoan
title_full Ancestral morphology of Ecdysozoa constrained by an early Cambrian stem group ecdysozoan
title_fullStr Ancestral morphology of Ecdysozoa constrained by an early Cambrian stem group ecdysozoan
title_full_unstemmed Ancestral morphology of Ecdysozoa constrained by an early Cambrian stem group ecdysozoan
title_short Ancestral morphology of Ecdysozoa constrained by an early Cambrian stem group ecdysozoan
title_sort ancestral morphology of ecdysozoa constrained by an early cambrian stem group ecdysozoan
topic Research Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7684930/
https://www.ncbi.nlm.nih.gov/pubmed/33228518
http://dx.doi.org/10.1186/s12862-020-01720-6
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